Do brain parasites alter host personality? — Experimental study in minnows

Other Schistosomatoidea and Diplostomoidea

Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis (schistosomiasis) affecting more than 200 million people in tropical and subtropical countries, and infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The "Aporocotylidae" sensu lato are pathogenic in fish, "Spirorchiidae" sensu lato in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in mollusks and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.

Avian malaria parasite infections do not affect personality in the chestnut thrush (Turdus rubrocanus) on the Qinghai-Tibet Plateau

Personality traits, the consistent individual behavioral differences, are currently gaining much attention in studies of natural bird populations. However, associations between personality traits and parasite infections are not often investigated. Even less attention has been given to studies of birds in the high-elevation region such as the Tibetan plateau. This research aims to examine the relationship between avian malaria parasites and two personality traits in a population of the Chestnut Thrush (Turdus rubrocanus) breed in the Tibetan plateau. Our results revealed no evidence of sex bias in malaria parasite prevalence. Furthermore, we found no effect of infection status on two personality scores: activity and boldness. Additionally, no effects on the activity level or boldness were observed for different parasite lineages of Haemoproteus, Leucocytozoon, the sex of the birds, or their interactions. Similarly, we did not find any relationship between activity level and boldness with nestling numbers, sex, or their interactions. Notably, individuals with a larger number of offspring tended to display greater boldness. Our findings indicate that blood parasite infections are common in this population but do not significantly impact the personality of the birds.

Le Petit Machiavellian Prince: Effects of Latent Toxoplasmosis on Political Beliefs and Values

Humans infected by Toxoplasma gondii express no specific symptoms but manifest higher incidence of many diseases, disorders and differences in personality and behavior. The aim of this study was to compare the political beliefs and values of Toxoplasma-infected and Toxoplasma-free participants. We measured beliefs and values of 2315 responders via an online survey (477 Toxoplasma-infected) using the Political Beliefs and Values Inventory (PI34). This study showed Toxoplasma-infected and Toxoplasma-free participants of our cross-sectional study differed in three of four factors of PI34, scoring higher in Tribalism and lower in Cultural liberalism and Anti-Authoritarianism. We found sex differences in political beliefs associated with Toxoplasma infection. Infected women scored higher in tribalism and lower in cultural liberalism, compared with the Toxoplasma-free control group, while infected men scored higher in economic equity. These results fit with sexual differences in behavior and attitude observed after toxoplasmosis infection. Controlling for the effect of worse physical health and mental health had little impact, suggesting that impaired health did not cause these changes. Rather than adaptation to prevalence of parasites, as suggested by parasite-stress theory, the differences might be side-effects of long-term mild inflammatory reaction. However, to get clear picture of the mild inflammation effects, more research focused on different infectious diseases is needed.

Parasites differentially impact crayfish personality in different contexts

The expression of an individual animal’s behaviour can be placed along many different personality spectra. Parasite load can alter animal behaviour and, thus, fitness. The personality traits of rusty crayfish, Faxonius rusticus, were analysed in three different behavioural contexts: foraging, exploration, and threatened. Each crayfish was tested in each context 3 times, giving a total of 9 assays per crayfish. After assays were completed, crayfish were dissected, and the hepatopancreas of each crayfish was photo analysed to determine the parasite load of the trematode, Microphallus spp. A composite personality score for each assay and parasite load was loaded into a PCA. The PCA model showed that as parasite load increased, crayfish became bolder in threatening contexts and less exploratory in novel environments, whether or not a food stimulus was present. Thus, parasite load alters the placement of crayfish on different personality spectra, but this change is context specific.

Animal behavior and animal personality from a non-human perspective: Getting help from the machine

We can now track the position of every fly's leg or immerse a tiny fish inside a virtual world by monitoring its gaze in real time. Yet capturing animals' posture or gaze is not like understanding their behavior. Instead, behaviors are still often interpreted by human observers in an anthropomorphic manner. Even newer tools that automatically classify behaviors rely on human observers for the choice of behaviors. In this perspective, we suggest a roadmap toward a "human-free" interpretation of behavior. We present several recent advances, including our recent work on animal personalities. Personality both underlies behavioral differences among individuals and is consistent over time. A mathematical formulation of this idea has allowed us to measure mouse traits objectively, map behaviors across species (humans included), and explore the biological basis of behavior. Our goal is to enable "machine translation" of raw movement data into intelligible human concepts en route to improving our understanding of animals and people.

