Journal of Animal Ecology

Grouping with others can provide enhanced information about resources and threats. A key hypothesis in social evolution proposes that individuals can benefit from social information in environments where it is challenging to meet energetic needs. Here, we test this hypothesis by examining the environmental drivers of conspecific flocking behaviour in a large archive of citizen science observations of two common North American birds, the dark-eyed junco (Junco hyemalis) and black-capped chickadee (Poecile atricapillus). To quantify flocking behaviour, we apply the index of dispersion, D, as a metric of clumpiness in each species spatiotemporal distribution. We show that juncos in winter are nearly always more clustered than a random expectation, whereas chickadees span a range from uniform to socially clustered distributions. In both species, the degree of social clustering strongly increases with abundance. We identify several key environmental variables that explain the extent of conspecific flocking in both species. Flocks are more socially clustered at higher latitudes, higher elevations, closer to midwinter, and at temperatures that are colder than average given the location and time of year. Together, these findings support the hypothesis that sociality is a key strategy for coping with harsh environments. HIGHLIGHTSO_LIGrouping with others can be an important source of information about resources C_LIO_LIWe analyzed how flocking behaviour changes throughout winter in two bird species C_LIO_LIWe used the index of dispersion to quantify social clustering at a broad scale C_LIO_LIIn both species, social clustering increases in response to climate challenges C_LI

Habitat loss and disease outbreak play a major role in the decline of biodiversity. Habitat degradation is often associated with reduced food resources, which can lead to less investment in host immunity and increased infections. However, pathogens use host resources for replication and pathogen traits, such as infecting hosts internally or short generation times, might allow pathogens to rapidly capitalize on host-consumed nutrients. Thus, it is unclear whether increased food consumption by hosts should reduce or amplify pathogen levels. We conducted experiments on Cuban treefrogs (Osteopilus septentrionalis) to test how food availability affects infection levels of Ranavirus and the fungal pathogen Batrachochytrium dendrobatidis (Bd), which are both associated with mass die-offs of amphibians. Given that Ranavirus is an endoparasite with a much shorter generation time than the ectoparasitic Bd, we postulated that Ranavirus might be able to capitalize on host-consumed resources more quickly than Bd. We hypothesized that increased food availability to hosts might reduce Bd infections more than Ranavirus infections. As predicted, augmenting food access decreased Bd infection intensity, but increased Ranavirus infection intensity. Future work should assess whether pathogen traits, such as generation time and endo- versus ectoparasitism, generally affect whether food resources more positively benefit hosts or pathogens.

The gut microbiome (hereafter, GM) varies across individuals of the same species and this pattern has been observed in multiple wild species. Evidence shows that the GM connects to individual health and survival especially in captive species, but more research is needed to understand how the GM connects to host fitness in wild species. We used long-term monitoring data to investigate whether the GM of collared flycatchers Ficedula albicollis associates with annual and lifetime reproductive success (LRS), and survival to the following breeding season. This is the first study that 1) characterized the collared flycatcher GM, and 2) investigated how variation in the GM related to LRS in wild birds. Our results showed that higher GM diversity was associated with a higher annual and lifetime reproductive success in especially male collared flycatchers. We also found that the compositional variation in collared flycatcher GMs was explained by sex, age, and breeding habitat, but not by annual or lifetime reproductive success. Individuals that died before the next breeding season had higher abundances of ASVs belonging to the pathogenic families Enterobacteriaceae and Parachlamydiaceae, and the genera Corynebacteria and Sphingomonas. Our results show that the GM associates with different aspects of host fitness in a wild bird population. More research is needed to evaluate if there is a causal relationship between the GM and individual fitness. These findings also contribute to our understanding of the GMs role in evolution by elucidating the connection between the GM (trait) and reproductive success.

Much ecological research focuses on phenomena where a given variable can affect another either directly or indirectly through the effect of one or more intervening variables. While various methods to quantify the magnitude of these effects are available, they can be difficult to interpret in a meaningful way, especially for indirect effects. Studies thus often quantity direct effects and infer indirect ones more or less formally. We propose a method for visualizing indirect effects by means of plotting model predictions of an outcome in the presence of both exposure and mediator variables. We demonstrate the method through simulations and apply them to a real-world example involving Tree Swallows (Tachycineta bicolor) and their obligatory hematophagous ectoparasites, Protocalliphora bird blowflies (Diptera: Calliphoridae). Our procedure, which can be seamlessly integrated into an analysts workflow using commonplace software, should prove instrumental to disentangle and interpret relationships among variables involved in ecological mechanisms.

