Biochemical and histological changes in the brain of the cricket Nemobius sylvestris infected by the manipulative parasite Paragordius tricuspidatus (Nematomorpha)

Recent advances in insect thermoregulation

Ambient temperature (Ta) is a critical abiotic factor for insects that cannot maintain a constant body temperature (Tb). Interestingly, Ta varies during the day, between seasons and habitats; insects must constantly cope with these variations to avoid reaching the deleterious effects of thermal stress. To minimize these risks, insects have evolved a set of physiological and behavioral thermoregulatory processes as well as molecular responses that allow them to survive and perform under various thermal conditions. These strategies range from actively seeking an adequate environment, to cooling down through the evaporation of body fluids and synthesizing heat shock proteins to prevent damage at the cellular level after heat exposure. In contrast, endothermy may allow an insect to fight parasitic infections, fly within a large range of Ta and facilitate nest defense. Since May (1979), Casey (1988) and Heinrich (1993) reviewed the literature on insect thermoregulation, hundreds of scientific articles have been published on the subject and new insights in several insect groups have emerged. In particular, technical advancements have provided a better understanding of the mechanisms underlying thermoregulatory processes. This present Review aims to provide an overview of these findings with a focus on various insect groups, including blood-feeding arthropods, as well as to explore the impact of thermoregulation and heat exposure on insect immunity and pathogen development. Finally, it provides insights into current knowledge gaps in the field and discusses insect thermoregulation in the context of climate change.

Infection patterns and new definitive host records for New Zealand gordiid hairworms (phylum Nematomorpha)

Some parasites modify the phenotype of their host in order to increase transmission to another host or to an environment suitable for reproduction. This phenomenon, known as host manipulation, is found across many parasite taxa. Freshwater hairworms are known for the behavioural changes they cause in their terrestrial arthropod hosts, increasing their likelihood of entering water to exit the host and reproduce. Understanding how infected arthropods move around in the natural environment could help uncover alterations in spatial distribution or movement induced by hairworms in their terrestrial definitive hosts. Moreover, few hairworm-host records exist for New Zealand, so any additional record could help elucidate their true host specificity. Here, we investigated whether infected terrestrial arthropods were more likely to approach streams in two subalpine communities of invertebrates, using a spatial grid of specialised pitfall traps. Although hairworm infection could not explain the movements of arthropod hosts near streams, we found several new host records for hairworms, including the first records for the recently described Gordionus maori. We also found some new host-parasite associations for mermithid nematodes. These records show that the host specificity of hairworms is quite low, suggesting that their diversity and distribution may be greater than what is currently known for New Zealand.

Caste, Sex, and Parasitism Influence Brain Plasticity in a Social Wasp

Brain plasticity is widespread in nature, as it enables adaptive responses to sensory demands associated with novel stimuli, environmental changes and social conditions. Social Hymenoptera are particularly well-suited to study neuroplasticity, because the division of labor amongst females and the different life histories of males and females are associated with specific sensory needs. Here, we take advantage of the social wasp Polistes dominula to explore if brain plasticity is influenced by caste and sex, and the exploitation by the strepsipteran parasite Xenos vesparum. Within sexes, male wasps had proportionally larger optic lobes, while females had larger antennal lobes, which is consistent with the sensory needs of sex-specific life histories. Within castes, reproductive females had larger mushroom body calyces, as predicted by their sensory needs for extensive within-colony interactions and winter aggregations, than workers who frequently forage for nest material and prey. Parasites had different effects on female and male hosts. Contrary to our predictions, female workers were castrated and behaviorally manipulated by female or male parasites, but only showed moderate differences in brain tissue allocation compared to non-parasitized workers. Parasitized males maintained their reproductive apparatus and sexual behavior. However, they had smaller brains and larger sensory brain regions than non-parasitized males. Our findings confirm that caste and sex mediate brain plasticity in P. dominula, and that parasitic manipulation drives differential allocation of brain regions depending on host sex.