Do parasites influence behavioural traits of wild and hatchery-reared Murray cod, Maccullochella peelii?

This study aimed to investigate the links between parasites and behavioural traits of juvenile Murray cod (Maccullochella peelii). The Murray cod is an endangered Australian freshwater fish for which restocking programs are in place and there is a growing human consumption market. However, little is known about the parasites of these fish and how these parasites influence their behaviour and survival. Fingerlings and yearling fish were sourced from a hatchery and the wild, and after acclimatisation in the laboratory, variation in behavioural traits was examined using emergence, exploration and predator inspection tests. The fish were then euthanised to determine their age and examined for infection with parasites. Wild fish had more camallanid nematodes and lernaeid copepods than hatchery fish. An information theoretic approach using Akaike's Information Criterion (AIC) indicated that infection with protozoan cysts was an important factor for predicting the latency to emerge and explore a new environment, which was interpreted as reduced "boldness". In contrast, the presence of lernaeid copepods was included in two of the four best models predicting predator inspection, indicating that infected fish were less likely to inspect a predator. Source of fish (wild or hatchery) was found to be a strong influence on behavioural responses in all our tests. All parasites found in the present study are known to result in clinical signs of diseases in their fish hosts, raising the possibility that responses in tests of behavioural traits reflect side effects of infection. Additionally, the effect of host adaptation to not show signs of parasite infection, or more simply that the effects on behaviour are subtle and difficult to reveal with small sample sizes, is discussed. Nonetheless, we propose that it is important that infection with parasites is considered in fish behavioural studies both to assess survival behaviour and to avoid misinterpretation of behavioural tests of animal personality.

Potential multidimensional behavioural impacts of differential infection in two fish populations

Parasites can influence the behaviour of their hosts, however investigations on how they may shape multiple personality traits are uncommon. The flatworm parasite Tylodelphys darbyi resides in the eyes of common bully, Gobiomorphus cotidianus, a locally common fish host to a range of other parasites that could also influence their behaviour. Here we assess how parasitism may be related to personality traits of two G. cotidianus populations; one where T. darbyi is highly abundant and one where the parasite is absent. We hypothesized that T. darbyi would have a stronger association with the different personality traits than other parasite taxa, and that the effects of infection on personality traits would vary between populations. Our results demonstrate that T. darbyi infections correlate with boldness, exploration, and activity within and among individuals. Further, we show that the relationship and therefore possible influence of other parasites, e.g., Apatemon sp., on personality traits vary between two host populations. Our study has revealed potential patterns highlighting how parasitism may differentially contribute to behavioural and ecological divergence among host populations.

Spillover of an alien parasite reduces expression of costly behaviour in native host species

Understanding the effects of invasive alien species (IAS) on native host-parasite relationships is of importance for enhancing ecological theory and IAS management. When IAS and their parasite(s) invade a guild, the effects of interspecific resource competition and/or parasite-mediated competition can alter existing native host-parasite relationships and the dependent biological traits such as native species' behaviour. We used a natural experiment of populations of native red squirrels Sciurus vulgaris that were colonized by the alien grey squirrel Sciurus carolinensis, comparing repeated measurements of red squirrel parasite infection and personality with those taken in sites where only the native species occurred. We explored two alternative hypotheses: (a) individual differences in personality traits (activity and/or sociability) of native red squirrel positively affect the probability of macroparasite spillover and thus the likelihood to acquire the alien's parasitic helminth Strongyloides robustus; (b) the combined effects of grey squirrel presence and parasite infection result in a reduction of costly personality traits (activity and/or exploration). Using data from 323 arena tests across three experimental (native species and IAS) and three control sites (only native species), we found negative correlations between native species' activity and infection with S. robustus in the sites invaded by the alien species. Activity was also negatively correlated with infection by its native helminth Trypanoxyuris sciuri but only when grey squirrels were present, while in the red-only sites there was no relationship of T. sciuri infection with any of the personality traits. Moreover, individuals that acquired S. robustus during the study reduced their activity after infection, while this was not the case for animals that remained uninfected. Our results show that parasite-mediated competition is costly, reducing activity in individuals of the native species, and altering the native host-native parasite relationships.

Personality Influences Risk of Parasitism in Fish

Influence of fish personality on infection rate is poorly studied. In the experiments on young-of-the-year Oncorhynchus mykiss and cercariae of the trematode Diplostomum pseudospathaceum, we tested the hypothesis that infection rate differs between more and less active ("bold" and "shy") fish. Will individual differences in infection persist upon re-infection? Fish serve as a second intermediate host for this trematode. Positive correlation was found between the results of consecutive infections. Accumulation of parasites with successive infections leads to an aggregated distribution of D. pseudospathaceum among the hosts, affecting individual fitness and polymorphism in fish populations. Persistent individual differences in parasite burden among fish and, as a result, vulnerability for predators confirms the role of parasites as an important factor of natural selection.

Schistosomatoidea and Diplostomoidea

Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis affecting more than 200 million people in tropical and subtropical countries, infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The Aporocotylidae are pathogenic in fish, Spirorchiidae in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in molluscs and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive, but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.

Parasite infection and host personality: Glugea-infected three-spined sticklebacks are more social

Abstract

The existence of animal personality is now well-documented, although the causes and consequences of this phenomenon are still largely unclear. Parasite infection can have pervasive effects on hosts, including altering host behaviour, and may thus contribute to differences in host personality. We investigated the relationship between the three-spined stickleback and its common parasite Glugea anomala, with focus on differences in host personality. Naturally infected and uninfected individuals were assayed for the five personality traits activity, exploration, boldness, sociability, and aggression. If infected fish behaved differently from uninfected, to benefit this parasite with horizontal transmission, we predicted behaviour increasing interactions with other sticklebacks to increase. Infection status explained differences in host personality. Specifically, Glugea-infected individuals were more social than uninfected fish. This confirms a link between parasite infection and host behaviour, and a relationship which may improve the horizontal transmission of Glugea. However, future studies need to establish the consequences of this for the parasite, and the causality of the parasite-host personality relationship.

Significance statement

Parasite infection that alters host behaviour could be a possible avenue of research into the causes of animal personality. We studied the link between infection and personality using the three-spined stickleback and its parasite Glugea anomala. We predicted that infected individuals would be more prone to interact with other sticklebacks, since this would improve transmission of this parasite. The personality of uninfected and naturally infected fish was measured and we observed that Glugea-infected sticklebacks were more social. Our results confirm a link between parasitism and variation in host personality.

Electronic supplementary material

The online version of this article (10.1007/s00265-018-2586-3) contains supplementary material, which is available to authorized users.

The effect of parasitism on personality in a social insect

Individuals are known to differ consistently in various aspects of their behaviour in many animal species, a phenomenon that has come to be referred to as animal personalities. These individual differences are likely to have evolutionary and ecological significance, and it is therefore important to understand the precise nature of how environmental and physiological factors affect animal personalities. One factor which may affect personality is disease, but while the effects of disease on many aspects of host behaviour are well known, the effects on animal personalities have been little studied. Here we show that wood ants, Formica rufa, exhibit consistent individual differences in three personality traits: boldness, sociability and aggressiveness. However, experimental exposure to a virulent fungal parasite, Metarhizium pingshaense, had surprisingly little effect on the personality traits. Parasite-challenged ants showed marginal changes in sociability at high doses of parasite but no change in boldness or aggressiveness even when close to death. There was similarly little effect of other physiological stresses on ant personalities. The results suggest that individual personality in ants can be remarkably resilient to physiological stress, such as that caused by parasite infection. Future studies are needed to determine whether there is a similar resilience in solitary animals, as well as in other social species.

Experience during development triggers between-individual variation in behavioural plasticity

Behavioural consistency within and across behaviours (animal personality and behavioural syndrome, respectively) has been vigorously studied in the last decade, leading to the emergence of "animal personality" research. It has been proposed recently that not only mean behaviour (behavioural type), but the environmentally induced behavioural change (behavioural plasticity) might also differ between individuals within populations. While case studies presenting between-individual variation in behavioural plasticity have started to accumulate, the mechanisms behind its emergence are virtually unknown. We have recently demonstrated that ecologically relevant environmental stimuli during ontogeny are necessary for the development of animal personality and behavioural syndromes. However, it is unknown whether between-individual variation in behavioural plasticity is hard-wired or induced. Here, we tested whether experience with predation during development affected predator-induced behavioural plasticity in Rana dalmatina tadpoles. We ran a common garden experiment with two ontogenetic predation treatments: tadpoles developed from hatching in either the presence or absence of olfactory predator stimuli. Then, we assayed all tadpoles repeatedly for activity and risk-taking both in the absence and presence of olfactory predator stimuli. We found that (a) between-individual variation in predator-induced behavioural plasticity was present only in the group that developed in the presence of olfactory stimuli from predators and (b) previous experience with predatory stimuli resulted in lower plastic response at the group level. The latter pattern resulted from increased between-individual variation and not from universally lower individual responses. We also found that experience with predation during development increased the predictability (i.e. decreased the within-individual variation unrelated to environmental change) of activity, but not risk-taking. In line with this, tadpoles developing under perceived predatory risk expressed their activity with higher repeatability. We suggest that ecologically relevant environmental stimuli are not only fundamental for the development of animal personality and behavioural syndromes, but also for individual variation in behavioural plasticity. Thus, experience is of central importance for the emergence of individual behavioural variation at many levels.

Personality differentially affects individual mate choice decisions in female and male Western mosquitofish (Gambusia affinis)

Consistent individual differences in behavioral tendencies (animal personality) can affect individual mate choice decisions. We asked whether personality traits affect male and female mate choice decisions similarly and whether potential personality effects are consistent across different mate choice situations. Using western mosquitofish (Gambusia affinis) as our study organism, we characterized focal individuals (males and females) twice for boldness, activity, and sociability/shoaling and found high and significant behavioral repeatability. Additionally, each focal individual was tested in two different dichotomous mate choice tests in which it could choose between computer-animated stimulus fish of the opposite sex that differed in body size and activity levels, respectively. Personality had different effects on female and male mate choice: females that were larger than average showed stronger preferences for large-bodied males with increasing levels of boldness/activity (i.e., towards more proactive personality types). Males that were larger than average and had higher shoaling tendencies showed stronger preferences for actively swimming females. Size-dependent effects of personality on the strength of preferences for distinct phenotypes of potential mating partners may reflect effects of age/experience (especially in females) and social dominance (especially in males). Previous studies found evidence for assortative mate choice based on personality types or hypothesized the existence of behavioral syndromes of individuals’ choosiness across mate choice criteria, possibly including other personality traits. Our present study exemplifies that far more complex patterns of personality-dependent mate choice can emerge in natural systems.

Three Strigeid cercariae from Littorina littorea snail, Qarun Lake, Fayoum, Egypt

Aim:

The present study aims to focus on the role of common marine snails (Littorina littorea) as a vector for some trematode parasites.

Materials and Methods:

A total of 327 marine water L. littorea snails were collected during the summer of 2016 from a Qarun lake in the EL-Fayoum Governorate, Egypt. The snails were investigated for infection by trematode parthenitae through induction of cercarial shedding by exposure to light and crushing the snails. The species were stored in Search Laboratory of Zoology Department, Faculty of Science, Fayoum University.

Results:

Three species of Strigeid littorina cercaria were identified from the infected snails. They are described here and they identified in relation to close-up morphological features and linked to its snail hosts. They give the following names: Cercaria strigeid littorina type 1, C. strigeid littorina type 2, and C. strigeid littorina type 3. The incidence of infection by these cercariae was 33%, 25.7%, and 2.4%, respectively.

Conclusion:

This study is clarifying the importance of this marine snail as intermediate hosts for new trematode species.

Modification of host social networks by manipulative parasites

Social network models provide a powerful tool to estimate infection risk for individual hosts and track parasite transmission through host populations. Here, bringing together concepts from social network theory, animal personality, and parasite manipulation of host behaviour, I argue that not only are social networks shaping parasite transmission, but parasites in turn shape social networks through their effects on the behaviour of infected individuals. Firstly, I review five general categories of behaviour (mating behaviour, aggressiveness, activity levels, spatial distribution, and group formation) that are closely tied to social networks, and provide evidence that parasites can affect all of them. Secondly, I describe scenarios in which behaviour-altering parasites can modify either the role or position of individual hosts within their social network, or various structural properties (e.g., connectance, modularity) of the entire network. Experimental approaches allowing comparisons of social networks pre- versus post-infection are a promising avenue to explore the feedback loop between social networks and parasite infections.

Temperature modulates the interaction between fungicide pollution and disease: evidence from a Daphnia-microparasitic yeast model

Temperature is expected to modulate the responses of organisms to stress. Here, we aimed to assess the influence of temperature on the interaction between parasitism and fungicide contamination. Specifically, using the cladoceran Daphnia as a model system, we explored the isolated and interactive effects of parasite challenge (yeast Metschnikowia bicuspidata) and exposure to fungicides (copper sulphate and tebuconazole) at two temperatures (17 and 20 °C), in a fully factorial design. Confirming a previous study, M. bicuspidata infection and copper exposure caused independent effects on Daphnia life history, whereas infection was permanently suppressed with tebuconazole exposure. Here, we show that higher temperature generally increased the virulence of the parasite, with the hosts developing signs of infection earlier, reproducing less and dying at an earlier age. These effects were consistent across copper concentrations, whereas the joint effects of temperature (which enhanced the difference between non-infected and infected hosts) and the anti-parasitic action of tebuconazole resulted in a more pronounced parasite × tebuconazole interaction at the higher temperature. Thus, besides independently influencing parasite and contaminant effects, the temperature can act as a modulator of interactions between pollution and disease.

Maternal effects in vulnerability to eye-parasites and correlations between behavior and parasitism in juvenile Arctic charr

Hatchery‐reared fish show high mortalities after release to the wild environment. Explanations for this include potentially predetermined genetics, behavioral, and physiological acclimation to fish farm environments, and increased vulnerability to predation and parasitism in the wild. We studied vulnerability to Diplostomum spp. parasites (load of eye flukes in the lenses), immune defense (relative spleen size) and antipredator behaviors (approaches toward predator odor, freezing, and swimming activity) in hatchery‐reared juvenile Arctic charr (Salvelinus alpinus) using a nested mating design. Fish were exposed to eye‐fluke larvae via the incoming water at the hatchery. Fish size was positively associated with parasite load, but we did not find any relationship between relative spleen size and parasitism. The offspring of different females showed significant variation in their parasite load within sires, implying a dam effect in the vulnerability to parasites. However, the family background did not have any effect on spleen size. In the mean sire level over dams, the fish from the bolder (actively swimming) families in the predator trials suffered higher loads of eye flukes than those from more cautiously behaving families. Thus, the results indicate potentially maternally inherited differences in vulnerability to eye‐fluke parasites, and that the vulnerability to parasites and behavioral activity are positively associated with each other at the sire level. This could lead to artificial and unintentional selection for increased vulnerability to both parasitism and predation if these traits are favored in fish farm environments.

Environment-dependence of behavioural consistency in adult male European green lizards (Lacerta viridis)

Understanding the background mechanisms affecting the emergence and maintenance of consistent between-individual variation within population in single (animal personality) or across multiple (behavioural syndrome) behaviours has key importance. State-dependence theory suggests that behaviour is ‘anchored’ to individual state (e.g. body condition, gender, age) and behavioural consistency emerges through behavioural-state feedbacks. A number of relevant state variables are labile (e.g. body condition, physiological performance) and expected to be affected by short-term environmental change. Yet, whether short-term environmental shifts affect behavioural consistency during adulthood remains questionable. Here, by employing a full-factorial laboratory experiment, we explored if quantity of food (low vs. high) and time available for thermoregulation (3h vs. 10h per day) had an effect on activity and risk-taking of reproductive adult male European green lizards (Lacerta viridis). We focussed on different components of behavioural variation: (i) strength of behavioural consistency (repeatability for animal personality; between-individual correlation for behavioural syndrome), (ii) behavioural type (individual mean behaviour) and (iii) behavioural predictability (within-individual behavioural variation). Activity was repeatable in all treatments. Risk-taking was repeatable only in the low basking treatments. We found significant between-individual correlation only in the low food × long basking time group. The treatments did not affect behavioural type, but affected behavioural predictability. Activity predictability was higher in the short basking treatment, where it also decreased with size (≈ age). Risk-taking predictability in the short basking treatment increased with size under food limitation, but decreased when food supply was high. We conclude that short-term environmental change can alter various components of behavioural consistency. The effect could be detected in the presence/absence patterns of animal personality and behavioural syndrome and the level of individual behavioural predictability, but not in behavioural type.

Does exploratory behavior or activity in a wild mouse explain susceptibility to virus infection?

Exploration and activity are often described as trade-offs between the fitness benefits of gathering information and resources, and the potential costs of increasing exposure to predators and parasites. More exploratory individuals are predicted to have higher rates of parasitism, but this relationship has rarely been examined for virus infections in wild populations. Here, we used the multimammate mouse Mastomys natalensis to investigate the relationship between exploration, activity, and infection with Morogoro virus (MORV). We characterized individual exploratory behavior (open field and novel object tests) and activity (trap diversity), and quantified the relationship between these traits and infection status using linear regression. We found that M. natalensis expresses consistent individual differences, or personality types, in exploratory behavior (repeatability of 0.30, 95% CI: 0.21–0.36). In addition, we found a significant contrasting effect of age on exploration and activity where juveniles display higher exploration levels than adults, but lower field-activity. There was however no statistical evidence for a behavioral syndrome between these 2 traits. Contrary to our expectations, we found no correlation between MORV infection status and exploratory behavior or activity, which suggests that these behaviors may not increase exposure probability to MORV infection. This would further imply that variation in viral infection between individuals is not affected by between-individual variation in exploration and activity.

Consequences of eye fluke infection on anti-predator behaviours in invasive round gobies in Kalmar Sound

Larvae of the eye fluke, Diplostomum, emerge from snails and infect fish by penetrating skin or gills, then move to the lens where they may impair the vision of the fish. For the fluke to reproduce, a bird must eat the infected fish, and it has been suggested that they therefore actively manipulate the fish's behaviour to increase the risk of predation. We found that round gobies Neogobius melanostomus, a species that was recently introduced to the Kalmar Sound of the Baltic Sea, had an eye fluke prevalence of 90-100%. We investigated how the infection related to behavioural variation in round gobies. Our results showed that the more intense the parasite-induced cataract, the weaker the host's response was to simulated avian attack. The eye flukes did not impair other potentially important anti-predator behaviours, such as shelter use, boldness and the preference for shade. Our results are in accordance with the suggestion that parasites induce changes in host behaviour that will facilitate transfer to their final host.

Adult bacterial exposure increases behavioral variation and drives higher repeatability in field crickets

Among-individual differences in behavior are now a widely studied research-focus within the field of behavioral ecology. Furthermore, elements of an animal's internal state, such as energy or fat reserves, and infection status can have large impacts on behaviors. Despite this, we still know little regarding how state may affect behavioral variation. Recent exposure to pathogens may have a particularly large impact on behavioral expression given that it likely activates costly immune pathways, potentially forcing organism to make behavioral tradeoffs. In this study we investigate how recent exposure to a common bacterial pathogen, Serratia marcescens, affects both the mean behavioral expression and the among-individual differences (i.e. variation) in boldness behavior in the field cricket, Gryllus integer. We find that recent pathogen exposure does not affect mean behavioral expression of the treatment groups, but instead affects behavioral variation and repeatability. Specifically, bacterial exposure drove large among-individual variation, resulting in high levels of repeatability in some aspects of boldness (willingness to emerge into a novel environment), but not others (latency to become active in novel environment), compared to non-infected crickets. Interestingly, sham injection resulted in a universal lack of among-individual differences. Our results highlight the sensitivity of among-individual variance and repeatability estimates to ecological and environmental factors that individuals face throughout their lives.

Individual differences in boldness influence patterns of social interactions and the transmission of cuticular bacteria among group-mates

Despite the importance of host attributes for the likelihood of associated microbial transmission, individual variation is seldom considered in studies of wildlife disease. Here, we test the influence of host phenotypes on social network structure and the likelihood of cuticular bacterial transmission from exposed individuals to susceptible group-mates using female social spiders (Stegodyphus dumicola). Based on the interactions of resting individuals of known behavioural types, we assessed whether individuals assorted according to their behavioural traits. We found that individuals preferentially interacted with individuals of unlike behavioural phenotypes. We next applied a green fluorescent protein-transformed cuticular bacterium,Pantoeasp., to individuals and allowed them to interact with an unexposed colony-mate for 24 h. We found evidence for transmission of bacteria in 55% of cases. The likelihood of transmission was influenced jointly by the behavioural phenotypes of both the exposed and susceptible individuals: transmission was more likely when exposed spiders exhibited higher 'boldness' relative to their colony-mate, and when unexposed individuals were in better body condition. Indirect transmission via shared silk took place in only 15% of cases. Thus, bodily contact appears key to transmission in this system. These data represent a fundamental step towards understanding how individual traits influence larger-scale social and epidemiological dynamics.

The common neural parasite Pseudoloma neurophilia is associated with altered startle response habituation in adult zebrafish (Danio rerio): Implications for the zebrafish as a model organism

The zebrafish's potential as a model for human neurobehavioral research appears nearly limitless despite its relatively recent emergence as an experimental organism. Since the zebrafish has only been part of the research community for a handful of decades, pathogens from its commercial origins continue to plague laboratory stocks. One such pathogen is Pseudoloma neurophilia, a common microparasite in zebrafish laboratories world-wide that generally produces subclinical infections. Given its high prevalence, its predilection for the host's brain and spinal cord, and the delicate nature of neurobehavioral research, the behavioral consequences of subclinical P. neurophilia infection must be explored. Fish infected via cohabitation were tested for startle response habituation in parallel with controls in a device that administered ten taps over 10 min along with taps at 18 and 60 min to evaluate habituation extinction. After testing, fish were euthanized and evaluated for infection via histopathology. Infected fish had a significantly smaller reduction in startle velocity during habituation compared to uninfected tankmates and controls. Habituation was eliminated in infected and control fish at 18 min, whereas exposed negative fish retained partial habituation at 18 min. Infection was also associated with enhanced capture evasion: Despite the absence of external symptoms, infected fish tended to be caught later than uninfected fish netted from the same tank. The combination of decreased overall habituation, early extinction of habituation compared to uninfected cohorts, and enhanced netting evasion indicates that P. neurophilia infection is associated with a behavioral phenotype distinct from that of controls and uninfected cohorts. Because of its prevalence in zebrafish facilities, P. neurophilia has the potential to insidiously influence a wide range of neurobehavioral studies if these associations are causative. Rigorous health screening is therefore vital to the improvement of the zebrafish as a translational model for human behavior.

Parasites and personality in periwinkles (Littorina littorea): Infection status is associated with mean-level boldness but not repeatability

We demonstrate the presence of animal personality in an inter-tidal gastropod, Littorina littorea, both in a sample of individuals infected by the trematode Cryptocotyle lingua and in an uninfected sample. On average infected individuals behaved more cautiously than individuals free of infection, but the parasite did not affect repeatability. Although the parasite is not associated with greater diversity of behaviour amongst infected individuals, infection might be associated with state-dependent personality differences between infected and non-infected individuals.