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Zhang L, Hood GR, Carroo I, Ott JR, Egan SP. Context-Dependent Reproductive Isolation: Host Plant Variability Drives Fitness of Hybrid Herbivores. Am Nat 2021; 197:732-739. [PMID: 33989147 DOI: 10.1086/714139] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractThe role of divergent selection between alternative environments in promoting reproductive isolation (RI) between lineages is well recognized. However, most studies view each divergent environment as homogenous, thereby overlooking the potential role within-environment variation plays in RI between differentiating lineages. Here, we test the importance of microenvironmental variation in RI by using individual trees of two host plants, each harboring locally adapted populations of the cynipid wasp Belonocnema treatae. We compared the fitness surrogate (survival) of offspring from hybrid crosses with resident crosses across individual trees on each of two primary host plants, Quercus virginiana and Q. geminata. We found evidence of weak hybrid inviability between host-associated lineages of B. treatae despite strong genomic differentiation. However, averaging across environments masked great variation in hybrid fitness on individual trees, where hybrids performed worse than, equal to, or better than residents. Thus, considering the environmental context of hybridization is critical to improving the predictability of divergence under variable selection.
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2
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Zhang YM, Egan SP, Driscoe AL, Ott JR. One hundred and sixty years of taxonomic confusion resolved: Belonocnema (Hymenoptera: Cynipidae: Cynipini) gall wasps associated with live oaks in the USA. Zool J Linn Soc 2021. [DOI: 10.1093/zoolinnean/zlab001] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Abstract
Gall wasps (Hymenoptera: Cynipidae) in the genus Belonocnema induce galls on live oaks (Quercus series Virentes), forming multilocular root galls in the sexual generation and unilocular leaf galls in the asexual generation. Using morphological characters, host records, museum specimens, flight propensity and phylogenetic analysis of published cytochrome c oxidase subunit I (COI) and nuclear SNP data, we resolve the long-standing taxonomic confusion within Belonocnema and recognize three distinct species that are distributed throughout the southern and south-eastern USA: B. fossoria (rev. stat.), B. kinseyi (rev. stat.) and B. treatae, while B. quercusvirens is treated as species inquirenda. The presence of mitonuclear discordance results in the failure of a mitochondrial DNA barcode region to distinguish between B. fossoria and B. treatae, while recognizing B. kinseyi, despite the three species being clearly separated based on morphology and phylogenetic analysis of SNP data. We provide re-descriptions and an updated dichotomous key for both asexual and sexual generations of these widespread species. Finally, as Belonocnema has emerged as a model organism for ecological and evolutionary studies, we clarify the species examined in published studies to date.
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Affiliation(s)
- Y Miles Zhang
- Systematic Entomology Laboratory, USDA-ARS, c/o National Museum of Natural History, Washington, DC, USA
| | - Scott P Egan
- Department of Biosciences, Rice University, Houston, TX, USA
| | - Amanda L Driscoe
- Department of Biology, Population and Conservation Biology Program, Texas State University, San Marcos, TX, USA
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA
| | - James R Ott
- Department of Biology, Population and Conservation Biology Program, Texas State University, San Marcos, TX, USA
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3
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Zhang L, Hood GR, Roush AM, Shzu SA, Comerford MS, Ott JR, Egan SP. Asymmetric, but opposing reductions in immigrant viability and fecundity promote reproductive isolation among host-associated populations of an insect herbivore. Evolution 2020; 75:476-489. [PMID: 33330984 DOI: 10.1111/evo.14148] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 11/27/2020] [Accepted: 12/11/2020] [Indexed: 01/04/2023]
Abstract
Immigrant inviability can contribute to reproductive isolation (RI) during ecological speciation by reducing the survival of immigrants in non-native environments. However, studies that assess the fitness consequence of immigrants moving from native to non-native environments typically fail to explore the potential role of concomitant reductions in immigrant fecundity despite recent evidence suggesting its prominent role during local adaptation. Here, we evaluate the directionality and magnitude of both immigrant viability and fecundity to RI in a host-specific gall-forming wasp, Belonocnema treatae. Using reciprocal transplant experiments replicated across sites, we measure immigrant viability and fecundity by comparing differences in the incidence of gall formation (viability) and predicted the number of eggs per female (fecundity) between residents and immigrants in each of two host-plant environments. Reduced immigrant viability was found in one host environment while reduced immigrant fecundity was found in the other. Such habitat-dependent barriers resulted in asymmetric RI between populations. By surveying recent literature on local adaptation, we find that asymmetry in immigrant viability and fecundity are widespread across disparate taxa, which highlights the need to combine estimates of both common and overlooked barriers in cases of potential bi-directional gene flow to create a more comprehensive view of the evolution of RI.
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Affiliation(s)
- Linyi Zhang
- Department of BioSciences, Rice University, Houston, Texas, 77005
| | - Glen R Hood
- Department of BioSciences, Rice University, Houston, Texas, 77005.,Department of Biological Sciences, Wayne State University, Detroit, Michigan, 48202
| | - Amy M Roush
- Department of BioSciences, Rice University, Houston, Texas, 77005
| | - Shih An Shzu
- Department of BioSciences, Rice University, Houston, Texas, 77005
| | | | - James R Ott
- Population and Conservation Biology Program, Department of Biology, Texas State University, San Marcos, Texas, 78666
| | - Scott P Egan
- Department of BioSciences, Rice University, Houston, Texas, 77005
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4
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Weaver AK, Hood GR, Foster M, Egan SP. Trade-off between fecundity and survival generates stabilizing selection on gall size. Ecol Evol 2020; 10:10207-10218. [PMID: 33005376 PMCID: PMC7520187 DOI: 10.1002/ece3.6682] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Revised: 06/27/2020] [Accepted: 07/20/2020] [Indexed: 11/09/2022] Open
Abstract
Complex interactions within multitrophic communities are fundamental to the evolution of individual species that reside within them. One common outcome of species interactions are fitness trade-offs, where traits adaptive in some circumstances are maladaptive in others. Here, we identify a fitness trade-off between fecundity and survival in the cynipid wasp Callirhytis quercusbatatoides that induces multichambered galls on the stem of its host plant Quercus virginiana. We first quantified this trade-off in natural populations by documenting two relationships: a positive association between the trait gall size and fecundity, as larger galls contain more offspring, and a negative association between gall size and survival, as larger galls are attacked by birds at a higher rate. Next, we performed a field-based experimental evolution study where birds were excluded from the entire canopy of 11 large host trees for five years. As a result of the five-year release from avian predators, we observed a significant shift to larger galls per tree. Overall, our study demonstrates how two opposing forces of selection can generate stabilizing selection on a critical phenotypic trait in wild populations, and how traits can evolve rapidly in the predicted direction when conditions change.
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Affiliation(s)
| | - Glen Ray Hood
- Department of BioSciencesRice UniversityHoustonTXUSA
- Department of Biological SciencesWayne State UniversityDetroitMIUSA
| | | | - Scott P. Egan
- Department of BioSciencesRice UniversityHoustonTXUSA
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5
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Driscoe AL, Nice CC, Busbee RW, Hood GR, Egan SP, Ott JR. Host plant associations and geography interact to shape diversification in a specialist insect herbivore. Mol Ecol 2019; 28:4197-4211. [DOI: 10.1111/mec.15220] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 07/26/2019] [Accepted: 08/07/2019] [Indexed: 12/21/2022]
Affiliation(s)
- Amanda L. Driscoe
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos Texas
| | - Chris C. Nice
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos Texas
| | - Robert W. Busbee
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos Texas
| | - Glen R. Hood
- Department of Biological Sciences Wayne State University Detroit Michigan
| | - Scott P. Egan
- Department of Biosciences Rice University Houston Texas
| | - James R. Ott
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos Texas
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Hood GR, Zhang L, Hu EG, Ott JR, Egan SP. Cascading reproductive isolation: Plant phenology drives temporal isolation among populations of a host‐specific herbivore. Evolution 2019; 73:554-568. [DOI: 10.1111/evo.13683] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Revised: 01/01/2019] [Accepted: 01/07/2019] [Indexed: 12/17/2022]
Affiliation(s)
- Glen R. Hood
- Department of BiosciencesAnderson Biological LaboratoriesRice University Houston Texas 77005
- Department of Biological SciencesWayne State University Detroit Michigan 48202
| | - Linyi Zhang
- Department of BiosciencesAnderson Biological LaboratoriesRice University Houston Texas 77005
| | - Elaine G. Hu
- Department of BiosciencesAnderson Biological LaboratoriesRice University Houston Texas 77005
| | - James R. Ott
- Population and Conservation Biology ProgramDepartment of BiologyTexas State University San Marcos Texas 78666
| | - Scott P. Egan
- Department of BiosciencesAnderson Biological LaboratoriesRice University Houston Texas 77005
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Egan SP, Zhang L, Comerford M, Hood GR. Botanical parasitism of an insect by a parasitic plant. Curr Biol 2018; 28:R863-R864. [DOI: 10.1016/j.cub.2018.06.024] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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8