Social living often confers substantial fitness benefits; however, close spatial association among individuals can also elevate opportunities for pathogen transmission, especially where the populations are dense. Despite this, the extent to which avoidance behaviours are expressed by wild reptiles facing fungal disease remains unclear. We examined Eastern Water Dragons (EWDs; Intellagama lesueurii) in Roma Street Parklands, Brisbane, Australia, where a population is affected by the emerging fungal pathogen Nannizziopsis barbatae (Nb). Using a five-year dataset (2018-2023) spanning 146 individuals, we quantified social distance, as the minimum distance to the nearest neighbour, in relation to the number of diseased conspecifics that overlapped each individuals seasonal core home area. Social distance decreased as diseased conspecifics became more numerous, indicating a strong crowding effect; however, this reduction was weaker for diseased individuals, which maintained larger distances than healthy individuals even under high disease pressure. Together, these patterns support partial social avoidance consistent with behavioural changes in infected individuals, suggesting that infection risk constrains density-driven proximity. Our findings provide new insights into how disease pressure shapes social spacing in reptiles and contribute to a broader understanding of behavioural responses to emerging infectious fungal diseases.

Understanding where and when pathogens occur in the environment has implications for reservoir population health and infection risk. In reservoir hosts, infection status and pathogen shedding are affected by processes interacting across different scales: from landscape features affecting host location and transmission to within-host processes affecting host immunity and infectiousness. While uncommonly done, simultaneously incorporating processes across multiple scales may improve pathogen shedding predictions. In Australia, the black flying fox (Pteropus alecto) is a natural host for the zoonotic Hendra virus, which is hypothesized to cause latent infections in bats. Re-activation and virus shedding may be triggered by poor host condition, leading to virus excretion through urine. Here, we developed a statistical modeling approach that combined data at multiple spatial and temporal scales to capture ecological and biological processes potentially affecting virus shedding. We parameterized these models using existing datasets and compared model performance to under-roost virus shedding data from 2011-2014 in 23 roosts across a 1200-km transect. Our approach enabled comparisons among multiple model structures to determine which variables at which scales are most influential for accurate predictions of virus shedding in space and time. We identified environmental predictors and temporal lags of these features that were important for determining where reservoirs are located and multiple independent proxies for reservoir condition. The best-performing multi-scale model delineated periods of low and high virus prevalence, reflecting observed shedding patterns from pooled under-roost samples. Incorporating regional indicators of food scarcity enhanced model accuracy while incorporating other stress indicators at local scales confounded this signal. This multiscale modeling approach enabled the combination of processes from different ecological scales and identified environmental variables influencing Hendra virus shedding, highlighting how integrating data across scales may improve risk forecasts for other pathogen systems.

The social environment has diverse consequences for individuals welfare, health, reproductive success, and survival. This environment consists of different kinds of dyadic bonds that exist at different levels; in many social species, smaller social units come together in larger groups, creating multilevel societies. In great tits (Parus major), individuals have four major types of dyadic bonds: pair mates, breeding neighbours, flockmates, and spatial associates, all of which have been previously linked to fitness outcomes. Here, we show that these different types of dyadic bonds are differentially linked with subsequent reproductive success metrics in this wild population and that considering spatial effects provides further insights into these relationships. We provide evidence that more social individuals had a higher number of fledglings, and individuals with more spatial associates had smaller clutch sizes. We also show individuals with stronger bonds with their pair mate had earlier lay dates. Our study highlights the importance of considering different types of dyadic relationships when investigating the relationship between wellbeing and sociality, and the need for future work aimed at experimentally testing these relationships, particularly in spatially structured populations.

Environmental factors, such as elevated temperature, can have varying effects on hosts and their parasites, which can have consequences for disease outcomes. The individual direct effects of temperature must be disentangled to determine the net-effect in host-parasite relationships, yet few studies have determined the net-effects in a multi-host system. To address this gap, we experimentally manipulated temperature and parasite presence in the nests of two host species infested by parasitic blowflies (Protocalliphora sialia). We conducted a factorial experiment by increasing temperature (or not) and removing all parasites (or not) in the nests of eastern bluebirds (Sialia sialis) and tree swallows (Tachycineta bicolor). We then measured nestling morphometrics, blood loss, and survival and quantified parasite abundance. We predicted that if temperature had a direct effect on parasite fitness, then elevated temperature would cause similar directional effects on parasite abundance across host species. If temperature had a direct effect on hosts, and therefore an indirect effect on the parasite, parasite abundance would differ across host species. Heated swallow nests had fewer parasites compared to non-heated nests. In contrast, heated bluebird nests had more parasites compared to non-heated nests. The results of our study demonstrate that elevated temperature can have differential effects on host species, which can impact infestation susceptibility. Furthermore, changing climates could have complex net-effects on parasite fitness and host health across multi-host-parasite interactions.

