Parasites, desiderata lists and the paradox of the organism

Nonlinear social evolution and the emergence of collective action

Organisms from microbes to humans engage in a variety of social behaviors, which affect fitness in complex, often nonlinear ways. The question of how these behaviors evolve has consequences ranging from antibiotic resistance to human origins. However, evolution with nonlinear social interactions is challenging to model mathematically, especially in combination with spatial, group, and/or kin assortment. We derive a mathematical condition for natural selection with synergistic interactions among any number of individuals. This result applies to populations with arbitrary (but fixed) spatial or network structure, group subdivision, and/or mating patterns. In this condition, nonlinear fitness effects are ascribed to collectives, and weighted by a new measure of collective relatedness. For weak selection, this condition can be systematically evaluated by computing branch lengths of ancestral trees. We apply this condition to pairwise games between diploid relatives, and to dilemmas of collective help or harm among siblings and on spatial networks. Our work provides a rigorous basis for extending the notion of "actor", in the study of social evolution, from individuals to collectives.

Conflict and conflict resolution in the major transitions

Conflict and conflict resolution have been argued to be fundamental to the major transitions in evolution. These were key events in life's history in which previously independently living individuals cooperatively formed a higher-level individual, such as a multicellular organism or eusocial colony. Conflict has its central role because, to proceed stably, the evolution of individuality in each major transition required within-individual conflict to be held in check. This review revisits the role of conflict and conflict resolution in the major transitions, addressing recent work arguing for a minor role. Inclusive fitness logic suggests that differences between the kin structures of clones and sexual families support the absence of conflict at the origin of multicellularity but, by contrast, suggest that key conflicts existed at the origin of eusociality. A principal example is conflict over replacing the founding queen (queen replacement). Following the origin of each transition, conflict remained important, because within-individual conflict potentially disrupts the attainment of maximal individuality (organismality) in the system. The conclusion is that conflict remains central to understanding the major transitions, essentially because conflict arises from differences in inclusive fitness optima while conflict resolution can help the system attain a high degree of coincidence of inclusive fitness interests.

Adaptation in the face of internal conflict: the paradox of the organism revisited

The paradox of the organism refers to the observation that organisms appear to function as coherent purposeful entities, despite the potential for within-organismal components like selfish genetic elements and cancer cells to erode them from within. While it is commonly accepted that organisms may pursue fitness maximisation and can be thought to hold particular agendas, there is a growing recognition that genes and cells do so as well. This can lead to evolutionary conflicts between an organism and the parts that reside within it. Here, we revisit the paradox of the organism. We first outline its conception and relationship to debates about adaptation in evolutionary biology. Second, we review the ways selfish elements may exploit organisms, and the extent to which this threatens organismal integrity. To this end, we introduce a novel classification scheme that distinguishes between selfish elements that seek to distort transmission versus those that seek to distort phenotypic traits. Our classification scheme also highlights how some selfish elements elude a multi-level selection decomposition using the Price equation. Third, we discuss how the organism can retain its status as the primary fitness-maximising agent in the face of selfish elements. The success of selfish elements is often constrained by their strategy and further limited by a combination of fitness alignment and enforcement mechanisms controlled by the organism. Finally, we argue for the need for quantitative measures of both internal conflicts and organismality.

Genetic conflicts and the case for licensed anthropomorphizing

The use of intentional language in biology is controversial. It has been commonly applied by researchers in behavioral ecology, who have not shied away from employing agential thinking or even anthropomorphisms, but has been rarer among researchers from more mechanistic corners of the discipline, such as population genetics. One research area where these traditions come into contact—and occasionally clash—is the study of genetic conflicts, and its history offers a good window to the debate over the use of intentional language in biology. We review this debate, paying particular attention to how this interaction has played out in work on genomic imprinting and sex chromosomes. In light of this, we advocate for a synthesis of the two approaches, a form of licensed anthropomorphizing. Here, agential thinking’s creative potential and its ability to identify the fulcrum of evolutionary pressure are combined with the rigidity of formal mathematical modeling.

Experimental evolution of parasitic host manipulation

Host manipulation is a parasite-induced alteration of a host's phenotype that increases parasite fitness. However, if genetically encoded in the parasite, it should be under selection in the parasite. Such host manipulation has often been assumed to be energetically costly, which should restrict its evolution. Evidence of such costs, however, remains elusive. The trophically transmitted cestode Schistocephalus solidus manipulates the activity of its first intermediate copepod host to reduce its predation susceptibility before the parasite is ready for transmission. Thereafter, S. solidus increases host activity to facilitate transmission to its subsequent fish host. I selected S. solidus for or against host manipulation over three generations to investigate the evolvability of manipulation and identify potential trade-offs. Host manipulation responded to selection, confirming that this trait is heritable in the parasite and hence can present an extended phenotype. Changes in host manipulation were not restrained by any obvious costs.

Captive individuals of endangered Philippine raptors maintain native feather mites (Acariformes: Pterolichoidea) species

Endangered species of hosts are coupled with endangered species of parasites, which share the risk of co-extinction. Conservation efforts sometimes include breeding of rare species in captivity. Data on parasites of captive populations of endangered species is scarce and the ability of small numbers of captive host individuals to support the biodiversity of native parasites is limited. Examination of ectosymbionts of the critically endangered Philippine eagles and the endangered Mindanao Hawk-Eagle kept at the Philippine Eagle Center, Philippines, revealed three feather mite species despite regular treatment with insecticide powder. No other ectosymbiont taxa were detected. Studies in morphology and molecular phylogeny of these feather mites based on mitochondrial and nuclear DNA markers indicate that species found were typical for Accipitridae. Three new pterolichoid feather mite species (Acari: Pterolichoidea) were described from two species of eagles (Accipitriformes: Accipitridae) endemic to the Philippines: Hieracolichus philippinensis sp. n. (Gabuciniidae) and Pseudalloptinus pithecophagae sp. n. (Pterolichidae) from the Great Philippine Eagle Pithecophaga jefferyi Ogilvie-Grant, 1896, and Pseudogabucinia nisaeti sp. n. (Kramerellidae) from the Mindanao Hawk-Eagle Nisaetus pinskeri Gould, 1863. The presence of H. philippinensis on P. jefferyi supports the recent finding that the Great Philippine Eagle belongs to the lineage of serpent eagles (Circaetinae) rather than to the Harpy and other eagles.

•

Small captive groups of endangered birds can maintain native feather mite populations for decades despite regular antiparasitic treatment.

•

Our study is a first record of feather mites from endemic raptors or diurnal birds-of-prey in the Philippines, with three new species described.

•

Feather mites of the Great Philippine Eagle support the attribution of the host to the Circaetinae rather than to Harpiinae birds of prey lineages.

Opposed elevational variation in prevalence and intensity of endoparasites and their vectors in a lizard

Studying the causes of parasite geographic distribution is relevant to understand ecological and evolutionary processes that affect host populations as well as for species conservation. Temperature is one of the most important environmental variables affecting parasite distribution, as raising temperatures positively affect development, reproduction, and rate of transmission of both endo- and ectoparasites. In this context, it is generally accepted that, in mountains, parasite abundance decreases with elevation. However, empirical evidence on this topic is limited. In the present study, we analyzed the elevational variation of hemoparasites and ectoparasites of a lizard, Psammodromus algirus, along a 2,200-m elevational gradient in Sierra Nevada (SE Spain). As predicted, ectoparasite (mites, ticks, mosquitoes, and sandflies) abundance decreased with elevation. However, hemoparasite prevalence and intensity in the lizard augmented with altitude, showing a pattern contrary to their vectors (mites). We suggest that tolerance to hemoparasites may increase with elevation as a consequence of lizards at high altitudes taking advantage of increased body condition and food availability, and reduced oxidative stress. Moreover, lizards could have been selected for higher resistance against hemoparasites at lowlands (where higher rates of replication are expected), thus reducing hemoparasite prevalence and load. Our findings imply that, in a scenario of climate warming, populations of lizards at high elevation may face increased abundance of ectoparasites, accompanied with strong negative effects.

Selfish genetic elements and the gene's-eye view of evolution

During the last few decades, we have seen an explosion in the influx of details about the biology of selfish genetic elements. Ever since the early days of the field, the gene's-eye view of Richard Dawkins, George Williams, and others, has been instrumental to make sense of new empirical observations and to the generation of new hypotheses. However, the close association between selfish genetic elements and the gene's-eye view has not been without critics and several other conceptual frameworks have been suggested. In particular, proponents of multilevel selection models have used selfish genetic elements to criticize the gene's-eye view. In this paper, I first trace the intertwined histories of the study of selfish genetic elements and the gene's-eye view and then discuss how their association holds up when compared with other proposed frameworks. Next, using examples from transposable elements and the major transitions, I argue that different models highlight separate aspects of the evolution of selfish genetic elements and that the productive way forward is to maintain a plurality of perspectives. Finally, I discuss how the empirical study of selfish genetic elements has implications for other conceptual issues associated with the gene's-eye view, such as agential thinking, adaptationism, and the role of fitness maximizing models in evolution.

Venturing in coral larval chimerism: a compact functional domain with fostered genotypic diversity

The globally distributed coral species Pocillopora damicornis is known to release either sexual or asexual derived planula-larvae in various reef locations. Using microsatellite loci as markers, we documented the release of asexually derived chimeric larvae (CL), originating from mosaicked maternal colonies that were also chimeras, at Thai and Philippines reefs. The CL, each presenting different combinations of maternal genotypic constituents, create genetically-complex sets of asexual propagules. This novel mode of inheritance in corals challenges classical postulations of sexual/asexual reproduction traits, as asexual derived CL represent an alliance between genotypes that significantly sways the recruits' absolute fitness. This type of inherited chimerism, while enhancing intra-entity genetic heterogeneity, is an evolutionary tactic used to increase genetic-heterogeneity, primarily in new areas colonized by a limited number of larvae. Chimerism may also facilitate combat global change impacts by exhibiting adjustable genomic combinations of within-chimera traits that could withstand alterable environmental pressures, helping Pocillopora become a successful cosmopolitan species.

A Bacterial Parasite Effector Mediates Insect Vector Attraction in Host Plants Independently of Developmental Changes

Parasites can take over their hosts and trigger dramatic changes in host appearance and behavior that are typically interpreted as extended phenotypes that promote parasite survival and fitness. For example, Toxoplasma gondii is thought to manipulate the behaviors of infected rodents to aid transmission to cats and parasitic trematodes of the genus Ribeiroia alter limb development in their amphibian hosts to facilitate predation of the latter by birds. Plant parasites and pathogens also reprogram host development and morphology. However, whereas some parasite-induced morphological alterations may have a direct benefit to the fitness of the parasite and may therefore be adaptive, other host alterations may be side effects of parasite infections having no adaptive effects on parasite fitness. Phytoplasma parasites of plants often induce the development of leaf-like flowers (phyllody) in their host plants, and we previously found that the phytoplasma effector SAP54 generates these leaf-like flowers via the degradation of plant MADS-box transcription factors (MTFs), which regulate all major aspects of development in plants. Leafhoppers prefer to reproduce on phytoplasma-infected and SAP54-trangenic plants leading to the hypothesis that leafhopper vectors are attracted to plants with leaf-like flowers. Surprisingly, here we show that leafhopper attraction occurs independently of the presence of leaf-like flowers. First, the leafhoppers were also attracted to SAP54 transgenic plants without leaf-like flowers and to single leaves of these plants. Moreover, leafhoppers were not attracted to leaf-like flowers of MTF-mutant plants without the presence of SAP54. Thus, the primary role of SAP54 is to attract leafhopper vectors, which spread the phytoplasmas, and the generation of leaf-like flowers may be secondary or a side effect of the SAP54-mediated degradation of MTFs.

On the origins of parasite-extended phenotypes

Parasites that adaptively manipulate the behavior of their host are among the most exciting adaptations that we can find in nature. The behavior of the host can become an extended phenotype of the parasites within animals such that the success and failure of the parasite's genome rely on precise change of the host's behavior. Evolutionary biology was borne from the close attention of naturalists such as Wallace and Darwin to phenotypic variation in seeking to understand the origins of new species. In this essay, I argue that we also need to think about the origins of parasite-extended phenotypes. This is a more difficult task than understanding the evolution of textbook examples of novelty such as the eyes of vertebrates or the hooves of horses. However, new tools such as phylogenomics provide an important opportunity to make significant progress in understanding the extended phenotypes of parasites. Knowing the origins of parasite-extended phenotypes is important as a goal all by itself. But the knowledge gained will also help us understand why complex manipulation is so rare and to identify the evolutionary tipping points driving its appearance.

Immigration control in the vertebrate body with special reference to chimerism

The phenomenon of chimerism is reviewed against an understanding of adaptive immunity in vertebrates. It is shown that chimerism can be regarded as a ubiquitous condition and this suggests that monophylesis has played little part in evolution. It is suggested that the adaptive immune response has a special role in facilitating the development of chimerism and that the consensus view of adaptive immunity as a rejection mechanism should be revised.

Pathways to understanding the extended phenotype of parasites in their hosts

The study of the adaptive manipulation of animal behavior by parasites is entering very exciting times. Collectively the field has moved from its important and instructional natural history phase into proximate-level studies aiming to elucidate the mechanisms by which one organism controls another. Because many cases studies involve cross-kingdom control of behaviour, the findings are sure to be exciting. In this review I examine what possible pathways we can take to understanding the controlling behavior of parasites and how host behavior has become an extended phenotype of the parasites that is often hidden from view.

The "New World of Sciences". The temporality of the research agenda and the unending ambitions of science

Lists foreground multiplicity: both of objects to be pursued and, for distant objects, of far-flung networks enabling their pursuit. The future-oriented or projective list stretches such networks not only around the world but forward through time. Research agendas are one kind of future-oriented, projective list. Sketching how such lists have functioned over time, from Francis Bacon's "The New World of Sciences, or Desiderata" to today's desiderata lists, suggests how an early modern model of imperial expansion has shaped, in unintended ways, a scientific rhetoric of collaborative advance on shared targets.

Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection

Background

Parasites that manipulate host behavior can provide prominent examples of extended phenotypes: parasite genomes controlling host behavior. Here we focus on one of the most dramatic examples of behavioral manipulation, the death grip of ants infected by Ophiocordyceps fungi. We studied the interaction between O. unilateralis s.l. and its host ant Camponotus leonardi in a Thai rainforest, where infected ants descend from their canopy nests down to understory vegetation to bite into abaxial leaf veins before dying. Host mortality is concentrated in patches (graveyards) where ants die on sapling leaves ca. 25 cm above the soil surface where conditions for parasite development are optimal. Here we address whether the sequence of ant behaviors leading to the final death grip can also be interpreted as parasite adaptations and describe some of the morphological changes inside the heads of infected workers that mediate the expression of the death grip phenotype.

Results

We found that infected ants behave as zombies and display predictable stereotypical behaviors of random rather than directional walking, and of repeated convulsions that make them fall down and thus precludes returning to the canopy. Transitions from erratic wandering to death grips on a leaf vein were abrupt and synchronized around solar noon. We show that the mandibles of ants penetrate deeply into vein tissue and that this is accompanied by extensive atrophy of the mandibular muscles. This lock-jaw means the ant will remain attached to the leaf after death. We further present histological data to show that a high density of single celled stages of the parasite within the head capsule of dying ants are likely to be responsible for this muscular atrophy.

Conclusions

Extended phenotypes in ants induced by fungal infections are a complex example of behavioral manipulation requiring coordinated changes of host behavior and morphology. Future work should address the genetic basis of such extended phenotypes.

Behavioural fever in infected honeybees: parasitic manipulation or coincidental benefit?

Infection by a parasite often induces behavioural changes in the host and these changes may benefit either the host or the parasite. However, whether these changes are active host defence mechanisms or parasitic manipulations or simply incidental byproducts of the infection is not always clear. It has been suggested that understanding the proximate mechanisms of these changes as well as comparative studies could help distinguish these alternatives better. Behavioural fever is a common response to an infection in many animals and we investigated the phenomenon in the novel host-parasite relationship between the honeybee and the temperature-sensitive microsporidian Nosema ceranae. Our results show that infected bees prefer higher temperatures and even though this seems to benefit the pathogen, the proximate mechanism underlying this change is the pathological stress underlying the infection. Especially because it is a new host-parasite relationship, it is best to label the observed behavioural change as a case of incidental benefit although this does not rule out selection acting on it. We discuss the importance of looking at the behavioural outcomes of host-parasite relationships and the importance of studying them at multiple levels for understanding their origin and maintenance.

Effect of methanolic extract of Balanites aegyptiaca fruits on enteral and parenteral stages of Trichinella spiralis in rats

There is a considerable interest in developing new anthelmintic drugs including those from medicinal plants due to increasing evidence of parasitic resistance against present anthelmintic drugs and decreasing activity against encapsulated larval stages of parasites. This study was carried out to assess, for the first time, the effectiveness of methanolic extract of Balanites aegyptiaca (BAE) fruits against different stages (pre-adult, migrating larvae, and encysted larvae) of Trichinella spiralis in rats compared with commonly used anthelmintic albendazole. Oral administration of BAE at a dose of 1,000 mg/kg b.wt. for five successive days throughout the parasite life cycle led to a marked reduction of migrating and encysted larval rate by 81.7% and 61.7%, respectively, in the muscular tissue. This treatment was less effective against adults in the gut (47.8%). Albendazole treatment at a dose of 10 mg/kg b.wt. for five successive days resulted in a marked eradication of T. spiralis adult worms (94.4%) and less reduction of migrating and encysted larval infections of skeletal muscles (62.2% and 26.4%, respectively). BAE-treated groups showed marked decreases in serum-glucose levels, triglyceride concentrations, aspartate aminotransferase (AST), creatinine phosphokinase (CPK) activities, and lipid peroxide products (malondialdehyde, MDA) as well as an increase in glutathione level in both serum and muscular tissue compared to albendazole-treated- and infected-untreated groups. This result was confirmed by few numbers of living- and dead-encysted larvae and less destruction of the diaphragm and skeletal muscle tissues in BAE-treated groups compared to other treated groups. It can be concluded that the methanolic extract of B. aegyptiaca fruits has high effectiveness against parenteral stages of T. spiralis than albendazole. Albendazole is more effective against enteral stage of T. spiralis than the extract.

Biology of the phylum nematomorpha

Compared with most animal phyla, the Nematomorpha, also known as hair worms, is a relatively understudied metazoan phylum. Although nematomorphs make up only 1 of 3 animal phyla specializing solely on a parasitic life style, little attention has been focused on this enigmatic group scientifically. The phylum contains two main groups. The nectonematids are parasites of marine invertebrates such as hermit crabs. The gordiids are parasites of terrestrial arthropods, such as mantids, beetles, and crickets. Members of both of these groups are free-living as adults in marine and freshwaters respectively. In recent years, large strides have been made to understand this group more fully. New information has come from collection efforts, new approaches in organismal biology, modern techniques in microscopy and molecular biology. This review will focus on the advances made in four main areas of research: (1) morphology, (2) taxonomy and systematics, (3) life cycle and ecology and (4) host behavioural alterations. Recent research focus on the structure of both nectonematids and gordiids has added new insights on the morphology of adult worms and juveniles. The nervous system of gordiids is now well described, including the documentation of sensory cells. In addition, the availability of material from the juvenile of several species of gordiids has made it possible to document the development of the parasitic stage. New collections and reinvestigations of museum specimens have allowed for a critical reevaluation of the validity of established genera and species. However, traditional taxonomic work on this group continues to be hampered by two impeding factors: first is the lack of species-specific characters; and second is the problem of intraspecific variation, which has likely led to the description of numerous synonyms. Modern molecular techniques have been used recently to support independently the broad relationships among gordiids. During the turn of the millennium, the study of the life cycle and general ecology of gordiids enjoyed a revival. The pivotal outcome of this research was the domestication of a common American gordiid species, Paragordius varius. This species was the first of this phylum to be laboratory-reared. Through this research, the life cycle of several distantly related gordiid species was investigated. Other work showed that gordiids persist in the environment in the cyst stage by moving through different hosts by paratenesis. These cysts have been shown to retain infectivity for up to a year. These factors have likely contributed to the finding that gordiid cysts are one of the most common metazoans in some aquatic environments. Finally, recent work has focused on elucidating the mechanism of how gordiids make the transition from terrestrially based definitive hosts to a free-living aquatic environment. It has been shown that hosts are manipulated by the parasites to enter water. Using this study system, and using histology and proteomic tools, the method of manipulation used by these parasites is being further investigated. This manipulation, and the reaction of the cricket to this manipulation, has been postulated to benefit both the parasite and the host. Although large strides have been made within the last 10 years in the understanding of nematomorphs, we make the case that a lot of basic information remains to be uncovered. Although seemingly a daunting task, the recent advances in information and techniques lay a solid foundation for the future study of this unique group of parasites.

Evolutionary drivers of parasite-induced changes in insect life-history traits from theory to underlying mechanisms

Many hosts are able to tolerate infection by altering life-history traits that are traded-off one against another. Here the reproductive fitness of insect hosts and vectors is reviewed in the context of theories concerning evolutionary mechanisms driving such alterations. These include the concepts that changes in host reproductive fitness are by-products of infection, parasite manipulations, host adaptations, mafia-like strategies or host compensatory responses. Two models are examined in depth, a tapeworm/beetle association, Hymenolepis diminuta/Tenebrio molitor and malaria infections in anopheline mosquitoes. Parasite-induced impairment of vitellogenesis ultimately leads to a decrease in female reproductive success in both cases, though by different means. Evidence is put forwards for both a manipulator molecule of parasite origin and for host-initiated regulation. These models are backed by other examples in which mechanisms underlying fecundity reduction or fecundity compensation are explored. It is concluded that evolutionary theories must be supported by empirical evidence gained from studying molecular, biochemical and physiological mechanisms underlying changes in host life-history traits, ideally using organisms that have evolved together and that are in their natural environment.

Do three-spined sticklebacks avoid consuming copepods, the first intermediate host ofSchistocephalus solidus? — an experimental analysis of behavioural resistance

Many parasites that use intermediate hosts are transmitted to the next host through predation. If the next host's fitness is strongly reduced by the parasite, it is under selection either to recognize and avoid infected intermediate hosts or to exclude that prey species from its diet when alternative prey are available. We investigated the predator-prey interaction between laboratory bred three-spined sticklebacks (Gasterosteus aculeatus), the second intermediate host of the cestodeSchistocephalus solidus, from 2 parasitized and 1 unparasitized population, and different prey types: infected and uninfected copepods and size-matchedDaphniaas alternative prey. Copepods with infective procercoids were more active, had a lower swimming ability and were easier to catch than uninfected controls. The sticklebacks preferred moving copepods. Therefore parasitized copepods were preferentially attacked and consumed. There was no effect of the sticklebacks' parent population being parasitized or not. The sticklebacks switched fromDaphniato (uninfected) copepods in the course of a hunting sequence; this switch occurred earlier in smaller fish. With this strategy the fish maximized their feeding rate:Daphniawere easier to catch than copepods but increasingly difficult to swallow when the stomach was filling up especially for smaller fish. However, there was no indication that sticklebacks from infected populations either consumedDaphniarather than copepods or switched later in the hunting sequence to consuming copepods than fish from an uninfected population. Thus, sticklebacks did not avoid parasitized prey althoughS. solidususually has a high prevalence and causes a strong fitness reduction in its stickleback host.

Physiological and behaviour changes in common lizards parasitized by haemogregarines

The effect of haemoparasites on the physiology and behaviour traits of their hosts was examined using Haemogregarina sp., a parasite of the common lizard, Lacerta vivipara, from the south of France. Infection with haemogregarines was associated with a reduced haemoglobin concentration and an increased number of immature red blood cells. Parasitized individuals also showed a reduced oxygen consumption at rest and a lower locomotor speed. We also found that the multiplication rate of the parasite depended on the temperature at which the lizard was maintained. Between 21 and 28 °C the multiplication rate of the parasite was significantly lower than between 29 and 35 °C. This suggests that the parasites may suffer reproductive costs when hosts reduce their body temperature.

Extended phenotype: nematodes turn ants into bird-dispersed fruits

A recent study has discovered a novel extended phenotype of a nematode which alters its ant host to resemble ripe fruit. The infected ants are in turn eaten by frugivorous birds that disperse the nematode's eggs.

Coral kin aggregations exhibit mixed allogeneic reactions and enhanced fitness during early ontogeny

Background

Aggregated settlement of kin larvae in sessile marine invertebrates may result in a complex array of compatible and incompatible allogeneic responses within each assemblage. Each such aggregate can, therefore, be considered as a distinct self-organizing biological entity representing adaptations that have evolved to maximize the potential benefits of gregarious settlement. However, only sparse information exists on the selective forces and ecological consequences of allogeneic coalescence.

Results

We studied the consequences of aggregated settlement of kin larvae of Stylophora pistillata (a Red Sea stony coral), under controlled laboratory settings. When spat came into contact, they either fused, establishing a chimera, or rejected one another. A one-year study on growth and survivorship of 544 settled S. pistillata genotypes revealed six types of biological entities: (1) Single genotypes (SG); (2) Bi-chimeras (BC); (3) Bi-rejecting genotypes (BR); (4) Tri-chimera entities (TC); (5) Three-rejecting genotypes (TR); and (6) Multi-partner entities (MP; consisting of 7.5 ± 2.6 partners). Analysis of allorecognition responses revealed an array of effector mechanisms: real tissue fusions, transitory fusions and six other histoincompatible reactions (borderline formation, sutures, overgrowth, bleaching, rejection, and partner death), disclosing unalike onsets of ontogeny and complex modes of appearance within each aggregate. Evaluations at the entity level revealed that MP entities were the largest, especially in the first two months (compared with SG: 571% in the first month and 162% in the seventh month). However, at the genotype level, the SG entities were the largest and the colonies with the highest-cost-per-genotype were the TR and the MP colonies. The cost was calculated as reduced average genotype size, from 27% and 12% in the first month to 67% and 64% in the seventh month, respectively. In general, MP exhibited the highest survivorship rate (85%, after one year) and SG the lowest (54%).

Conclusion

In view of the above, we suggest that the driving force behind gregarious kin settlements in Stylophora pistillata stems from gained benefits associated with the immediate and long-term increase in total size of the MP entity, whereas survivorship rates did not draw a parallel link. Furthermore, the biological organization of MP entity exhibits, simultaneously, an intricate network of rejecting and fusible interactions in a single allogeneic intimate arena, where proposed benefits surpass costs incurred by discord among founders. Above results and documentations on gregarious settlement in other marine taxa bring us to suggest that the 'group level' of kin aggregates may serve as a ubiquitous legitimate selection entity in the evolution of a sessile mode of life in marine organisms.

Superparasitism Evolution: Adaptation or Manipulation?

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. This often yields intense competition among larvae that are sharing the same host. Why would a female oviposit in such hostile habitat instead of looking for a better quality, unparasitized host? Here we present a continuous-time model of host-parasitoid interaction and discuss alternative scenarios. This model is first used to analyze the evolution of the superparasitism behavior of a solitary proovigenic parasitoid under both time and egg limitation. Then, following the recent discovery by Varaldi et al., we allow the parasitoid to be infected by a virus that alters the superparasitism behavior of its host to enhance its own horizontal transmission. The analysis of the coevolution of this manipulative behavior with the oviposition behavior of uninfected females clarifies and quantifies the conflict that emerges between the parasitoid and its virus. The model also yields new testable predictions. For example, we expect that uninfected parasitoids should superparasite less after coevolving with the manipulative virus. More generally, this model provides a theoretical framework for analyzing the evolution of the manipulation of parasitoid life-history traits by microparasites.

Epizootiology of blood parasites in an Australian lizard: a mark-recapture study of a natural population

The dynamics of a naturally endemic blood parasite (Hepatozoon hinuliae) were studied in a lizard (Eulamprus quoyii) host population, using 2 years of longitudinal data. We investigated how parasite abundance in the population varied over time, examined whether certain host sub-populations were more prone to infection, and compared parasite loads in relation to host reproductive behaviour. We recorded blood parasite infections of 331 individuals, obtained in 593 captures. Prevalence (the proportion of the host population infected) of blood parasites was high; approximately 66% of the lizard population was infected. Probability of infection increased with host age and size, but did not differ between the sexes. Within individuals, parasite load (the intensity of infection within individuals) did not vary over time, and was independent of host reproductive behaviour. Parasite load was significantly higher in males compared to females.

Effect of the cestode macroparasite Schistocephalus pungitii on the reproductive success of ninespine stickleback, Pungitius pungitius

We quantified the relationship between reproductive status in the ninespine stickleback, Pungitius pungitius (L., 1758), and parasitism by plerocercoids of the cestode Schistocephalus pungitii Dubinina, 1959 in Airolo Lake, Alaska, using fish specimens from the 1994, 1998, and 2000 reproductive seasons. Infected females were inhibited from producing clutches of eggs and infected males showed much-reduced testicular condition. These deleterious effects on reproduction appear to involve nutrient theft. In addition, there appears to be a greater physical effect of the parasites crushing the gonads of host fish. The results of this study support the theoretical prediction that S. pungitii is a parasitic castrator, as the fitness of the majority of infected female ninespine stickleback was apparently reduced to zero, and there may be a similar effect among the majority of male ninespine stickleback. The symptoms of infection may represent adaptive parasite manipulations resulting in larger, more fecund parasites or an extended parasite-transmission period, although the possibility that the symptoms represent nonadaptive side effects cannot be excluded.

Protochordate concordant xenotransplantation settings reveal outbreaks of donor cells and divergent life span traits

If fulminate rejection in allogeneic and xenogeneic engraftments is not an evolutionary relict feature, then any treatment that ablates the host surveillance's effector arms capabilities and eliminates graft vs. host reactivity should induce donor chimerism in transplant settings. We demonstrate here marked proliferative response of Botryllus (Urochordata) blood cells months following their infusions (2x10(4)-10(5) blood cells per host) into the concordant xenogeneic environment of irradiated Botrylloides soma. The state of infused cells was followed by Botryllus specific microsatellite alleles on DNA samples from host zooids and vascular system. Increased growth rates and life spans of engrafted hosts in some cases, and sudden chimerical death following the outbreak of donor cells in others, indicate a 'double-edged sword' expression of concurrent evolutionary selected mechanisms. This DES phenomenon in immunity underlies divergent stem cell competition phenomena in multicellular organisms, leading in mammals, to cases of autoimmune diseases vis-à-vis long-lasting microchimerism events following an iatrogenic transplantation.

Biology of the schistosome genus Trichobilharzia

Trichobilharzia is the largest genus within the family Schistosomatidae, covering over 40 species of avian parasites. To clarify the existing confusion in the systematics of the genus, we recommend combining knowledge of life cycles and developmental stages, snail/bird hosts, cytogenetical and molecular data together with morphological criteria for the characterization of particular species. The high specificity of Trichobilharzia for the intermediate host is a likely reflection of the ability to avoid the internal defence of specific snails. The spectrum of final hosts (birds) seems to be much wider. The infection of birds--trichobilharziasis--may lead to considerable tissue injuries, caused by eggs of the parasite or migration of immature/mature worms through the body. Most Trichobilharzia (visceral species) migrate through the viscera of the host, but nasal species display a neurotropic mode of migration. Due to a low specificity of penetrating cercariae, mammals (including humans) can be attacked. This leads to cercarial dermatitis, predominantly in sensitized hosts. Experimental infections indicate that Trichobilharzia never mature in an incompatible (mammalian) host. However, not all cercariae and schistosomula are necessarily trapped and eliminated in the skin, and parasites may migrate throughout the viscera and the nervous system of mammals. These findings suggest that the pathogenicity of Trichobilharzia may have been underestimated in the past and health risks associated with trichobilharziasis need to be studied further.

Reduction of egg size in natural populations of threespine stickleback infected with a cestode macroparasite

Manifestations of infectious disease may represent host adaptations to avoid or reduce the effects of infection on host fitness, parasite manipulations that benefit the pathogen's fitness, or nonadaptive side effects of parasitism. Threespine stickleback fish (Gasterosteus aculeatus) from Alaska and the cestode macroparasite Schistocephalus solidus provide an excellent system for study of the effects of parasitism on host egg size because females in populations there are capable of producing clutches of eggs in the face of substantial infection, contrary to the inhibition of reproduction that has been observed in other stickleback populations or other species of fish. A side effect resulting in reduction of mean ovummass among infected females was predicted based on the egg production process in female stickleback, the considerable energy and resource demands of S. solidus, and the chronic and progressive nature of the effects the macroparasite should have on the host fish. In each of 9 populations of G. aculeatus representing replicate natural experiments in lakes scattered across the Matanuska-Susitna Valley and the Kenai Peninsula of south-central Alaska and among all populations combined, the mean ovum mass of infected female fish is significantly reduced in comparison with that of uninfected females taken from the same population at the same time. Reduction in mean female egg mass ranged from 8 to 32% across all populations. To examine whether reduction in mean female ovum mass was a nonadaptive side effect or an adaptation, relatively large data sets from 2 of the populations were used. Mean ovum mass of infected females was predicted to decrease directly in relation to parasite index (PI) if the diminution in mean egg mass were the result of a nonadaptive side effect resulting from host nutrient loss. Alternatively, the absence of a relationship between PI and reduction in ovum mass is predicted if decreases in mean female ovum mass result from host or parasite adaptation (or both) because lightly infected hosts should show a response similar to that of heavily infected ones. In each of the 2 populations, there is a significant, negative relationship between mean female ovum mass and PI, demonstrating a correlation between the decrease in ovum mass and the level of infection. Thus, the results are consistent with the hypothesis that the reductions in mean female egg mass represent side effects of parasitism involving nutrient theft. Moreover, the proportional decline in egg mass with increasing PI apparently differed between the 2 populations, and there was no significant relationship between mean percent decrease in mean female ovum mass and mean PI across populations. These observations suggest that unknown ecological and evolutionary factors influence the degree of reduction in mean ovum mass in a population-specific manner.

The colonial urochordate Botryllus schlosseri: from stem cells and natural tissue transplantation to issues in evolutionary ecology

The urochordates, whose stem groups may have included the direct predecessors of the chordate line, serve as an excellent model group of organisms for a variety of scientific disciplines. One taxon, the botryllid ascidian, has emerged as the model system for studying allorecognition; this work has concentrated on the cosmopolitan species Botryllus schlosseri. Studies analyzing self-nonself recognition in this colonial marine organism point to three levels of allorecognition, each associated with different outcomes. The first level controls natural allogeneic rejections and fusions, in which blood-shared chimeras are formed. The second level leads to morphological resorption of partners within chimeras while the third allows the development of somatic and germ cell parasitic events. Recent studies on multi-chimeric entities formed in allogeneic fusions reveal evolutionary links between allorecognition, stem cell biology and ecology. Thus, the Botryllus system generates perspectives from different biological disciplines to yield a unique life history portrait.

Phenotypic modification of roach (Rutilus rutilus L.) infected with Ligula intestinalis L. (Cestoda: Pseudophyllidea)

In European freshwater, cyprinid fish may be heavily infected by plerocercoids of the pseudophyllidea cestode Ligula intestinalis (L.). During their development, these parasites grow rapidly to a large size in the fish's body cavity, characteristically distending the abdomen. In this study, the influence of this tapeworm on roach (Rutilus rutilus L.) morphology was analyzed. Forty-five infected and 45 uninfected roach were collected from the Lavernose-Lacasse gravel pit in Toulouse, south western France and examined for 40 morphological measurements to study phenotypic modification of the body and 14 bilateral characters for an analysis of asymmetry. Results indicate that the degree of bilateral asymmetry does not change between infected and uninfected roach, despite the strong host-morphological modifications such as deformation of the abdomen, fin displacements at the level of the tail, and sagging of the vertebral column. The intensity of abdominal distension and fish morphology changes depends on the total parasite biomass present. Differences were observed in morphology at different levels of infection, which relate to established effects of L. intestinalis on the physiology and behavior of intermediate hosts. These morphological changes induced by the parasite could increase trophic transmission to the definitive avian hosts.

A parasite that increases host lifespan

Tenebrio molitor is an intermediate host for the rat tapeworm, Hymenolepis diminuta. Parasite oncospheres hatch in the beetle midgut and burrow through into the haemocoel, where they rapidly grow and mature into metacestodes. Repair of damage incurred during invasion and the nutritional demands of the parasites are likely to impose costs on the host. Despite these costs, there is an overall very highly significant difference in survival time (p < 0.001) between infected and control populations of beetles, with a hazard ratio of 2.35 (control versus infected). Infected females showed a 40% increase in survival time to 50% mortality and males showed a 25% increase in survival time to 50% mortality. This parasite-induced increase in host longevity is discussed in the light of changes in resource allocation that may occur in infected beetles. Previous findings have demonstrated that reproductive success is significantly reduced in infected females. The outcome of changes in the reproductive effort made by male beetles is less clear. We suggest that the optimum trade-off between reproduction and longevity may be altered to favour longer host survivorship, which is likely to enhance parasite transmission.