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Heath JJ, Abbot P, Stireman JO. Adaptive Divergence in a Defense Symbiosis Driven from the Top Down. Am Nat 2018; 192:E21-E36. [PMID: 29897808 DOI: 10.1086/697446] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Most studies of adaptive radiation in animals focus on resource competition as the primary driver of trait divergence. The roles of other ecological interactions in shaping divergent phenotypes during such radiations have received less attention. We evaluate natural enemies as primary agents of diversifying selection on the phenotypes of an actively diverging lineage of gall midges on tall goldenrod. In this system, the gall of the midge consists of a biotrophic fungal symbiont that develops on host-plant leaves and forms distinctly variable protective carapaces over midge larvae. Through field studies, we show that fungal gall morphology, which is induced by midges (i.e., it is an extended phenotype), is under directional and diversifying selection by parasitoid enemies. Overall, natural enemies disruptively select for either small or large galls, mainly along the axis of gall thickness. These results imply that predators are driving the evolution of phenotypic diversity in symbiotic defense traits in this system and that divergence in defensive morphology may provide ecological opportunities that help to fuel the adaptive radiation of this genus of midges on goldenrods. This enemy-driven phenotypic divergence in a diversifying lineage illustrates the potential importance of consumer-resource and symbiotic species interactions in adaptive radiation.
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Weinersmith KL, Liu SM, Forbes AA, Egan SP. Tales from the crypt: a parasitoid manipulates the behaviour of its parasite host. Proc Biol Sci 2018; 284:rspb.2016.2365. [PMID: 28123089 PMCID: PMC5310038 DOI: 10.1098/rspb.2016.2365] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 01/03/2017] [Indexed: 11/26/2022] Open
Abstract
There are many examples of apparent manipulation of host phenotype by parasites, yet few examples of hypermanipulation—where a phenotype-manipulating parasite is itself manipulated by a parasite. Moreover, few studies confirm manipulation is occurring by quantifying whether the host's changed phenotype increases parasite fitness. Here we describe a novel case of hypermanipulation, in which the crypt gall wasp Bassettia pallida (a phenotypic manipulator of its tree host) is manipulated by the parasitoid crypt-keeper wasp Euderus set, and show that the host's changed behaviour increases parasitoid fitness. Bassettia pallida parasitizes sand live oaks and induces the formation of a ‘crypt’ within developing stems. When parasitized by E. set, B. pallida adults excavate an emergence hole in the crypt wall, plug the hole with their head and die. We show experimentally that this phenomenon benefits E. set, as E. set that need to excavate an emergence hole themselves are about three times more likely to die trapped in the crypt. In addition, we discuss museum and field data to explore the distribution of the crypt-keeping phenomena.
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Affiliation(s)
- Kelly L Weinersmith
- Department of BioSciences, Rice University, MS-140, 6100 Main Street, Houston, TX 77005, USA
| | - Sean M Liu
- Department of BioSciences, Rice University, MS-140, 6100 Main Street, Houston, TX 77005, USA
| | - Andrew A Forbes
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA
| | - Scott P Egan
- Department of BioSciences, Rice University, MS-140, 6100 Main Street, Houston, TX 77005, USA
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Uncovering the genetic signature of quantitative trait evolution with replicated time series data. Heredity (Edinb) 2016; 118:42-51. [PMID: 27848948 DOI: 10.1038/hdy.2016.98] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Revised: 08/18/2016] [Accepted: 08/24/2016] [Indexed: 01/04/2023] Open
Abstract
The genetic architecture of adaptation in natural populations has not yet been resolved: it is not clear to what extent the spread of beneficial mutations (selective sweeps) or the response of many quantitative trait loci drive adaptation to environmental changes. Although much attention has been given to the genomic footprint of selective sweeps, the importance of selection on quantitative traits is still not well studied, as the associated genomic signature is extremely difficult to detect. We propose 'Evolve and Resequence' as a promising tool, to study polygenic adaptation of quantitative traits in evolving populations. Simulating replicated time series data we show that adaptation to a new intermediate trait optimum has three characteristic phases that are reflected on the genomic level: (1) directional frequency changes towards the new trait optimum, (2) plateauing of allele frequencies when the new trait optimum has been reached and (3) subsequent divergence between replicated trajectories ultimately leading to the loss or fixation of alleles while the trait value does not change. We explore these 3 phase characteristics for relevant population genetic parameters to provide expectations for various experimental evolution designs. Remarkably, over a broad range of parameters the trajectories of selected alleles display a pattern across replicates, which differs both from neutrality and directional selection. We conclude that replicated time series data from experimental evolution studies provide a promising framework to study polygenic adaptation from whole-genome population genetics data.
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11
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Reynolds RJ, de los Campos G, Egan SP, Ott JR. Modelling heterogeneity among fitness functions using random regression. Methods Ecol Evol 2016; 7:70-79. [PMID: 26949509 PMCID: PMC4776641 DOI: 10.1111/2041-210x.12440] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Summary
Statistical approaches for testing hypotheses of heterogeneity in fitness functions are needed to accommodate studies of phenotypic selection with repeated sampling across study units, populations or years. In this study, we tested directly for among‐population variation in complex fitness functions and demonstrate a new approach for locating the region of the trait distribution where variation in fitness and traits is greatest.
We modelled heterogeneity in fitness functions among populations by treating regression coefficients of fitness on traits as random variates. We applied random regression using two model specifications, (i) spline‐based curve and (ii) stepwise, to a 2‐year study of selection among 16 populations of the gall wasp, Belonocnema treatae. Log‐likelihood ratio tests of variance components and 10‐fold cross‐validation were used to assess the evidence that selection varied among populations.
Ten‐fold cross‐validation prediction error sums of squares (PSS) indicated that spline‐based fitness functions were population specific and that the strength of evidence for heterogeneity in selection differed between years. Hypothesis testing of variance components from both models was consistent with the PSS results. Both the stepwise model and the local prediction error estimates of spline‐based fitness functions identified the region(s) of the phenotype distribution harbouring the greatest heterogeneity among populations.
The adopted framework advances our understanding of phenotypic selection in natural populations by extending the analysis of spline‐based fitness functions to testing for heterogeneity among study units and isolating the regions of the phenotypic distribution where this variation is most pronounced.
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Affiliation(s)
- Richard J. Reynolds
- Department of Medicine, Division of Clinical Immunology and
Rheumatology, Department of Biostatistics, University of Alabama at Birmingham,
Birmingham, Alabama 35294; (205-975-9300)
| | - Gustavo de los Campos
- Departments of Epidemiology & Biostatistics, and Statistics,
Michigan State University, East Lansing, MI, 48824, (517-353-8623)
| | - Scott P. Egan
- Department of BioSciences, Rice University, Houston, Texas 77005;
(615-618-6601)
| | - James R. Ott
- Population and Conservation Biology Program, Department of Biology,
Texas State University, San Marcos, Texas 78666, (512-245-2321)
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12
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Ott JR, Egan SP. Interspecific patterns of phenotypic selection do not predict intraspecific patterns. J Evol Biol 2013; 27:214-9. [PMID: 24164642 DOI: 10.1111/jeb.12266] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Revised: 09/13/2013] [Accepted: 09/17/2013] [Indexed: 12/01/2022]
Abstract
We estimated linear (β) and nonlinear (γ) selection gradients to quantify host plant-mediated selection on the trait gall size in each of 22 unequally sampled subpopulations of the cynipid gall wasp Belonocnema treatae. We characterized the relationship between variation in subpopulation sample size and the magnitude of and the variance among selection gradients. We then tested the hypothesis that the intraspecific patterns we observed would follow two patterns that have emerged from published estimates of linear and nonlinear selection gradients compiled across species, namely that the average magnitude of β and γ and the variance among estimated β and γ decrease with increasing sample size. For both β and γ, intraspecific patterns of phenotypic selection in relation to sample size were not predicted by interspecific patterns. Thus, our results suggest that when selection is heterogeneous among subpopulations, variation in the biological basis for selection is more important in influencing estimates of selection than is variation in study size. Our study highlights the value of inspecting selection in relation to sampling effort at the level at which understanding the sources of variation in selection is most important, among populations within species.
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Affiliation(s)
- J R Ott
- Department of Biology, Population and Conservation Biology Program, Texas State University, San Marcos, TX, USA
| | - S P Egan
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, USA.,Department of Ecology and Evolutionary Biology, Rice University, Houston, TX, USA
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13
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Synthetic analyses of phenotypic selection in natural populations: lessons, limitations and future directions. Evol Ecol 2012. [DOI: 10.1007/s10682-012-9563-5] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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