NEW DEFINITIVE HOST RECORD FOR CHORDODES MORGANI (NEMATOMORPHA) IN NEBRASKA WITH NOTES ON ECOLOGY

The life cycle and ecology of the horsehair worm Chordodes morgani (Nematomorpha) in Nebraska remain unknown. To identify its definitive host, we installed a series of pitfall traps along 3 first-order streams at 4 sites: Elk Creek, Upper Elk Creek, Maple Creek, and West Oak Creek, all located northwest of Lincoln, Nebraska. In addition, we opportunistically hand-collected insects at these sites, including wood cockroaches (Parcoblatta virginica), and maintained them in the lab until they passed adult worms. Two of these field-collected wood cockroaches each yielded 1 adult worm, which was identified as C. morgani by microscopy, showing that P. virginica serves as a definitive host. Experimental infections of captive-reared Parcoblatta americana supported this result. The wood cockroach was found at all 3 creeks, but C. morgani was not found at West Oak Creek, suggesting that the definitive host does not limit the distribution of C. morgani. Physical properties of the streams were measured to examine how these properties influenced the distribution of the worm. Flow rate and pH differed between the 3 sites where C. morgani was found and the West Oak Creek site, suggesting an important role for these abiotic factors in the distribution of this horsehair worm species.

When fiction becomes fact: exaggerating host manipulation by parasites

In an era where some find fake news around every corner, the use of sensationalism has inevitably found its way into the scientific literature. This is especially the case for host manipulation by parasites, a phenomenon in which a parasite causes remarkable change in the appearance or behaviour of its host. This concept, which has deservedly garnered popular interest throughout the world in recent years, is nearly 50 years old. In the past two decades, the use of scientific metaphors, including anthropomorphisms and science fiction, to describe host manipulation has become more and more prevalent. It is possible that the repeated use of such catchy, yet misleading words in both the popular media and the scientific literature could unintentionally hamper our understanding of the complexity and extent of host manipulation, ultimately shaping its narrative in part or in full. In this commentary, the impacts of exaggerating host manipulation are brought to light by examining trends in the use of embellishing words. By looking at key examples of exaggerated claims from widely reported host-parasite systems found in the recent scientific literature, it would appear that some of the fiction surrounding host manipulation has since become fact.

Parasite-altered feeding behavior in insects: integrating functional and mechanistic research frontiers

Research on parasite-altered feeding behavior in insects is contributing to an emerging literature that considers possible adaptive consequences of altered feeding behavior for the host or the parasite. Several recent ecoimmunological studies show that insects can adaptively alter their foraging behavior in response to parasitism. Another body of recent work shows that infection by parasites can change the behavior of insect hosts to benefit the parasite; manipulations of host feeding behavior may be part of this phenomenon. Here, we address both the functional and the underlying physiological frontiers of parasite-altered feeding behavior in order to spur research that better integrates the two. Functional categories of parasite-altered behavior that are adaptive for the host include prophylaxis, therapy and compensation, while host manipulation is adaptive for the parasite. To better understand and distinguish prophylaxis, therapy and compensation, further study of physiological feedbacks affecting host sensory systems is especially needed. For host manipulation in particular, research on mechanisms by which parasites control host feedbacks will be important to integrate with functional approaches. We see this integration as critical to advancing the field of parasite-altered feeding behavior, which may be common in insects and consequential for human and environmental health.

Host manipulation by cancer cells: Expectations, facts, and therapeutic implications

Similar to parasites, cancer cells depend on their hosts for sustenance, proliferation and reproduction, exploiting the hosts for energy and resources, and thereby impairing their health and fitness. Because of this lifestyle similarity, it is predicted that cancer cells could, like numerous parasitic organisms, evolve the capacity to manipulate the phenotype of their hosts to increase their own fitness. We claim that the extent of this phenomenon and its therapeutic implications are, however, underappreciated. Here, we review and discuss what can be regarded as cases of host manipulation in the context of cancer development and progression. We elaborate on how acknowledging the applicability of these principles can offer novel therapeutic and preventive strategies. The manipulation of host phenotype by cancer cells is one more reason to adopt a Darwinian approach in cancer research.

Parasite-related modification of mating behaviour and refuge use in the aquatic isopod Caecidotea intermedius: neurological correlates

The acanthocephalan Acanthocephalus dirus is a trophically transmitted parasite that infects freshwater isopods as intermediate hosts and fish as definitive hosts. Using a laboratory-based experiment, we examined if parasite infection was associated with changes in mating behaviour, refuge use and neurochemical levels of infected isopods (Caecidotea intermedius). Infected isopods were less likely to engage in mating behaviour and more likely to be located in the open than uninfected isopods. Infected isopods also contained lower levels of serotonin (5-HT) and dopamine (DA) and had a greater mass of neural tissue (CNS) than uninfected isopods. We propose that the parasite-related changes in mating behaviour and refuge use may be modulated by the serotonergic and dopaminergic systems. We also suggest that the parasites could potentially be modulating these behavioural changes by exploiting the neural-immune system of the hosts through their neuroinflammatory responses.

Intra-cellular bacterial infections affect learning and memory capacities of an invertebrate

Background

How host manipulation by parasites evolves is fascinating but challenging evolutionary question remains. Many parasites share the capacity to manipulate host behavior increasing their transmission success. However, little is known about the learning and memory impact of parasites on their host. Wolbachia are widespread endosymbionts and infect most insect species. These bacteria are maternally transmitted and mainly alter the reproduction of hosts with weak virulence. We tested the impact of parasites (Wolbachia) on their host learning and memory capacities. To address this question we trained individuals to one direction with positive reinforcement. We compared performances between individual Wolbachia-free, Wolbachia naturally and Wolbachia artificially infected individuals.

Results

We report that in the host parasite interaction (Armadillidium vulgare/Wolbachia) naturally infected individuals Wolbachia or transinfected adult with Wolbachia are less likely to learn and memorize the correct direction with social reinforcement compared to Wolbachia-free individuals.

Conclusions

Our results imply that Wolbachia impact in the central nervous system of their host altering the memory formation and maintenance. We conclude that host manipulation can affect cognitive processes decreasing host adaptation capacities.

Calling Behavior of Male Acheta domesticus Crickets Infected with Paragordius varius (Nematomorpha: Gordiida)

It is well established that parasites in the phylum Nematomorpha induce suicide behavior of their insect hosts to bring adult worms to the appropriate habitat for emergence. It is not well established, however, whether other nematomorph-induced behavioral alterations occur before worm emergence. The purpose of our study was to evaluate the effect of the nematomorph Paragordius varius on the calling behavior of the male house cricket Acheta domesticus . We hypothesized that cricket calling, an energetically expensive and risky behavior, would be a potential target for nematomorph-induced behavioral alterations. We assessed if and how infection with P. varius affects A. domesticus calling behavior and whether the presence of wings at time of exposure to P. varius influenced changes in calling behavior. We recorded the calling behavior of male A. domesticus over the course of their infection after exposure to P. various before or after wing development. Additionally, we assessed whether winged crickets were "callers" or "noncallers" before exposure. We found that regardless of cricket developmental stage (or age) at time of infection, infected crickets spent significantly less time calling than their uninfected counterparts but only during the later stages of infection. Developmental stage at infection did affect whether crickets became callers: when infected before wing development significantly more uninfected crickets initiated calling; there was no difference between infected and uninfected crickets when infected as winged adults. Infection was a factor in whether callers stopped calling, with more infected crickets ceasing to call than uninfected crickets. This is the first study to show that infection with nematomorphs affects calling behavior of their insect host. Cricket calling behavior is immensely complex and although it was difficult to elucidate the adaptive nature of these parasite-induced behavioral changes, this study lays the groundwork for future studies to begin teasing out the factors that will help make the determination between side effect of infection or parasite/host adaptation.

Behavioral and memory changes in Mus musculus coinfected by Toxocara canis and Toxoplasma gondii

Several researchers have stated that parasites can alter the behavior of their hosts, in order to increase the transmission rate, principally when prey-predator relationships are a reliable way of infection transmission. The aim of this study was to verify the occurrence of changes in anxiety and short-term memory patterns in experimentally infected Mus musculus by Toxocara canis and/or Toxoplasma gondii. Forty male Mus musculus (Balb/c) eight-week-old were divided into four groups of 10 mice each. One group was infected with 300 eggs of Toxocara canis; a second group was submitted to infection with 10 cysts of Toxoplasma gondii; a third group was concomitantly infected with both parasites with the same inoculums and the last group was maintained without infection. The anxiety levels were evaluated using an elevated plus maze and an actometer; the short-term memory was determined by a two-way active avoidance equipment. The determination of anxiety levels were conducted 40 and 70 days after infection and the short-term memory was evaluated 140 days after infection. Mice chronically infected by Toxoplasma gondii showed impaired learning and short-term memory, but no significant differences were found in mice infected by Toxocara canis or concomitantly infected by Toxocara canis and Toxoplasma gondii when compared to non infected mice.

Ecological genomics of host behavior manipulation by parasites

Among the vast array of niche exploitation strategies exhibited by millions of different species on Earth, parasitic lifestyles are characterized by extremely successful evolutionary outcomes. Some parasites even seem to have the ability to 'control' their host's behavior to fulfill their own vital needs. Research efforts in the past decades have focused on surveying the phylogenetic diversity and ecological nature of these host-parasite interactions, and trying to understand their evolutionary significance. However, to understand the proximal and ultimate causes of these behavioral alterations triggered by parasitic infections, the underlying molecular mechanisms governing them must be uncovered. Studies using ecological genomics approaches have identified key candidate molecules involved in host-parasite molecular cross-talk, but also molecules not expected to alter behavior. These studies have shown the importance of following up with functional analyses, using a comparative approach and including a time-series analysis. High-throughput methods surveying different levels of biological information, such as the transcriptome and the epigenome, suggest that specific biologically-relevant processes are affected by infection, that sex-specific effects at the level of behavior are recapitulated at the level of transcription, and that epigenetic control represents a key factor in managing life cycle stages of the parasite through temporal regulation of gene expression. Post-translational processes, such as protein-protein interactions (interactome) and post translational modifications (e.g. protein phosphorylation, phosphorylome), and processes modifying gene expression and translation, such as interactions with microRNAs (microRNAome), are examples of promising avenues to explore to obtain crucial insights into the proximal and ultimate causes of these fascinating and complex inter-specific interactions.

Investigating candidate neuromodulatory systems underlying parasitic manipulation: concepts, limitations and prospects

Studies addressing the functional basis of parasitic manipulation suggest that alteration of the neuromodulatory system is a common feature of manipulated hosts. Screening of the neuromodulatory system has so far been carried out by performing ethopharmacological analysis, biochemical quantification of neurotransmitters and neuromodulators, and/or immunocytochemistry. Here, we review the advantages and limitations of such approaches through the analysis of case studies. We further address whether the analysis of candidate neuromodulatory systems fits the current view of manipulation as being multidimensional. The benefits in combining ethopharmacology with more recent molecular tools to investigate candidate neuromodulatory pathways is also emphasized. We conclude by discussing the value of a multidisciplinary study of parasitic manipulation, combining evolutionary (parasite transmission), behavioural (syndrome of manipulation) and neuroimmunological approaches.

Survival of larval and cyst stages of gordiids (Nematomorpha) after exposure to freezing

Hairworms infect terrestrial arthropods and are 1 of the most understudied groups of parasites. Recently, life cycles of 2 gordiids (Paragordius varius and Paragordius obamai) have been domesticated in the laboratory. We tested the viability of laboratory reared and post-frozen larval and cyst stages of the North American gordiid, P. varius , frozen at -80 C for 7 mo, and the viability of field collected and post-frozen cysts of the African (P. obamai) and North American ( P. varius ) gordiid frozen at -20 C for 2 mo. All snails exposed to post-frozen or control P. varius larvae became infected with cysts, and there was no significant difference in prevalence or mean intensity of cysts among control or experimental snail groups. As with larvae, no significant differences were observed in prevalence or mean intensity of emerging worms from crickets infected with post-frozen or control P. obamai or P. varius cysts. All female P. obamai and P. varius worms from control and post-frozen cyst infections laid eggs and larvae hatched from some of these eggs. Survival and cyst formation of P. varius larvae exposed to different combinations of drying and/or freezing temperatures indicated that gordiid larvae have the ability to survive drying and freezing, but survival significantly increases during freezing at lower temperatures. The major contribution of our study is the demonstration that gordiid larval and cyst stages can survive freezing temperatures to infect and develop in the next host.

Water-seeking behavior in worm-infected crickets and reversibility of parasitic manipulation

One of the most fascinating examples of parasite-induced host manipulation is that of hairworms, first, because they induce a spectacular "suicide" water-seeking behavior in their terrestrial insect hosts and, second, because the emergence of the parasite is not lethal per se for the host that can live several months following parasite release. The mechanisms hairworms use to increase the encounter rate between their host and water remain, however, poorly understood. Considering the selective landscape in which nematomorph manipulation has evolved as well as previously obtained proteomics data, we predicted that crickets harboring mature hairworms would display a modified behavioral response to light. Since following parasite emergence in water, the cricket host and parasitic worm do not interact physiologically anymore, we also predicted that the host would recover from the modified behaviors. We examined the effect of hairworm infection on different behavioral responses of the host when stimulated by light to record responses from uninfected, infected, and ex-infected crickets. We showed that hairworm infection fundamentally modifies cricket behavior by inducing directed responses to light, a condition from which they mostly recover once the parasite is released. This study supports the idea that host manipulation by parasites is subtle, complex, and multidimensional.

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.

Parasite manipulation of brain monoamines in California killifish (Fundulus parvipinnis) by the trematode Euhaplorchis californiensis

California killifish (Fundulus parvipinnis) infected with the brain-encysting trematode Euhaplorchis californiensis display conspicuous swimming behaviours rendering them more susceptible to predation by avian final hosts. Heavily infected killifish grow and reproduce normally, despite having thousands of cysts inside their braincases. This suggests that E. californiensis affects only specific locomotory behaviours. We hypothesised that changes in the serotonin and dopamine metabolism, essential for controlling locomotion and arousal may underlie this behaviour modification. We employed micropunch dissection and HPLC to analyse monoamine and monoamine metabolite concentrations in the brain regions of uninfected and experimentally infected fish. The parasites exerted density-dependent changes in monoaminergic activity distinct from those exhibited by fish subjected to stress. Specifically, E. californiensis inhibited a normally occurring, stress-induced elevation of serotonergic metabolism in the raphae nuclei. This effect was particularly evident in the experimentally infected fish, whose low-density infections were concentrated on the brainstem. Furthermore, high E. californiensis density was associated with increased dopaminergic activity in the hypothalamus and decreased serotonergic activity in the hippocampus. In conclusion, the altered monoaminergic metabolism may explain behavioural differences leading to increased predation of the infected killifish by their final host predators.

Manipulative parasites in the world of veterinary science: implications for epidemiology and pathology

One of the most complex and least understood transmission strategies displayed by pathogenic parasites is that of manipulation of host behaviour. A wide variety of parasites alter their host's behaviour, including species of medical and veterinary importance, such as Diplostomum spathaceum, Echinococcus spp. and Toxoplasma gondii. The manipulative ability of these parasites has implications for pathology and transmission dynamics. Domestic animals are hosts for manipulative pathogens, either by being the target host and acquiring the parasite as a result of vector-host manipulation, or by having their behaviour changed by manipulative parasites. This review uses several well-known pathogens to demonstrate how host manipulation by parasites is potentially important in epidemiology.

Manipulation of host behavior by parasitic insects and insect parasites

Parasites often alter the behavior of their hosts in ways that are ultimately beneficial to the parasite or its offspring. Although the alteration of host behavior by parasites is a widespread phenomenon, the underlying neuronal mechanisms are only beginning to be understood. Here, we focus on recent advances in the study of behavioral manipulation via modulation of the host central nervous system. We elaborate on a few case studies, in which recently published data provide explanations for the neuronal basis of parasite-induced alteration of host behavior. Among these, we describe how a worm may influence the nervous system of its cricket host and manipulate the cricket into committing suicide by jumping into water. We then focus on Ampulex compressa, which uses an Alien-like strategy for the sake of its offspring. Unlike most venomous hunters, this wasp injects venom directly into specific cerebral regions of its cockroach prey. As a result of the sting, the cockroach remains alive but immobile, but not paralyzed, and serves to nourish the developing wasp larva.

An anomaly against a current paradigm--extremely low rates of individual fecundity variability of the Gordian worm (Nematomorpha: Gordiida)

SUMMARY

Extreme variation in reproductive success (VRS) has been reported as a common feature of populations. Few individuals producing most of the offspring for the next generation has potential consequences for the population dynamics, genetics, and evolution of a group of organisms. High VRS has been described as a normal feature of helminth populations, although studies have focused largely on parasites of vertebrate hosts. Paragordius varius, a parasite of crickets, was used as a model system to study VRS. In this life cycle, worms absorb and store resources for reproduction from their hosts before being released into water. Egg output varied significantly with worm length, indicating that female length is an excellent predictor of fecundity. Analyses using the Lorenz curve and Gini coefficient suggest that there were no marked fecundity differences. This result was supported by data collected from a natural gordiid population, Gordius difficilis, suggesting that within gordiid populations the offspring of the next generation are contributed nearly equally by females. In addition, male body length appeared to be limited by intensity, whereas females showed no length limitation by crowding. These results contrast previous studies of parasites.

'Suicide' of crickets harbouring hairworms: a proteomics investigation

Despite increasing evidence of host phenotypic manipulation by parasites, the underlying mechanisms causing infected hosts to act in ways that benefit the parasite remain enigmatic in most cases. Here, we used proteomics tools to identify the biochemical alterations that occur in the head of the cricket Nemobius sylvestris when it is driven to water by the hairworm Paragordius tricuspidatus. We characterized host and parasite proteomes during the expression of the water-seeking behaviour. We found that the parasite produces molecules from the Wnt family that may act directly on the development of the central nervous system (CNS). In the head of manipulated cricket, we found differential expression of proteins specifically linked to neurogenesis, circadian rhythm and neurotransmitter activities. We also detected proteins for which the function(s) are still unknown. This proteomics study on the biochemical pathways altered by hairworms has also allowed us to tackle questions of physiological and molecular convergence in the mechanism(s) causing the alteration of orthoptera behaviour. The two hairworm species produce effective molecules acting directly on the CNS of their orthoptera hosts.

Artifical transfer and morphological description of virus particles associated with superparasitism behaviour in a parasitoid wasp

In parasitoids, the adaptive significance of superparasitism (laying of egg(s) in already parasitized hosts) has been the subject of strong controversy. The current view is to interpret this behaviour as an adaptation to increased competition for hosts, because the supernumerary egg still has a chance to win possession for the host. However, we recently discovered that in the solitary parasitoid Leptopilina boulardi, superparasitism is rather caused by an unknown infectious element: stable non superparasitizing lineages (NS) are transformed into stable superparasitizing lineages (S) after eggs from both lineages have competed inside the same host (superparasitism). In this report, we investigate the nature and location of the causative agent. Involvement of bacteria is unlikely because antibiotic treatments do not affect wasp phenotype and because bacterial 16S ribosomal DNA was not detected using PCR. We report successful injection experiments showing that the causative agents are located in wasp poison gland and ovaries and are stably inherited. Electron microscopic studies demonstrate that long filamentous virus particles located in wasp oviducts are strongly associated with superparasitism behaviour, leading to reconsider the adaptive significance of this behaviour in parasitoids. Interestingly, parasitoids are often infected with similar viruses for which no phenotypic effect has been documented. This raises the possibility that they could induce the same behavioural manipulation.

The virus infecting the parasitoid Leptopilina boulardi exerts a specific action on superparasitism behaviour

Parasites often induce behavioural changes in their host. However, it is not necessarily easy to determine whether these changes are representative of an adaptation of the parasite (parasite manipulation), an adaptive response of the host or a side-effect of infection. In a solitary parasitoid of Drosophila larvae (Leptopilina boulardi), viral particles (LbFV) modify the host acceptance behaviour of infected females by increasing their tendency to superparasitize. This behavioural alteration allows for the horizontal transmission of the virus within superparasitized Drosophila larvae. To add support for or against the 'manipulation hypothesis', we investigated whether other behavioural components of the parasitoid are affected by viral infection, and whether other forms of horizontal transmission exist. Neither the ability of females to locate host kairomones nor their daily rhythm of locomotor activity was affected by viral infection. However, infected females showed a lower rate of locomotor activity, suggesting a physiological cost of infection. The searching paths of females were also unaffected. Males from infected and uninfected lines showed the same ability to locate females'sexual pheromones. Moreover, alternative modes of horizontal transmission (through food consumption and/or contact with the same Drosophila larvae) did not lead to viral contamination of the parasitoid. The overall specificity of behavioural alteration and of viral horizontal transmission is consistent with the hypothesis that the virus manipulates the behaviour of the parasitoid.

Hairworm anti-predator strategy: a study of causes and consequences

One of the most fascinating anti-predator responses displayed by parasites is that of hairworms (Nematomorpha). Following the ingestion of the insect host by fish or frogs, the parasitic worm is able to actively exit both its host and the gut of the predator. Using as a model the hairworm, Paragordius tricuspidatus, (parasitizing the cricket Nemobius sylvestris) and the fish predator Micropterus salmoïdes, we explored, with proteomics tools, the physiological basis of this anti-predator response. By examining the proteome of the parasitic worm, we detected a differential expression of 27 protein spots in those worms able to escape the predator. Peptide Mass Fingerprints of candidate protein spots suggest the existence of an intense muscular activity in escaping worms, which functions in parallel with their distinctive biology. In a second step, we attempted to determine whether the energy expended by worms to escape the predator is traded off against its reproductive potential. Remarkably, the number of offspring produced by worms having escaped a predator was not reduced compared with controls.

Behavioural manipulation in a grasshopper harbouring hairworm: a proteomics approach

The parasitic Nematomorph hairworm, Spinochordodes tellinii (Camerano) develops inside the terrestrial grasshopper, Meconema thalassinum (De Geer) (Orthoptera: Tettigoniidae), changing the insect's responses to water. The resulting aberrant behaviour makes infected insects more likely to jump into an aquatic environment where the adult parasite reproduces. We used proteomics tools (i.e. two-dimensional gel electrophoresis (2-DE), computer assisted comparative analysis of host and parasite protein spots and MALDI-TOF mass spectrometry) to identify these proteins and to explore the mechanisms underlying this subtle behavioural modification. We characterized simultaneously the host (brain) and the parasite proteomes at three stages of the manipulative process, i.e. before, during and after manipulation. For the host, there was a differential proteomic expression in relation to different effects such as the circadian cycle, the parasitic status, the manipulative period itself, and worm emergence. For the parasite, a differential proteomics expression allowed characterization of the parasitic and the free-living stages, the manipulative period and the emergence of the worm from the host. The findings suggest that the adult worm alters the normal functions of the grasshopper's central nervous system (CNS) by producing certain 'effective' molecules. In addition, in the brain of manipulated insects, there was found to be a differential expression of proteins specifically linked to neurotransmitter activities. The evidence obtained also suggested that the parasite produces molecules from the family Wnt acting directly on the development of the CNS. These proteins show important similarities with those known in other insects, suggesting a case of molecular mimicry. Finally, we found many proteins in the host's CNS as well as in the parasite for which the function(s) are still unknown in the published literature (www) protein databases. These results support the hypothesis that host behavioural changes are mediated by a mix of direct and indirect chemical manipulation.

First analysis of the proteome in two nematomorph species, Paragordius tricuspidatus (Chordodidae) and Spinochordodes tellinii (Spinochordodidae)

The proteome of most parasite species is currently unknown. Hairworms (Nematomorpha), 300 species distributed around the world, are parasitic in arthropods (mainly terrestrial species) when juveniles, but they are free-living in aquatic environments when adult. Most aspects of their systematics and biology are currently unknown. The aim of this paper was (i) to report a novel and reproducible protocol for the analysis of the proteome of hairworms using two-dimensional gel electrophoresis (2-DGE) and mass spectrometry (matrix laser desorption ionization-time of flight mass spectrometry (MALDI-TOF)) and (ii) to determine the level of proteomic divergence between two sympatric but taxonomically unrelated nematomorph species in the adult stage, Paragordius tricuspidatus Dufour (Nematomorpha, Gordiidae) and Spinochordodes tellinii Camerano (Nematomorpha, Gordiidae). In total, 689 protein spots were observed for P. tricuspidatus, 575 for S. tellinii. Only 36.2% spots were shared between the two species. Quantitative analysis of the proteins which are common to both parasite species reveals substantial differences in the pattern of protein expression. These results suggest a rapid evolutionary divergence between these two nematomorph families. Also, to test the value of our MALDI-TOF protocol, we used Actin-2 (Act-2), a protein highly conserved in the course of evolution. Peptide mass fingerprint (PMF) data obtained for Act-2 of P. tricuspidatus and S. tellinii suggest a very high homology with Act-2 of different worms species belonging to the Bilateria phylum (Annelida and Nematoda) and more specifically to Lumbricus terrestris (Annelida, Lumbricidae) and Caenorhabditis elegans (Nematoda, Rhabditidae). We discuss our results in relationship with current ideas concerning the use of proteomics in systematics.