Diallyl sulfide--a flavour component from garlic (Allium sativum) attenuates lipid peroxidation in mice infected with Trichinella spiralis

We investigated the antioxidant capacity of diallyl sulfide (DAS) in the course of experimental trichinellosis in C3H mice. For this purpose, the mice were orally infected with either Trichinella spiralis larvae (300 larvae/mouse) or treated per os with normal saline (control), and 12 hrs later, they were treated per os with DAS (200 mg/kg b.w) daily for 5 or 20 days. On day 5 and 35 of the post-infection period (5 and 35 dpi), thiobarbituric-acid reactive substances (TBARS) in the small intestinal mucosa and diaphragm samples and the total antioxidant status (TAS) of blood were determined. Trichinella spiralis increased TBARS and decreased TAS in the intestinal phase of invasion. However, in the muscular phase mice, neither TBARS nor TAS was found to be different from those of the control. Diallyl sulfide has been shown to decrease TBARS and the agent did not have any effect(s) on the total antioxidant status of blood in Trichinella-infected mice. The results suggest that diallyl sulfide may be an effective antioxidant candidate and may therefore play a significant role in the defense against lipid peroxidation in trichinellosis.

Parasite manipulation of insect reproduction: who benefits?

Host fertility is often curtailed as a result of parasitic infection. The hypothesis that this may confer an adaptive advantage upon the symbionts if nutrients are directed from reproduction and made available for host/parasite maintenance is explored. The suggestion is made that an understanding of the mechanisms underlying the pathophysiology of fecundity reduction may shed light upon the evolutionary implications of this strategy for both parasite and host. To illustrate this the down-regulation of egg production is explored with reference to a particular model system, the association between metacestodes of the rat tapeworm, Hymenolepis diminuta and the mealworm beetle, Tenebrio molitor. Several aspects of host reproductive behavior and physiology are affected by infection in this association, including vitellogenesis. Metacestodes directly inhibit the fat body synthesis of vitellogenin in a stage-specific, density-dependent manner. This inhibition is likely to be orchestrated by a modulator molecule, produced by the parasite. In the ovarian follicles, juvenile hormone III binding to a specific follicular membrane-binding protein is inhibited in infected beetles, resulting in the down-regulation of a cascade of events which enables vitellogenin to pass into the developing oocyte. Data to support the proposed existence of a parasite-induced antigonadotrophin, of host origin, are discussed. Evidence that similar mechanisms operate in Plasmodium-infected anopheline mosquitoes and Onchocerca-infected blackflies is presented in support of the possibility that a parasite-induced reduction in host reproductive fitness is an adaptive strategy and an assessment of who is manipulating whom is made.

The effect of the mermithid parasite Gasteromermis sp. (Nematoda: Mermithidae) on the drift behaviour of its mayfly host, Baetis bicaudatus (Ephemeroptera: Baetidae): a trade-off between avoiding predators and locating food

This study reports alterations in the drift behaviour of mayfly nymphs (Baetis bicaudatus) infected with the mermithid nematode parasite Gasteromermis sp. with respect to (i) their exposure to drift-feeding trout predators and (ii) the efficiency with which they locate food. Experimental stream channels and benthic and drift samples were combined to investigate drift behaviour. The drift behaviour of earlier instars did not differ between parasitized and unparasitized nymphs. Infected late-instar nymphs, however, drifted less frequently, drifted higher in the water column, and swam more frequently while drifting. Neither drift distances nor body angle while drifting were altered. Parasitized nymphs showed a reduction in food-location success in heterogeneous stream channels. The drift alterations therefore reduce both the exposure of the host to fish predators and the efficiency with which it locates food. The mayfly population is effectively divided into two groups: unparasitized nymphs (in which drift behaviour is of consequence to mayfly fecundity) and parasitized nymphs (in which drift behaviour is of consequence to mermithid survival and fecundity). It is suggested that locating food may be less important to the parasite, while the risk of trout predation may be higher for drifting parasitized individuals. Both of these factors would favour the parasite influencing its host to adopt lower drift frequencies.

The effects of deworming on indicators of school performance in Guatemala

Intestinal helminths are among the most common infections in school-age children. Of 246 children, aged 7-12 years, attending school in rural Guatemala, 91% carried Ascaris lumbricoides and 82% carried Trichuris trichiura. These children were randomly assigned to receive either albendazole or placebo at 0 and 12 weeks in a 'double-blind' study of the effects of deworming on indicators of school performance. Albendazole successfully rid the children of Ascaris but it was less effective against Trichuris. The children's performance in tests of reading and vocabulary were measured at 0 and 24 weeks, the Peabody picture vocabulary test was given at 24 weeks, and attendance was measured throughout the school year. Comparison of the treated and placebo groups showed no positive effect of deworming. The treated children were largely free of Ascaris for at least 6 months, but during that period we could not detect any improvement in reading, vocabulary, or attendance. The effects of being Trichuris-free were not examined because of the limited effectiveness of albendazole against this worm at the dosage used.