O_LISeasonal forcing is a dominant factor shaping host-pathogen interactions and disease dynamics across many wildlife systems, including species impacted by environmentally transmitted parasites. How seasonality in parasite dynamics translates to the host when the infection and disease impacts operate at different timescales, however, remains poorly understood. C_LIO_LIWe investigate how seasonality shapes sarcoptic mange in bare-nosed wombats, Vombatus ursinus, a disease caused by the environmentally transmitted parasitic mite Sarcoptes scabiei, causing a protracted clinical time-course in the host. Using an empirically informed state-based deterministic model we explore how wombat population trajectories are influenced by (i) seasonal constraints to mite survival and (ii) in context of host-pathogen encounter rates, as measured by the ratio of burrows to wombats. C_LIO_LIWe demonstrate three long-term outcomes of wombat-mange: host and parasite extinction, endemic disease, and disease-free. We find seasonal environments narrow the range of host-pathogen encounter rates that support S. scabiei persistence relative to stable environments, and prevalence and population sizes vary more in seasonal compared to stable environments except under moderate host-pathogen encounter rates when seasonal effects are less apparent. We also find that a protracted infectious period is essential for host-parasite coexistence in the wombat-mange system. C_LIO_LIOur seasonal model results are consistent with field observations, such that mange prevalence in natural populations increases during seasons of longer off-host mite survival. Application of these findings suggest management efforts could reduce host population impacts through disease management in seasons with longer off-host parasite survival or reduce the environmental reservoir through disease management in seasons with shorter off-host survival. C_LIO_LIWe provide novel, mechanistic explanations for distinctive population trajectories that arise from a seasonally forced wildlife disease, including climate factors that operate independently on parasites, host demography, and disparate timescales over which seasonality affects parasites and hosts. Broadly, linking seasonality to long-term population dynamics can improve the predictability and management of wildlife diseases, but requires an understanding of how local intrinsic factors interact with seasonal pressures over time. C_LI

Resource competition and parasite exposure both present common density-dependent fitness costs for wild animals. Because launching effective immune responses is costly in terms of resources, parasites fitness costs should be further exacerbated in high-density, resource-depleted areas. To disentangle these relationships, we related density, parasitism, and resource availability to survival and fecundity across lifespan in a long-term study of wild red deer. All fitness measures declined with a combination of parasite count, greater density, and reduced resource availability. Beyond these relationships, as expected, local density and resource scarcity exacerbated survival costs of parasitism in calves, effectively undermining tolerance of infection. However, these synergistic relationships faded in yearlings and then reversed in adults, likely through age-structured selection biases. These findings emphasize that the costs of parasites and resource scarcity can be synergistic and intertwined with density in wild populations, accentuating the value of incorporating resource competition when examining parasite-dependent population regulation.

Gut microbial communities regulate host physiology and health of humans and laboratory animals. The functional significance of these collective bacterial genomes (i.e. the microbiome) to the adaptive potential of wildlife hosts is still unknown. Studies demonstrating convincing examples of microbial flexibility to environmental change so far lack the experimental approaches to demonstrate the effect on host physiology. Invasive species provide natural experiments to tease apart these host-microbe relationships. However, no studies have investigated how microbial symbionts might mediate responses of invasive hosts physiology to environmental change. In this study, we examine whether invasive gut microbiomes have significantly diverged in their ability to respond to novel environmental change (i.e. a dietary challenge) compared to native gut microbiomes by performing reciprocal faecal microbial transplant (FMT) experiments in native and invasive guttural toad (Sclerophrys gutturalis) populations. Subsequently, we determine how the microbiome regulates host physiological changes in response to a dietary challenge. We show that invasive gut microbiomes exhibit higher microbial compositional and predicted functional flexibility to novel dietary change, compared to native gut microbiomes. This increased microbial flexibility is coupled with significant flexibility in energy harvesting. Furthermore, our results indicate that overall invasive gut microbiomes significantly upregulate energy harvesting and physiological performance of hosts, compared to native microbiomes. