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Walker LM, Sherpa RN, Ivaturi S, Brock DA, Larsen TJ, Walker JR, Strassmann JE, Queller DC. Parallel evolution of the G protein-coupled receptor GrlG and the loss of fruiting body formation in the social amoeba Dictyostelium discoideum evolved under low relatedness. G3 (BETHESDA, MD.) 2023; 14:jkad235. [PMID: 37832511 PMCID: PMC10755179 DOI: 10.1093/g3journal/jkad235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 07/25/2023] [Accepted: 09/27/2023] [Indexed: 10/15/2023]
Abstract
Aggregative multicellularity relies on cooperation among formerly independent cells to form a multicellular body. Previous work with Dictyostelium discoideum showed that experimental evolution under low relatedness profoundly decreased cooperation, as indicated by the loss of fruiting body formation in many clones and an increase of cheaters that contribute proportionally more to spores than to the dead stalk. Using whole-genome sequencing and variant analysis of these lines, we identified 38 single nucleotide polymorphisms in 29 genes. Each gene had 1 variant except for grlG (encoding a G protein-coupled receptor), which had 10 unique SNPs and 5 structural variants. Variants in the 5' half of grlG-the region encoding the signal peptide and the extracellular binding domain-were significantly associated with the loss of fruiting body formation; the association was not significant in the 3' half of the gene. These results suggest that the loss of grlG was adaptive under low relatedness and that at least the 5' half of the gene is important for cooperation and multicellular development. This is surprising given some previous evidence that grlG encodes a folate receptor involved in predation, which occurs only during the single-celled stage. However, non-fruiting mutants showed little increase in a parallel evolution experiment where the multicellular stage was prevented from happening. This shows that non-fruiting mutants are not generally selected by any predation advantage but rather by something-likely cheating-during the multicellular stage.
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Affiliation(s)
- Laura M Walker
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Rintsen N Sherpa
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI 48109, USA
| | - Sindhuri Ivaturi
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Debra A Brock
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Tyler J Larsen
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Jason R Walker
- McDonnell Genome Institute, Washington University School of Medicine, St. Louis, MO 63130, USA
| | - Joan E Strassmann
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - David C Queller
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
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2
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Larsen TJ, Jahan I, Brock DA, Strassmann JE, Queller DC. Reduced social function in experimentally evolved Dictyostelium discoideum implies selection for social conflict in nature. Proc Biol Sci 2023; 290:20231722. [PMID: 38113942 PMCID: PMC10730294 DOI: 10.1098/rspb.2023.1722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 11/21/2023] [Indexed: 12/21/2023] Open
Abstract
Many microbes interact with one another, but the difficulty of directly observing these interactions in nature makes interpreting their adaptive value complicated. The social amoeba Dictyostelium discoideum forms aggregates wherein some cells are sacrificed for the benefit of others. Within chimaeric aggregates containing multiple unrelated lineages, cheaters can gain an advantage by undercontributing, but the extent to which wild D. discoideum has adapted to cheat is not fully clear. In this study, we experimentally evolved D. discoideum in an environment where there were no selective pressures to cheat or resist cheating in chimaeras. Dictyostelium discoideum lines grown in this environment evolved reduced competitiveness within chimaeric aggregates and reduced ability to migrate during the slug stage. By contrast, we did not observe a reduction in cell number, a trait for which selection was not relaxed. The observed loss of traits that our laboratory conditions had made irrelevant suggests that these traits were adaptations driven and maintained by selective pressures D. discoideum faces in its natural environment. Our results suggest that D. discoideum faces social conflict in nature, and illustrate a general approach that could be applied to searching for social or non-social adaptations in other microbes.
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Affiliation(s)
- Tyler J. Larsen
- Department of Biology, Washington University in St. Louis, St. Louis, MO, USA
| | - Israt Jahan
- Department of Biology, Washington University in St. Louis, St. Louis, MO, USA
| | - Debra A. Brock
- Department of Biology, Washington University in St. Louis, St. Louis, MO, USA
| | - Joan E. Strassmann
- Department of Biology, Washington University in St. Louis, St. Louis, MO, USA
| | - David C. Queller
- Department of Biology, Washington University in St. Louis, St. Louis, MO, USA
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3
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Forget M, Adiba S, Brunnet LG, De Monte S. Heterogeneous individual motility biases group composition in a model of aggregating cells. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.1052309] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Aggregative life cycles are characterized by alternating phases of unicellular growth and multicellular development. Their multiple, independent evolutionary emergence suggests that they may have coopted pervasive properties of single-celled ancestors. Primitive multicellular aggregates, where coordination mechanisms were less efficient than in extant aggregative microbes, must have faced high levels of conflict between different co-aggregating populations. Such conflicts within a multicellular body manifest in the differential reproductive output of cells of different types. Here, we study how heterogeneity in cell motility affects the aggregation process and creates a mismatch between the composition of the population and that of self-organized groups of active adhesive particles. We model cells as self-propelled particles and describe aggregation in a plane starting from a dispersed configuration. Inspired by the life cycle of aggregative model organisms such as Dictyostelium discoideum or Myxococcus xanthus, whose cells interact for a fixed duration before the onset of chimeric multicellular development, we study finite-time configurations for identical particles and in binary mixes. We show that co-aggregation results in three different types of frequency-dependent biases, one of which is associated to evolutionarily stable coexistence of particles with different motility. We propose a heuristic explanation of such observations, based on the competition between delayed aggregation of slower particles and detachment of faster particles. Unexpectedly, despite the complexity and non-linearity of the system, biases can be largely predicted from the behavior of the two corresponding homogenous populations. This model points to differential motility as a possibly important factor in driving the evolutionary emergence of facultatively multicellular life-cycles.
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4
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Adiba S, Forget M, De Monte S. Evolving social behaviour through selection of single-cell adhesion in Dictyostelium discoideum. iScience 2022; 25:105006. [PMID: 36105585 PMCID: PMC9464967 DOI: 10.1016/j.isci.2022.105006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 06/09/2022] [Accepted: 08/19/2022] [Indexed: 11/30/2022] Open
Abstract
The social amoeba Dictyostelium discoideum commonly forms chimeric fruiting bodies. Genetic variants that produce a higher proportion of spores are predicted to undercut multicellular organization unless cooperators assort positively. Cell adhesion is considered a primary factor driving such assortment, but evolution of adhesion has not been experimentally connected to changes in social performance. We modified by experimental evolution the efficiency of individual cells in attaching to a surface. Surprisingly, evolution appears to have produced social cooperators irrespective of whether stronger or weaker adhesion was selected. Quantification of reproductive success, cell-cell adhesion, and developmental patterns, however, revealed two distinct social behaviors, as captured when the classical metric for social success is generalized by considering clonal spore production. Our work shows that cell mechanical interactions can constrain the evolution of development and sociality in chimeras and that elucidation of proximate mechanisms is necessary to understand the ultimate emergence of multicellular organization. Cooperative behavior evolved as a pleiotropic effect of selection for surface adhesion Multicellular development of evolved lines with the ancestor follows two different paths A metric of social behavior including clonal development differentiates these two paths
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Affiliation(s)
- Sandrine Adiba
- Institut de Biologie de l’ENS (IBENS), Département de biologie, Ecole normale supérieure, CNRS, INSERM, Université PSL, 75005 Paris, France
- Corresponding author
| | - Mathieu Forget
- Institut de Biologie de l’ENS (IBENS), Département de biologie, Ecole normale supérieure, CNRS, INSERM, Université PSL, 75005 Paris, France
- Department of Evolutionary Theory, Max Planck Institute for Evolutionary Biology, Plön, Germany
| | - Silvia De Monte
- Institut de Biologie de l’ENS (IBENS), Département de biologie, Ecole normale supérieure, CNRS, INSERM, Université PSL, 75005 Paris, France
- Department of Evolutionary Theory, Max Planck Institute for Evolutionary Biology, Plön, Germany
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5
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Abstract
Cooperation has been essential to the evolution of biological complexity, but many societies struggle to overcome internal conflicts and divisions. Dictyostelium discoideum, or the social amoeba, has been a useful model system for exploring these conflicts and how they can be resolved. When starved, these cells communicate, gather into groups, and build themselves into a multicellular fruiting body. Some cells altruistically die to form the rigid stalk, while the remainder sit atop the stalk, become spores, and disperse. Evolutionary theory predicts that conflict will arise over which cells die to form the stalk and which cells become spores and survive. The power of the social amoeba lies in the ability to explore how cooperation and conflict work across multiple levels, ranging from proximate mechanisms (how does it work?) to ultimate evolutionary answers (why does it work?). Recent studies point to solutions to the problem of ensuring fairness, such as the ability to suppress selfishness and to recognize and avoid unrelated individuals. This work confirms a central role for kin selection, but also suggests new explanations for how social amoebae might enforce cooperation. New approaches based on genomics are also enabling researchers to decipher for the first time the evolutionary history of cooperation and conflict and to determine its role in shaping the biology of multicellular organisms.
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Affiliation(s)
- Elizabeth A Ostrowski
- School of Natural and Computational Sciences, Massey University, Auckland, New Zealand.
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6
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Nanjundiah V. Many roads lead to Rome: Neutral phenotypes in microorganisms. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2019; 332:339-348. [PMID: 31617664 DOI: 10.1002/jez.b.22909] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 09/10/2019] [Accepted: 09/14/2019] [Indexed: 11/09/2022]
Abstract
John Bonner pointed out that microorganisms differ in several ways, some of which may reflect neutral phenotypic evolution. For making his case, Bonner referred to interspecies differences and morphological traits. Here we consider intraspecies differences and physiological traits. As a case-study, we examine the production of an extracellular cyclic 3 ' ,5 ' monophosphate phosphodiesterase in the cellular slime mold Dictyostelium discoideum. Temporal profiles of phosphodiesterase activity differ significantly between wild-type strains. From that we argue that the inference drawn initially from studies on a single wild-type, namely that the profile displayed by it pointed to an adaptive role, was mistaken. We generalize the conclusion to suggest that physiological differences exhibited by microorganisms of the same species may, but need not, reflect adaptations to different environments. Rather, the differences could be related to the fact that microorganisms live in groups whose composition can vary between homogeneous (clonal) and heterogeneous (polyclonal). More than one physiological profile is consistent with the normal development of the group in a given environment; the alternatives are neutral. When studying microbial physiology and behavior, it is expected that the observations are made on a clonal population; genetic (and so phenotypic) heterogeneity is carefully guarded against. As the example from D. discoideum shows, an unintended consequence of overlooking phenotypic heterogeneity is that one can fall into the trap of accepting a seemingly plausible, but possibly erroneous, adaptive explanation for a "normal" wild-type phenotype.
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Affiliation(s)
- Vidyanand Nanjundiah
- Centre for Human Genetics, BioTech Park, Bangalore, India.,Stellenbosch Institute for Advanced Study (STIAS), Wallenberg Research Centre at Stellenbosch University, Stellenbosch, South Africa
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7
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Strauss ED, Holekamp KE. Inferring longitudinal hierarchies: Framework and methods for studying the dynamics of dominance. J Anim Ecol 2019; 88:521-536. [PMID: 30664242 DOI: 10.1111/1365-2656.12951] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 01/09/2019] [Indexed: 12/31/2022]
Abstract
Social inequality is a consistent feature of animal societies, often manifesting as dominance hierarchies, in which each individual is characterized by a dominance rank denoting its place in the network of competitive relationships among group members. Most studies treat dominance hierarchies as static entities despite their true longitudinal, and sometimes highly dynamic, nature. To guide study of the dynamics of dominance, we propose the concept of a longitudinal hierarchy: the characterization of a single, latent hierarchy and its dynamics over time. Longitudinal hierarchies describe the hierarchy position (r) and dynamics (∆) associated with each individual as a property of its interaction data, the periods into which these data are divided based on a period delineation rule (p) and the method chosen to infer the hierarchy. Hierarchy dynamics result from both active (∆a) and passive (∆p) processes. Methods that infer longitudinal hierarchies should optimize accuracy of rank dynamics as well as of the rank orders themselves, but no studies have yet evaluated the accuracy with which different methods infer hierarchy dynamics. We modify three popular ranking approaches to make them better suited for inferring longitudinal hierarchies. Our three "informed" methods assign ranks that are informed by data from the prior period rather than calculating ranks de novo in each observation period and use prior knowledge of dominance correlates to inform placement of new individuals in the hierarchy. These methods are provided in an R package. Using both a simulated dataset and a long-term empirical dataset from a species with two distinct sex-based dominance structures, we compare the performance of these methods and their unmodified counterparts. We show that choice of method has dramatic impacts on inference of hierarchy dynamics via differences in estimates of ∆a. Methods that calculate ranks de novo in each period overestimate hierarchy dynamics, but incorporation of prior information leads to more accurately inferred ∆a. Of the modified methods, Informed MatReorder infers the most conservative estimates of hierarchy dynamics and Informed Elo infers the most dynamic hierarchies. This work provides crucially needed conceptual framing and methodological validation for studying social dominance and its dynamics.
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Affiliation(s)
- Eli D Strauss
- Department of Integrative Biology, Michigan State University, East Lansing, Michigan.,Program in Ecology, Evolutionary Biology, and Behavior, Michigan State University, East Lansing, Michigan.,BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan
| | - Kay E Holekamp
- Department of Integrative Biology, Michigan State University, East Lansing, Michigan.,Program in Ecology, Evolutionary Biology, and Behavior, Michigan State University, East Lansing, Michigan.,BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan
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8
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9
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Eldakar OT, Kammeyer JO, Nagabandi N, Gallup AC. Hypocrisy and Corruption: How Disparities in Power Shape the Evolution of Social Control. EVOLUTIONARY PSYCHOLOGY 2018; 16:1474704918756993. [PMID: 29911426 PMCID: PMC10481073 DOI: 10.1177/1474704918756993] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Accepted: 01/07/2018] [Indexed: 11/17/2022] Open
Abstract
Altruism presents an evolutionary paradox, as altruistic individuals are good for the group yet vulnerable to exploitation by selfish individuals. One mechanism that can effectively curtail selfishness within groups is punishment. Here, we show in an evolutionary game-theoretical model that punishment can effectively evolve and maintain high levels of altruism in the population, yet not all punishment strategies were equally virtuous. Unlike typical models of social evolution, we explicitly altered the extent to which individuals vary in their power over others, such that powerful individuals can more readily punish and escape the punishment of others. Two primary findings emerged. Under large power asymmetries, a powerful selfish minority maintained altruism of the masses. In contrast, increased symmetry of power among individuals produced a more egalitarian society held together by altruism and punishment carried out by the collective. These extremes are consistent with the coercive nature of the powerful elites in social insects and egalitarian mechanisms of punishment in humans such as coalitional enforcement and gossip. Our overall findings provide insights into the importance of oversight, the consequences to changes in the power structure of social systems, and the roots of hypocrisy and corruption in human and nonhuman animal societies.
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Affiliation(s)
- Omar Tonsi Eldakar
- Department of Biological Sciences, Nova Southeastern University, Fort Lauderdale, FL, USA
| | - J. Oliver Kammeyer
- Department of Writing, Literature, and Publishing, Emerson College, Boston, MA, USA
| | - Nikhil Nagabandi
- Department of Biological Sciences, Nova Southeastern University, Fort Lauderdale, FL, USA
| | - Andrew C. Gallup
- Department of Social and Behavioral Sciences, State University of New York Polytechnic Institute, Utica, NY, USA
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10
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An individual-level selection model for the apparent altruism exhibited by cellular slime moulds. J Biosci 2018. [DOI: 10.1007/s12038-018-9734-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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11
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Reid CR, Latty T. Collective behaviour and swarm intelligence in slime moulds. FEMS Microbiol Rev 2018; 40:798-806. [PMID: 28204482 DOI: 10.1093/femsre/fuw033] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 03/15/2016] [Accepted: 07/19/2016] [Indexed: 01/11/2023] Open
Abstract
The study of collective behaviour aims to understand how individual-level behaviours can lead to complex group-level patterns. Collective behaviour has primarily been studied in animal groups such as colonies of insects, flocks of birds and schools of fish. Although less studied, collective behaviour also occurs in microorganisms. Here, we argue that slime moulds are powerful model systems for solving several outstanding questions in collective behaviour. In particular, slime mould may hold the key to linking individual-level mechanisms to colony-level behaviours. Using well-established principles of collective animal behaviour as a framework, we discuss the extent to which slime mould collectives are comparable to animal groups, and we highlight some potentially fruitful areas for future research.
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Affiliation(s)
- Chris R Reid
- Department of Biological Sciences, Macquarie University, Sydney, NSW,Australia.,School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia
| | - Tanya Latty
- School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia
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12
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Votaw HR, Ostrowski EA. Stalk size and altruism investment within and among populations of the social amoeba. J Evol Biol 2017; 30:2017-2030. [DOI: 10.1111/jeb.13172] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Revised: 07/13/2017] [Accepted: 08/20/2017] [Indexed: 11/26/2022]
Affiliation(s)
- H. R. Votaw
- Department of Biology and Biochemistry University of Houston Houston TX USA
| | - E. A. Ostrowski
- Department of Biology and Biochemistry University of Houston Houston TX USA
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13
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Martínez-García R, Tarnita CE. Seasonality can induce coexistence of multiple bet-hedging strategies in Dictyostelium discoideum via storage effect. J Theor Biol 2017; 426:104-116. [PMID: 28536035 DOI: 10.1016/j.jtbi.2017.05.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2016] [Revised: 05/05/2017] [Accepted: 05/17/2017] [Indexed: 02/06/2023]
Abstract
The social amoeba Dictyostelium discoideum has been recently suggested as an example of bet-hedging in microbes. In the presence of resources, amoebae reproduce as unicellular organisms. Resource depletion, however, leads to a starvation phase in which the population splits between aggregators, which form a fruiting body made of a stalk and resistant spores, and non-aggregators, which remain as vegetative cells. Spores are favored when starvation periods are long, but vegetative cells can exploit resources in environments where food replenishes quickly. The investment in aggregators versus non-aggregators can therefore be understood as a bet-hedging strategy that evolves in response to stochastic starvation times. A genotype (or strategy) is defined by the balance between each type of cells. In this framework, if the ecological conditions on a patch are defined in terms of the mean starvation time (i.e. time between the onset of starvation and the arrival of a new food pulse), a single genotype dominates each environment, which is inconsistent with the huge genetic diversity observed in nature. Here we investigate whether seasonality, represented by a periodic, wet-dry alternation in the mean starvation times, allows the coexistence of several strategies in a single patch. We study this question in a non-spatial (well-mixed) setting in which different strains compete for a common pool of resources over a sequence of growth-starvation cycles. We find that seasonality induces a temporal storage effect that can promote the stable coexistence of multiple genotypes. Two conditions need to be met in our model. First, there has to be a temporal niche partitioning (two well-differentiated habitats within the year), which requires not only different mean starvation times between seasons but also low variance within each season. Second, each season's well-adapted strain has to grow and create a large enough population that permits its survival during the subsequent unfavorable season, which requires the number of growth-starvation cycles within each season to be sufficiently large. These conditions allow the coexistence of two bet-hedging strategies. Additional tradeoffs among life-history traits can expand the range of coexistence and increase the number of coexisting strategies, contributing toward explaining the genetic diversity observed in D. discoideum. Although focused on this cellular slime mold, our results are general and may be easily extended to other microbes.
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Affiliation(s)
- Ricardo Martínez-García
- Department of Ecology and Evolutionary Biology, Princeton University. Princeton NJ 08544, USA
| | - Corina E Tarnita
- Department of Ecology and Evolutionary Biology, Princeton University. Princeton NJ 08544, USA.
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14
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Barker JL, Bronstein JL, Friesen ML, Jones EI, Reeve HK, Zink AG, Frederickson ME. Synthesizing perspectives on the evolution of cooperation within and between species. Evolution 2017; 71:814-825. [PMID: 28071790 DOI: 10.1111/evo.13174] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Revised: 12/24/2016] [Accepted: 01/04/2017] [Indexed: 12/11/2022]
Abstract
Cooperation is widespread both within and between species, but are intraspecific and interspecific cooperation fundamentally similar or qualitatively different phenomena? This review evaluates this question, necessary for a general understanding of the evolution of cooperation. First, we outline three advantages of cooperation relative to noncooperation (acquisition of otherwise inaccessible goods and services, more efficient acquisition of resources, and buffering against variability), and predict when individuals should cooperate with a conspecific versus a heterospecific partner to obtain these advantages. Second, we highlight five axes along which heterospecific and conspecific partners may differ: relatedness and fitness feedbacks, competition and resource use, resource-generation abilities, relative evolutionary rates, and asymmetric strategy sets and outside options. Along all of these axes, certain asymmetries between partners are more common in, but not exclusive to, cooperation between species, especially complementary resource use and production. We conclude that cooperation within and between species share many fundamental qualities, and that differences between the two systems are explained by the various asymmetries between partners. Consideration of the parallels between intra- and interspecific cooperation facilitates application of well-studied topics in one system to the other, such as direct benefits within species and kin-selected cooperation between species, generating promising directions for future research.
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Affiliation(s)
- Jessica L Barker
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, 85721.,Current Address: Aarhus Institute of Advanced Studies, Aarhus University, 8000, Aarhus C, Denmark
| | - Judith L Bronstein
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, 85721
| | - Maren L Friesen
- Department of Plant Biology, Michigan State University, East Lansing, Michigan, 48824
| | - Emily I Jones
- Department of BioSciences, Rice University, Houston, Texas, 77005
| | - H Kern Reeve
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York, 14853
| | - Andrew G Zink
- Department of Biology, San Francisco State University, San Francisco, California, 94132
| | - Megan E Frederickson
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3B2, Canada
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15
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Affiliation(s)
- Laure Gallien
- Centre for Invasion Biology, Dept of Botany and Zoology; Stellenbosch Univ.; ZA-7602 Matieland South Africa
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16
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Gruenheit N, Parkinson K, Stewart B, Howie JA, Wolf JB, Thompson CRL. A polychromatic 'greenbeard' locus determines patterns of cooperation in a social amoeba. Nat Commun 2017; 8:14171. [PMID: 28120827 PMCID: PMC5288501 DOI: 10.1038/ncomms14171] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 12/06/2016] [Indexed: 12/30/2022] Open
Abstract
Cheaters disrupt cooperation by reaping the benefits without paying their fair share of associated costs. Cheater impact can be diminished if cooperators display a tag (‘greenbeard') and recognise and preferentially direct cooperation towards other tag carriers. Despite its popular appeal, the feasibility of such greenbeards has been questioned because the complex patterns of partner-specific cooperative behaviours seen in nature require greenbeards to come in different colours. Here we show that a locus (‘Tgr') of a social amoeba represents a polychromatic greenbeard. Patterns of natural Tgr locus sequence polymorphisms predict partner-specific patterns of cooperation by underlying variation in partner-specific protein–protein binding strength and recognition specificity. Finally, Tgr locus polymorphisms increase fitness because they help avoid potential costs of cooperating with incompatible partners. These results suggest that a polychromatic greenbeard can provide a key mechanism for the evolutionary maintenance of cooperation. Cooperation can be stabilized against exploitation if cooperators can reliably recognize each other. Here, Gruenheit and colleagues show that different alleles of the Tgr locus of the social amoeba Dictyostelium discoideum underlie the ability of different strains to recognize and cooperate with socially compatible individuals.
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Affiliation(s)
- Nicole Gruenheit
- Faculty of Biology, Medicine and Health, Department of Developmental Biology and Medicine, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Katie Parkinson
- Faculty of Biology, Medicine and Health, Department of Developmental Biology and Medicine, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Balint Stewart
- Faculty of Biology, Medicine and Health, Department of Developmental Biology and Medicine, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Jennifer A Howie
- Faculty of Biology, Medicine and Health, Department of Developmental Biology and Medicine, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
| | - Jason B Wolf
- Milner Centre for Evolution and Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
| | - Christopher R L Thompson
- Faculty of Biology, Medicine and Health, Department of Developmental Biology and Medicine, The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK
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17
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Abstract
ABSTRACT
Cooperation has been studied extensively across the tree of life, from eusociality in insects to social behavior in humans, but it is only recently that a social dimension has been recognized and extensively explored for microbes. Research into microbial cooperation has accelerated dramatically and microbes have become a favorite system because of their fast evolution, their convenience as lab study systems and the opportunity for molecular investigations. However, the study of microbes also poses significant challenges, such as a lack of knowledge and an inaccessibility of the ecological context (used here to include both the abiotic and the biotic environment) under which the trait deemed cooperative has evolved and is maintained. I review the experimental and theoretical evidence in support of the limitations of the study of social behavior in microbes in the absence of an ecological context. I discuss both the need and the opportunities for experimental investigations that can inform a theoretical framework able to reframe the general questions of social behavior in a clear ecological context and to account for eco-evolutionary feedback.
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Affiliation(s)
- Corina E. Tarnita
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
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18
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Zhang Z, Claessen D, Rozen DE. Understanding Microbial Divisions of Labor. Front Microbiol 2016; 7:2070. [PMID: 28066387 PMCID: PMC5174093 DOI: 10.3389/fmicb.2016.02070] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Accepted: 12/07/2016] [Indexed: 12/27/2022] Open
Abstract
Divisions of labor are ubiquitous in nature and can be found at nearly every level of biological organization, from the individuals of a shared society to the cells of a single multicellular organism. Many different types of microbes have also evolved a division of labor among its colony members. Here we review several examples of microbial divisions of labor, including cases from both multicellular and unicellular microbes. We first discuss evolutionary arguments, derived from kin selection, that allow divisions of labor to be maintained in the face of non-cooperative cheater cells. Next we examine the widespread natural variation within species in their expression of divisions of labor and compare this to the idea of optimal caste ratios in social insects. We highlight gaps in our understanding of microbial caste ratios and argue for a shift in emphasis from understanding the maintenance of divisions of labor, generally, to instead focusing on its specific ecological benefits for microbial genotypes and colonies. Thus, in addition to the canonical divisions of labor between, e.g., reproductive and vegetative tasks, we may also anticipate divisions of labor to evolve to reduce the costly production of secondary metabolites or secreted enzymes, ideas we consider in the context of streptomycetes. The study of microbial divisions of labor offers opportunities for new experimental and molecular insights across both well-studied and novel model systems.
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Affiliation(s)
- Zheren Zhang
- Institute of Biology, Leiden University Leiden, Netherlands
| | | | - Daniel E Rozen
- Institute of Biology, Leiden University Leiden, Netherlands
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19
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Martínez-García R, Tarnita CE. Lack of Ecological and Life History Context Can Create the Illusion of Social Interactions in Dictyostelium discoideum. PLoS Comput Biol 2016; 12:e1005246. [PMID: 27977666 PMCID: PMC5157950 DOI: 10.1371/journal.pcbi.1005246] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 11/14/2016] [Indexed: 12/13/2022] Open
Abstract
Studies of social microbes often focus on one fitness component (reproductive success within the social complex), with little information about or attention to other stages of the life cycle or the ecological context. This can lead to paradoxical results. The life cycle of the social amoeba Dictyostelium discoideum includes a multicellular stage in which not necessarily clonal amoebae aggregate upon starvation to form a possibly chimeric (genetically heterogeneous) fruiting body made of dead stalk cells and spores. The lab-measured reproductive skew in the spores of chimeras indicates strong social antagonism that should result in low genotypic diversity, which is inconsistent with observations from nature. Two studies have suggested that this inconsistency stems from the one-dimensional assessment of fitness (spore production) and that the solution lies in tradeoffs between multiple life-history traits, e.g.: spore size versus viability; and spore-formation (via aggregation) versus staying vegetative (as non-aggregated cells). We develop an ecologically-grounded, socially-neutral model (i.e. no social interactions between genotypes) for the life cycle of social amoebae in which we theoretically explore multiple non-social life-history traits, tradeoffs and tradeoff-implementing mechanisms. We find that spore production comes at the expense of time to complete aggregation, and, depending on the experimental setup, spore size and viability. Furthermore, experimental results regarding apparent social interactions within chimeric mixes can be qualitatively recapitulated under this neutral hypothesis, without needing to invoke social interactions. This allows for simple potential resolutions to the previously paradoxical results. We conclude that the complexities of life histories, including social behavior and multicellularity, can only be understood in the appropriate multidimensional ecological context, when considering all stages of the life cycle. Fitness in social microbes is often measured in terms of reproductive success in the social stage, with little regard to other stages of the life cycle (e.g. solitary) or to the ecological context. This approach can lead to seemingly paradoxical results that point to complex social interactions (e.g., social cheating) among individuals in the population. However, recent experimental studies in Dictyostelium discoideum, one of the most studied social microbes, have highlighted various tradeoffs among previously ignored non-social traits that should affect fitness. We develop an ecologically-motivated socially-neutral model for the life cycle of D. discoideum that combines these proposed traits and tradeoffs and proposes new ones to determine whether existing observations can be explained without the need to invoke social interactions. We confirm this expectation and conclude that the complexities of social behavior can only be understood in the appropriate ecological context, when considering a complete description of the life cycle.
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Affiliation(s)
- Ricardo Martínez-García
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton NJ, United States of America
| | - Corina E Tarnita
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton NJ, United States of America
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20
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Strassmann JE. Kin Discrimination in
Dictyostelium
Social Amoebae. J Eukaryot Microbiol 2016; 63:378-83. [DOI: 10.1111/jeu.12307] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 02/05/2016] [Accepted: 02/11/2016] [Indexed: 12/26/2022]
Affiliation(s)
- Joan E. Strassmann
- Department of Biology Washington University in St. Louis CB1137 St. Louis Missouri 63130‐4899
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21
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Epistasis between adults and larvae underlies caste fate and fitness in a clonal ant. Nat Commun 2015; 5:3363. [PMID: 24561920 DOI: 10.1038/ncomms4363] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Accepted: 01/31/2014] [Indexed: 12/24/2022] Open
Abstract
In social species, the phenotype and fitness of an individual depend in part on the genotype of its social partners. However, how these indirect genetic effects affect genotype fitness in competitive situations is poorly understood in animal societies. We therefore studied phenotypic plasticity and fitness of two clones of the ant Cerapachys biroi in monoclonal and chimeric colonies. Here we show that, while clone B has lower fitness in isolation, surprisingly, it consistently outcompetes clone A in chimeras. The reason is that, in chimeras, clone B produces more individuals specializing in reproduction rather than cooperative tasks, behaving like a facultative social parasite. A cross-fostering experiment shows that the proportion of these individuals depends on intergenomic epistasis between larvae and nursing adults, explaining the flexible allocation strategy of clone B. Our results suggest that intergenomic epistasis can be the proximate mechanism for social parasitism in ants, revealing striking analogies between social insects and social microbes.
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22
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Jack CN, Buttery N, Adu-Oppong B, Powers M, Thompson CR, Queller DC, Strassmann JE. Migration in the social stage of Dictyostelium discoideum amoebae impacts competition. PeerJ 2015; 3:e1352. [PMID: 26528414 PMCID: PMC4627915 DOI: 10.7717/peerj.1352] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Accepted: 10/05/2015] [Indexed: 11/25/2022] Open
Abstract
Interaction conditions can change the balance of cooperation and conflict in multicellular groups. After aggregating together, cells of the social amoeba Dictyostelium discoideum may migrate as a group (known as a slug) to a new location. We consider this migration stage as an arena for social competition and conflict because the cells in the slug may not be from a genetically homogeneous population. In this study, we examined the interplay of two seemingly diametric actions, the solitary action of kin recognition and the collective action of slug migration in D. discoideum, to more fully understand the effects of social competition on fitness over the entire lifecycle. We compare slugs composed of either genetically homogenous or heterogeneous cells that have migrated or remained stationary in the social stage of the social amoeba Dictyostelium discoideum. After migration of chimeric slugs, we found that facultative cheating is reduced, where facultative cheating is defined as greater contribution to spore relative to stalk than found for that clone in the clonal state. In addition our results support previous findings that competitive interactions in chimeras diminish slug migration distance. Furthermore, fruiting bodies have shorter stalks after migration, even accounting for cell numbers at that time. Taken together, these results show that migration can alleviate the conflict of interests in heterogeneous slugs. It aligns their interest in finding a more advantageous place for dispersal, where shorter stalks suffice, which leads to a decrease in cheating behavior.
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Affiliation(s)
- Chandra N. Jack
- Department of Plant Biology, Michigan State University, East Lansing, MI, United States of America
| | - Neil Buttery
- Department of Biology, Washington University, St. Louis, United States of America
| | - Boahemaa Adu-Oppong
- Department of Biology, Washington University, St. Louis, United States of America
| | - Michael Powers
- Department of Biosciences, Rice University, Houston, United States of America
| | | | - David C. Queller
- Department of Biology, Washington University, St. Louis, United States of America
| | - Joan E. Strassmann
- Department of Biology, Washington University, St. Louis, United States of America
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23
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Wolf JB, Howie JA, Parkinson K, Gruenheit N, Melo D, Rozen D, Thompson CRL. Fitness Trade-offs Result in the Illusion of Social Success. Curr Biol 2015; 25:1086-90. [PMID: 25819562 PMCID: PMC4406944 DOI: 10.1016/j.cub.2015.02.061] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Revised: 01/20/2015] [Accepted: 02/20/2015] [Indexed: 11/01/2022]
Abstract
Cooperation is ubiquitous across the tree of life, from simple microbes to the complex social systems of animals. Individuals cooperate by engaging in costly behaviors that can be exploited by other individuals who benefit by avoiding these associated costs. Thus, if successful exploitation of social partners during cooperative interactions increases relative fitness, then we expect selection to lead to the emergence of a single optimal winning strategy in which individuals maximize their gain from cooperation while minimizing their associated costs. Such social "cheating" appears to be widespread in nature, including in several microbial systems, but despite the fitness advantages favoring social cheating, populations tend to harbor significant variation in social success rather than a single optimal winning strategy. Using the social amoeba Dictyostelium discoideum, we provide a possible explanation for the coexistence of such variation. We find that genotypes typically designated as "cheaters" because they produce a disproportionate number of spores in chimeric fruiting bodies do not actually gain higher fitness as a result of this apparent advantage because they produce smaller, less viable spores than putative "losers." As a consequence of this trade-off between spore number and viability, genotypes with different spore production strategies, which give the appearance of differential social success, ultimately have similar realized fitness. These findings highlight the limitations of using single fitness proxies in evolutionary studies and suggest that interpreting social trait variation in terms of strategies like cheating or cooperating may be misleading unless these behaviors are considered in the context of the true multidimensional nature of fitness.
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Affiliation(s)
- Jason B Wolf
- Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
| | - Jennifer A Howie
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Katie Parkinson
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Nicole Gruenheit
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
| | - Diogo Melo
- Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil
| | - Daniel Rozen
- Institute of Biology, Leiden University, Sylvius Laboratory, Sylviusweg 72, PO Box 9505, 2300 RA Leiden, the Netherlands
| | - Christopher R L Thompson
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
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24
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Precarious development: the uncertain social life of cellular slime molds. Proc Natl Acad Sci U S A 2015; 112:2639-40. [PMID: 25713343 DOI: 10.1073/pnas.1500708112] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
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25
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Fitness tradeoffs between spores and nonaggregating cells can explain the coexistence of diverse genotypes in cellular slime molds. Proc Natl Acad Sci U S A 2015; 112:2776-81. [PMID: 25605926 DOI: 10.1073/pnas.1424242112] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cellular slime molds, including the well-studied Dictyostelium discoideum, are amoebae whose life cycle includes both a single-cellular and a multicellular stage. To achieve the multicellular stage, individual amoebae aggregate upon starvation to form a fruiting body made of dead stalk cells and reproductive spores, a process that has been described in terms of cooperation and altruism. When amoebae aggregate they do not perfectly discriminate against nonkin, leading to chimeric fruiting bodies. Within chimeras, complex interactions among genotypes have been documented, which should theoretically reduce genetic diversity. This is however inconsistent with the great diversity of genotypes found in nature. Recent work has shown that a little-studied component of D. discoideum fitness--the loner cells that do not participate in the aggregation--can be selected for depending on environmental conditions and that, together with the spores, they could represent a bet-hedging strategy. We suggest that in all cellular slime molds the existence of loners could resolve the apparent diversity paradox in two ways. First, if loners are accounted for, then apparent genotypic skew in the spores of chimeras could simply be the result of different investments into spores versus loners. Second, in an ecosystem with multiple local environments differing in their food recovery characteristics and connected globally via weak-to-moderate dispersal, coexistence of multiple genotypes can occur. Finally, we argue that the loners make it impossible to define altruistic behavior, winners or losers, without a clear description of the ecology.
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26
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Li SI, Buttery NJ, Thompson CRL, Purugganan MD. Sociogenomics of self vs. non-self cooperation during development of Dictyostelium discoideum. BMC Genomics 2014; 15:616. [PMID: 25048306 PMCID: PMC4118049 DOI: 10.1186/1471-2164-15-616] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 07/14/2014] [Indexed: 12/21/2022] Open
Abstract
Background Dictyostelium discoideum, a microbial model for social evolution, is known to distinguish self from non-self and show genotype-dependent behavior during chimeric development. Aside from a small number of cell-cell recognition genes, however, little is known about the genetic basis of self/non-self recognition in this species. Based on the key hypothesis that there should be differential expression of genes if D. discoideum cells were interacting with non-clone mates, we performed transcriptomic profiling study in this species during clonal vs. chimeric development. The transcriptomic profiles of D. discoideum cells in clones vs. different chimeras were compared at five different developmental stages using a customized microarray. Effects of chimerism on global transcriptional patterns associated with social interactions were observed. Results We find 1,759 genes significantly different between chimera and clone, 1,144 genes associated significant strain differences, and 6,586 genes developmentally regulated over time. Principal component analysis showed a small amount of the transcriptional variance to chimerism-related factors (Chimerism: 0.18%, Chimerism × Timepoint: 0.03%). There are 162 genes specifically regulated under chimeric development, with continuous small differences between chimera vs. clone over development. Almost 60% of chimera-associated differential genes were differentially expressed at the 4 h aggregate stage, which corresponds to the initial transition of D. discoideum from solitary life to a multicellular phase. Conclusions A relatively small proportion of over-all variation in gene expression is explained by differences between chimeric and clonal development. The relatively small modifications in gene expression associated with chimerism is compatible with the high level of cooperation observed among different strains of D. discoideum; cells of distinct genetic backgrounds will co-aggregate indiscriminately and co-develop into fruiting bodies. Chimeric development may involve re-programming of the transcriptome through small modifications of the developmental genetic network, which may also indicate that response to social interaction involves many genes with individually small transcriptional effect. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-616) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | - Michael D Purugganan
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY, 10003, USA.
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27
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Sathe S, Khetan N, Nanjundiah V. Interspecies and intraspecies interactions in social amoebae. J Evol Biol 2013; 27:349-62. [PMID: 24341405 DOI: 10.1111/jeb.12298] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Accepted: 11/12/2013] [Indexed: 11/29/2022]
Abstract
The stable co-existence of individuals of different genotypes and reproductive division of labour within heterogeneous groups are issues of fundamental interest from the viewpoint of evolution. Cellular slime moulds are convenient organisms in which to address both issues. Strains of a species co-occur, as do different species; social groups are often genetically heterogeneous. Intra- and interspecies 1 : 1 mixes of wild isolates of Dictyostelium giganteum and D. purpureum form chimaeric aggregates, following which they segregate to varying extents. Intraspecies aggregates develop in concert and give rise to chimaeric fruiting bodies that usually contain more spores (reproductives) of one component than the other. Reproductive skew and variance in the proportion of reproductives are positively correlated. Interspecies aggregates exhibit almost complete sorting; most spores in a fruiting body come from a single species. Between strains, somatic compatibility correlates weakly with sexual compatibility. It is highest within clones, lower between strains of a species and lowest between strains of different species. Trade-offs among fitness-related traits (between compatible strains), sorting out (between incompatible strains) and avoidance (between species) appear to lie behind coexistence.
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Affiliation(s)
- S Sathe
- Centre for Ecological Sciences, Indian Institute of Science, Bangalore, India; Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India
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28
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Smith J, Van Dyken JD, Velicer GJ. Nonadaptive processes can create the appearance of facultative cheating in microbes. Evolution 2013; 68:816-26. [PMID: 24171718 DOI: 10.1111/evo.12306] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Accepted: 10/22/2013] [Indexed: 10/26/2022]
Abstract
Adaptations to social life may take the form of facultative cheating, in which organisms cooperate with genetically similar individuals but exploit others. Consistent with this possibility, many strains of social microbes like Myxococcus bacteria and Dictyostelium amoebae have equal fitness in single-genotype social groups but outcompete other strains in mixed-genotype groups. Here we show that these observations are also consistent with an alternative, nonadaptive scenario: kin selection-mutation balance under local competition. Using simple mathematical models, we show that deleterious mutations that reduce competitiveness within social groups (growth rate, e.g.) without affecting group productivity can create fitness effects that are only expressed in the presence of other strains. In Myxococcus, mutations that delay sporulation may strongly reduce developmental competitiveness. Deleterious mutations are expected to accumulate when high levels of kin selection relatedness relax selection within groups. Interestingly, local resource competition can create nonzero "cost" and "benefit" terms in Hamilton's rule even in the absence of any cooperative trait. Our results show how deleterious mutations can play a significant role even in organisms with large populations and highlight the need to test evolutionary causes of social competition among microbes.
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Affiliation(s)
- Jeff Smith
- Department of Biology, Washington University in St. Louis, Saint Louis, Missouri.
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29
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Ghoul M, Griffin AS, West SA. Toward an evolutionary definition of cheating. Evolution 2013; 68:318-31. [PMID: 24131102 DOI: 10.1111/evo.12266] [Citation(s) in RCA: 111] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 08/27/2013] [Indexed: 12/17/2022]
Abstract
The term "cheating" is used in the evolutionary and ecological literature to describe a wide range of exploitative or deceitful traits. Although many find this a useful short hand, others have suggested that it implies cognitive intent in a misleading way, and is used inconsistently. We provide a formal justification of the use of the term "cheat" from the perspective of an individual as a maximizing agent. We provide a definition for cheating that can be applied widely, and show that cheats can be broadly classified on the basis of four distinctions: (i) whether cooperation is an option; (ii) whether deception is involved; (iii) whether members of the same or different species are cheated; and (iv) whether the cheat is facultative or obligate. Our formal definition and classification provide a framework that allow us to resolve and clarify a number of issues, regarding the detection and evolutionary consequences of cheating, as well as illuminating common principles and similarities in the underlying selection pressures.
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Affiliation(s)
- Melanie Ghoul
- Department of Zoology, Oxford University, Oxford, OX1 3PS, United Kingdom.
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30
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The rate and effects of spontaneous mutation on fitness traits in the social amoeba, Dictyostelium discoideum. G3-GENES GENOMES GENETICS 2013; 3:1115-27. [PMID: 23665876 PMCID: PMC3704240 DOI: 10.1534/g3.113.005934] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
We performed a mutation accumulation (MA) experiment in the social amoeba Dictyostelium discoideum to estimate the rate and distribution of effects of spontaneous mutations affecting eight putative fitness traits. We found that the per-generation mutation rate for most fitness components is 0.0019 mutations per haploid genome per generation or larger. This rate is an order of magnitude higher than estimates for fitness components in the unicellular eukaryote Saccharomyces cerevisiae, even though the base-pair substitution rate is two orders of magnitude lower. The high rate of fitness-altering mutations observed in this species may be partially explained by a large mutational target relative to S. cerevisiae. Fitness-altering mutations also may occur primarily at simple sequence repeats, which are common throughout the genome, including in coding regions, and may represent a target that is particularly likely to give fitness effects upon mutation. The majority of mutations had deleterious effects on fitness, but there was evidence for a substantial fraction, up to 40%, being beneficial for some of the putative fitness traits. Competitive ability within the multicellular slug appears to be under weak directional selection, perhaps reflecting the fact that slugs are sometimes, but not often, comprised of multiple clones in nature. Evidence for pleiotropy among fitness components across MA lines was absent, suggesting that mutations tend to act on single fitness components.
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31
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Abstract
Dictyostelium has become a model organism for the study of social evolution because of the stage in its life cycle where thousands of independent amoebae together form a fruiting body. Some individuals die to form a stalk that holds aloft the remaining cells for dispersal to new environments as spores. Different genotypes can aggregate together, creating opportunities for exploitation by cheaters that contribute a smaller proportion of cells to the stalk. Clustering of genotypes into separate fruiting bodies reduces the opportunities for cheating. Some genotypes achieve this by segregating after aggregation. Here we describe techniques for assaying cheating and segregation in D. discoideum. We cover how to grow and maintain cells, fluorescently label genotypes, design experiments for accuracy and precision, calculate fitness and segregation, and interpret the results.
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32
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Hollis B. Rapid antagonistic coevolution between strains of the social amoeba Dictyostelium discoideum. Proc Biol Sci 2012; 279:3565-71. [PMID: 22719037 DOI: 10.1098/rspb.2012.0975] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Social groups face a fundamental problem of overcoming selfish individuals capable of destroying cooperation. In the social amoeba Dictyostelium discoideum, there is evidence that some clones ('cheaters') contribute disproportionately to the viable spores in a fruiting body while avoiding the dead stalk cell fate. It remains unclear, however, whether this cheating is actually the product of selection. Here, I report the results of an experimental evolution study designed to test whether clones of D. discoideum will evolve resistance to cheating in the laboratory with genetic variation created only through spontaneous mutation. Two strains, one green fluorescent protein (GFP)-labelled and one wild-type, were allowed to grow and develop together before the wild-type strain was removed and replaced with a naïve strain evolving in parallel. Over the course of 10 social generations, the GFP-labelled strain reliably increased its representation in the spores relative to control populations that had never experienced the competitor. This competitive advantage extended to the non-social, vegetative growth portion of the life cycle, but not to pairwise competition with two other strains. These results indicate strong antagonism between strains, mediated by ample mutational variation for cheating and also suggest that arms races between strains in the wild may be common.
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Affiliation(s)
- Brian Hollis
- Department of Ecology and Evolution, University of Lausanne, Biophore, 1015 Lausanne, Switzerland.
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33
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Abstract
Recognition of relatives is important in microbes because they perform many behaviors that have costs to the actor while benefiting neighbors. Microbes cooperate for nourishment, movement, virulence, iron acquisition, protection, quorum sensing, and production of multicellular biofilms or fruiting bodies. Helping others is evolutionarily favored if it benefits others who share genes for helping, as specified by kin selection theory. If microbes generally find themselves in clonal patches, then no special means of discrimination is necessary. Much real discrimination is actually of kinds, not kin, as in poison-antidote systems, such as bacteriocins, in which cells benefit their own kind by poisoning others, and in adhesion systems, in which cells of the same kind bind together. These behaviors can elevate kinship generally and make cooperation easier to evolve and maintain.
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Affiliation(s)
- Joan E Strassmann
- Department of Ecology and Evolutionary Biology, Rice University, Houston, Texas 77005, USA.
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34
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Strassmann JE, Queller DC. Evolution of cooperation and control of cheating in a social microbe. Proc Natl Acad Sci U S A 2011; 108 Suppl 2:10855-62. [PMID: 21690338 PMCID: PMC3131822 DOI: 10.1073/pnas.1102451108] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Much of what we know about the evolution of altruism comes from animals. Here, we show that studying a microbe has yielded unique insights, particularly in understanding how social cheaters are controlled. The social stage of Dictylostelium discoideum occurs when the amoebae run out of their bacterial prey and aggregate into a multicellular, motile slug. This slug forms a fruiting body in which about a fifth of cells die to form a stalk that supports the remaining cells as they form hardy dispersal-ready spores. Because this social stage forms from aggregation, it is analogous to a social group, or a chimeric multicellular organism, and is vulnerable to internal conflict. Advances in cell labeling, microscopy, single-gene knockouts, and genomics, as well as the results of decades of study of D. discoideum as a model for development, allow us to explore the genetic basis of social contests and control of cheaters in unprecedented detail. Cheaters are limited from exploiting other clones by high relatedness, kin discrimination, pleiotropy, noble resistance, and lottery-like role assignment. The active nature of these limits is reflected in the elevated rates of change in social genes compared with nonsocial genes. Despite control of cheaters, some conflict is still expressed in chimeras, with slower movement of slugs, slightly decreased investment in stalk compared with spore cells, and differential contributions to stalk and spores. D. discoideum is rapidly becoming a model system of choice for molecular studies of social evolution.
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Affiliation(s)
- Joan E Strassmann
- Ecology and Evolutionary Biology, Rice University, Houston, TX 77005, USA.
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35
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Parkinson K, Buttery NJ, Wolf JB, Thompson CRL. A simple mechanism for complex social behavior. PLoS Biol 2011; 9:e1001039. [PMID: 21468302 PMCID: PMC3066132 DOI: 10.1371/journal.pbio.1001039] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Accepted: 02/18/2011] [Indexed: 11/19/2022] Open
Abstract
The evolution of cooperation is a paradox because natural selection should favor exploitative individuals that avoid paying their fair share of any costs. Such conflict between the self-interests of cooperating individuals often results in the evolution of complex, opponent-specific, social strategies and counterstrategies. However, the genetic and biological mechanisms underlying complex social strategies, and therefore the evolution of cooperative behavior, are largely unknown. To address this dearth of empirical data, we combine mathematical modeling, molecular genetic, and developmental approaches to test whether variation in the production of and response to social signals is sufficient to generate the complex partner-specific social success seen in the social amoeba Dictyostelium discoideum. Firstly, we find that the simple model of production of and response to social signals can generate the sort of apparent complex changes in social behavior seen in this system, without the need for partner recognition. Secondly, measurements of signal production and response in a mutant with a change in a single gene that leads to a shift in social behavior provide support for this model. Finally, these simple measurements of social signaling can also explain complex patterns of variation in social behavior generated by the natural genetic diversity found in isolates collected from the wild. Our studies therefore demonstrate a novel and elegantly simple underlying mechanistic basis for natural variation in complex social strategies in D. discoideum. More generally, they suggest that simple rules governing interactions between individuals can be sufficient to generate a diverse array of outcomes that appear complex and unpredictable when those rules are unknown. Despite the appearance of cooperation in nature, selection should often favor exploitative individuals who perform less of any cooperative behaviors while maintaining the benefits accrued from the cooperative behavior of others. This conflict of interest among cooperating individuals can lead to the evolution of complex social strategies that depend on the identity (e.g. genotype or strategy) of the individuals with whom you interact. The social amoeba Dictyostelium discoideum provides a compelling model for studying such “partner specific” conflict and cooperation. Upon starvation, free-living amoebae aggregate and form a fruiting body composed of dead stalk cells and hardy spores. Different genotypes will aggregate to produce chimeric fruiting bodies, resulting in potential social conflict over who will contribute to the reproductive sporehead and who will “sacrifice” themselves to produce the dead stalk. The outcomes of competitive interactions in chimera appear complex, with social success being strongly partner specific. Here we propose a simple mechanism to explain social strategies in D. discoideum, based on the production of and response to stalk-inducing factors, the social signals that determine whether cells become stalk or spore. Indeed, measurements of signal production and response can predict social behavior of different strains, thus demonstrating a novel and elegantly simple underlying mechanistic basis for natural variation in complex facultative social strategies. This suggests that simple social rules can be sufficient to generate a diverse array of behavioral outcomes that appear complex and unpredictable when those rules are unknown.
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Affiliation(s)
- Katie Parkinson
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Neil J. Buttery
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Jason B. Wolf
- Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom
- * E-mail: (JBW); (CRLT)
| | - Christopher R. L. Thompson
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
- * E-mail: (JBW); (CRLT)
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Nanjundiah V, Sathe S. Social selection and the evolution of cooperative groups: The example of the cellular slime moulds. Integr Biol (Camb) 2011; 3:329-42. [PMID: 21264374 DOI: 10.1039/c0ib00115e] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Vidyanand Nanjundiah
- Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560012, India.
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Brännström A, Gross T, Blasius B, Dieckmann U. Consequences of fluctuating group size for the evolution of cooperation. J Math Biol 2010; 63:263-81. [PMID: 20957372 DOI: 10.1007/s00285-010-0367-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 08/16/2010] [Indexed: 11/28/2022]
Abstract
Studies of cooperation have traditionally focused on discrete games such as the well-known prisoner's dilemma, in which players choose between two pure strategies: cooperation and defection. Increasingly, however, cooperation is being studied in continuous games that feature a continuum of strategies determining the level of cooperative investment. For the continuous snowdrift game, it has been shown that a gradually evolving monomorphic population may undergo evolutionary branching, resulting in the emergence of a defector strategy that coexists with a cooperator strategy. This phenomenon has been dubbed the 'tragedy of the commune'. Here we study the effects of fluctuating group size on the tragedy of the commune and derive analytical conditions for evolutionary branching. Our results show that the effects of fluctuating group size on evolutionary dynamics critically depend on the structure of payoff functions. For games with additively separable benefits and costs, fluctuations in group size make evolutionary branching less likely, and sufficiently large fluctuations in group size can always turn an evolutionary branching point into a locally evolutionarily stable strategy. For games with multiplicatively separable benefits and costs, fluctuations in group size can either prevent or induce the tragedy of the commune. For games with general interactions between benefits and costs, we derive a general classification scheme based on second derivatives of the payoff function, to elucidate when fluctuations in group size help or hinder cooperation.
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Affiliation(s)
- Ake Brännström
- Department of Mathematics and Mathematical Statistics, Umeå University, 90187, Umeå, Sweden.
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Sathe S, Kaushik S, Lalremruata A, Aggarwal RK, Cavender JC, Nanjundiah V. Genetic heterogeneity in wild isolates of cellular slime mold social groups. MICROBIAL ECOLOGY 2010; 60:137-148. [PMID: 20179919 DOI: 10.1007/s00248-010-9635-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2009] [Accepted: 12/26/2009] [Indexed: 05/28/2023]
Abstract
This study addresses the issues of spatial distribution, dispersal, and genetic heterogeneity in social groups of the cellular slime molds (CSMs). The CSMs are soil amoebae with an unusual life cycle that consists of alternating solitary and social phases. Because the social phase involves division of labor with what appears to be an extreme form of "altruism", the CSMs raise interesting evolutionary questions regarding the origin and maintenance of sociality. Knowledge of the genetic structure of social groups in the wild is necessary for answering these questions. We confirm that CSMs are widespread in undisturbed forest soil from South India. They are dispersed over long distances via the dung of a variety of large mammals. Consistent with this mode of dispersal, most social groups in the two species examined for detailed study, Dictyostelium giganteum and Dictyostelium purpureum, are multi-clonal.
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Affiliation(s)
- Santosh Sathe
- Centre for Ecological Sciences, Indian Institute of Science, Bangalore, India.
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39
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Buttery NJ, Thompson CRL, Wolf JB. Complex genotype interactions influence social fitness during the developmental phase of the social amoeba Dictyostelium discoideum. J Evol Biol 2010; 23:1664-71. [PMID: 20546090 DOI: 10.1111/j.1420-9101.2010.02032.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
When individuals interact, phenotypic variation can be partitioned into direct genetic effects (DGEs) of the individuals' own genotypes, indirect genetic effects (IGEs) of their social partners' genotypes and epistatic interactions between the genotypes of interacting individuals ('genotype-by-genotype (GxG) epistasis'). These components can all play important roles in evolutionary processes, but few empirical studies have examined their importance. The social amoeba Dictyostelium discoideum provides an ideal system to measure these effects during social interactions and development. When starved, free-living amoebae aggregate and differentiate into a multicellular fruiting body with a dead stalk that holds aloft viable spores. By measuring interactions among a set of natural strains, we quantify DGEs, IGEs and GxG epistasis affecting spore formation. We find that DGEs explain most of the phenotypic variance (57.6%) whereas IGEs explain a smaller (13.3%) but highly significant component. Interestingly, GxG epistasis explains nearly a quarter of the variance (23.0%), highlighting the complex nature of genotype interactions. These results demonstrate the large impact that social interactions can have on development and suggest that social effects should play an important role in developmental evolution in this system.
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Affiliation(s)
- N J Buttery
- Faculty of Life Sciences, The University of Manchester, Manchester, UK
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40
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Parrinello N. Has innate immunity evolved through different routes? Phys Life Rev 2010; 7:83-4; discussion 85-7. [DOI: 10.1016/j.plrev.2010.01.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Accepted: 01/12/2010] [Indexed: 10/20/2022]
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41
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Jiricny N, Diggle SP, West SA, Evans BA, Ballantyne G, Ross-Gillespie A, Griffin AS. Fitness correlates with the extent of cheating in a bacterium. J Evol Biol 2010; 23:738-47. [PMID: 20210835 DOI: 10.1111/j.1420-9101.2010.01939.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
There is growing awareness of the importance of cooperative behaviours in microbial communities. Empirical support for this insight comes from experiments using mutant strains, termed 'cheats', which exploit the cooperative behaviour of wild-type strains. However, little detailed work has gone into characterising the competitive dynamics of cooperative and cheating strains. We test three specific predictions about the fitness consequences of cheating to different extents by examining the production of the iron-scavenging siderophore molecule, pyoverdin, in the bacterium Pseudomonas aeruginosa. We create a collection of mutants that differ in the amount of pyoverdin that they produce (from 1% to 96% of the production of paired wild types) and demonstrate that these production levels correlate with both gene activity and the ability to bind iron. Across these mutants, we found that (1) when grown in a mixed culture with a cooperative wild-type strain, the relative fitness of a mutant is negatively correlated with the amount of pyoverdin that it produces; (2) the absolute and relative fitness of the wild-type strain in the mixed culture is positively correlated with the amount of pyoverdin that the mutant produces; and (3) when grown in a monoculture, the absolute fitness of the mutant is positively correlated with the amount of pyoverdin that it produces. Overall, we demonstrate that cooperative pyoverdin production is exploitable and illustrate how variation in a social behaviour determines fitness differently, depending on the social environment.
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Affiliation(s)
- N Jiricny
- Department of Zoology, Oxford University, Oxford, UK
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Zhang QG, Buckling A, Ellis RJ, Godfray HCJ. COEVOLUTION BETWEEN COOPERATORS AND CHEATS IN A MICROBIAL SYSTEM. Evolution 2009; 63:2248-56. [DOI: 10.1111/j.1558-5646.2009.00708.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Buttery NJ, Rozen DE, Wolf JB, Thompson CRL. Quantification of social behavior in D. discoideum reveals complex fixed and facultative strategies. Curr Biol 2009; 19:1373-7. [PMID: 19631539 DOI: 10.1016/j.cub.2009.06.058] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2009] [Revised: 06/17/2009] [Accepted: 06/17/2009] [Indexed: 11/25/2022]
Abstract
Understanding the maintenance of cooperation requires an understanding of the nature of cheaters and the strategies used to mitigate their effects. However, it is often difficult to determine how cheating or differential social success has arisen. For example, cheaters may employ different strategies (e.g., fixed and facultative), whereas other causes of unequal fitness in social situations can result in winners and losers without cheating. To address these problems, we quantified the social success of naturally occurring genotypes of Dictyostelium discoideum during the formation of chimeric fruiting bodies, consisting of dead stalk cells and viable spores. We demonstrate that an apparent competitive dominance hierarchy of spore formation in chimera is partly due to a fixed strategy where genotypes exhibit dramatically different spore allocations. However, we also find complex, variable facultative strategies, where genotypes change their allocation in chimera. By determining the magnitude and direction of these changes, we partition facultative cheating into two forms: (1) promotion of individual fitness through selfish behaviour ("self-promotion") and (2) coercion of other genotypes to act cooperatively. Our results demonstrate and define social interactions between D. discoideum isolates, thus providing a conceptual framework for the study of the genetic mechanisms that underpin social evolution.
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Affiliation(s)
- Neil J Buttery
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Rd., Manchester M13 9PT, UK
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Gilbert OM, Queller DC, Strassmann JE. Discovery of a large clonal patch of a social amoeba: implications for social evolution. Mol Ecol 2009; 18:1273-81. [PMID: 19243508 DOI: 10.1111/j.1365-294x.2009.04108.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Owen M Gilbert
- Department of Ecology and Evolutionary Biology, Rice University, Houston, TX 77005, USA.
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45
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Ostrowski EA, Katoh M, Shaulsky G, Queller DC, Strassmann JE. Kin discrimination increases with genetic distance in a social amoeba. PLoS Biol 2009; 6:e287. [PMID: 19067487 PMCID: PMC2586364 DOI: 10.1371/journal.pbio.0060287] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2008] [Accepted: 10/10/2008] [Indexed: 12/04/2022] Open
Abstract
In the social amoeba Dictyostelium discoideum, thousands of cells aggregate upon starvation to form a multicellular fruiting body, and approximately 20% of them die to form a stalk that benefits the others. The aggregative nature of multicellular development makes the cells vulnerable to exploitation by cheaters, and the potential for cheating is indeed high. Cells might avoid being victimized if they can discriminate among individuals and avoid those that are genetically different. We tested how widely social amoebae cooperate by mixing isolates from different localities that cover most of their natural range. We show here that different isolates partially exclude one another during aggregation, and there is a positive relationship between the extent of this exclusion and the genetic distance between strains. Our findings demonstrate that D. discoideum cells co-aggregate more with genetically similar than dissimilar individuals, suggesting the existence of a mechanism that discerns the degree of genetic similarity between individuals in this social microorganism. In social amoebae such as Dictyostelium discoideum, cells aggregate to form a multicellular slug that migrates and then forms a fruiting body, which contains live spores (which go on to make new amoebae) and dead stalk cells. Unlike animals where all the cells descend from one fertilized egg, social amoeba fruiting bodies can contain cells with different genotypes. This potential for chimerism creates a conceptual problem in that “cheater” cells could arise that preferentially become reproductive spores and force the victims to become stalk cells and die. One way that amoebae could avoid being cheated is if they recognize and preferentially aggregate with genetically similar cells while avoiding genetically distant cells—a process called kin discrimination. We tested whether cells of D. discoideum could discriminate in this way. We mixed cells from genetically distinct strains and found that they segregate during multicellular development. The degree of segregation increases in a graded fashion with the genetic distance between strains. Our results demonstrate the existence of kin discrimination in D. discoideum, an ability that is likely to reduce the potential for cheating and ensure that the death of the stalk cells provides a fitness advantage to related individuals. Genetically based discrimination in social amoebae may help these cells to avoid cheaters that take advantage of their altruistic behavior.
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Affiliation(s)
- Elizabeth A Ostrowski
- Department of Ecology and Evolutionary Biology, Rice University, Houston, Texas, USA.
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Abstract
When confronted with starvation, the amoebae of Dictyostelium discoideum initiate a developmental process that begins with cell aggregation and ends with a ball of spores supported on a stalk. Spores live and stalk cells die. Because the multicellular organism is produced by cell aggregation and not by growth and division of a single cell, genetically diverse amoebae may enter an aggregate and, if one lineage has a capacity to avoid the stalk cell fate, it may have a selective advantage. Such cheater mutants have been found among wild isolates and created in laboratory strains. The mutants raise a number of questions--how did such a cooperative system evolve in the face of cheating? What is the basis of self recognition? What genes are involved? How is cheating constrained? This review summarizes the results of studies on the social behavior of Dictyostelium and its relatives, including the familiar asexual developmental cycle and the lesser known, but puzzling, sexual cycle.
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Affiliation(s)
- Gad Shaulsky
- Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.
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47
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West SA, Diggle SP, Buckling A, Gardner A, Griffin AS. The Social Lives of Microbes. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2007. [DOI: 10.1146/annurev.ecolsys.38.091206.095740] [Citation(s) in RCA: 529] [Impact Index Per Article: 31.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Stuart A. West
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom; ,
| | - Stephen P. Diggle
- Institute of Infection, Immunity & Inflammation, Center for Biomolecular Sciences, University of Nottingham, Nottingham NG7 2RD, United Kingdom;
| | - Angus Buckling
- Department of Zoology, Oxford University, Oxford OX1 3PS, United Kingdom;
| | - Andy Gardner
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom; ,
- St. John's College, Oxford University, Oxford OX1 3JP, United Kingdom;
| | - Ashleigh S. Griffin
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom; ,
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Gilbert OM, Foster KR, Mehdiabadi NJ, Strassmann JE, Queller DC. High relatedness maintains multicellular cooperation in a social amoeba by controlling cheater mutants. Proc Natl Acad Sci U S A 2007; 104:8913-7. [PMID: 17496139 PMCID: PMC1885602 DOI: 10.1073/pnas.0702723104] [Citation(s) in RCA: 175] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Indexed: 11/18/2022] Open
Abstract
The control of cheating is important for understanding major transitions in evolution, from the simplest genes to the most complex societies. Cooperative systems can be ruined if cheaters that lower group productivity are able to spread. Kin-selection theory predicts that high genetic relatedness can limit cheating, because separation of cheaters and cooperators limits opportunities to cheat and promotes selection against low-fitness groups of cheaters. Here, we confirm this prediction for the social amoeba Dictyostelium discoideum; relatedness in natural wild groups is so high that socially destructive cheaters should not spread. We illustrate in the laboratory how high relatedness can control a mutant that would destroy cooperation at low relatedness. Finally, we demonstrate that, as predicted, mutant cheaters do not normally harm cooperation in a natural population. Our findings show how altruism is preserved from the disruptive effects of such mutant cheaters and how exceptionally high relatedness among cells is important in promoting the cooperation that underlies multicellular development.
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Affiliation(s)
- Owen M Gilbert
- Department of Ecology and Evolutionary Biology, Rice University, MS 170, 6100 Main Street, Houston, TX 77005, USA.
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Abstract
Microorganisms communicate and cooperate to perform a wide range of multicellular behaviours, such as dispersal, nutrient acquisition, biofilm formation and quorum sensing. Microbiologists are rapidly gaining a greater understanding of the molecular mechanisms involved in these behaviours, and the underlying genetic regulation. Such behaviours are also interesting from the perspective of social evolution - why do microorganisms engage in these behaviours given that cooperative individuals can be exploited by selfish cheaters, who gain the benefit of cooperation without paying their share of the cost? There is great potential for interdisciplinary research in this fledgling field of sociomicrobiology, but a limiting factor is the lack of effective communication of social evolution theory to microbiologists. Here, we provide a conceptual overview of the different mechanisms through which cooperative behaviours can be stabilized, emphasizing the aspects most relevant to microorganisms, the novel problems that microorganisms pose and the new insights that can be gained from applying evolutionary theory to microorganisms.
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Affiliation(s)
- Stuart A West
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, King's Buildings, Edinburgh, EH9 3JT, UK.
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50
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MacWilliams H, Doquang K, Pedrola R, Dollman G, Grassi D, Peis T, Tsang A, Ceccarelli A. A retinoblastoma ortholog controls stalk/spore preference in Dictyostelium. Development 2006; 133:1287-97. [PMID: 16495312 DOI: 10.1242/dev.02287] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We describe rblA, the Dictyostelium ortholog of the retinoblastoma susceptibility gene Rb. In the growth phase, rblA expression is correlated with several factors that lead to 'preference' for the spore pathway. During multicellular development, expression increases 200-fold in differentiating spores. rblA-null strains differentiate stalk cells and spores normally, but in chimeras with wild type, the mutant shows a strong preference for the stalk pathway. rblA-null cells are hypersensitive to the stalk morphogen DIF, suggesting that rblA normally suppresses the DIF response in cells destined for the spore pathway. rblA overexpression during growth leads to G1 arrest, but as growing Dictyostelium are overwhelmingly in G2 phase, rblA does not seem to be important in the normal cell cycle. rblA-null cells show reduced cell size and a premature growth-development transition; the latter appears anomalous but may reflect selection pressures acting on social ameba.
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Affiliation(s)
- Harry MacWilliams
- Biozentrum der Ludwig-Maximilians-Universität, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany.
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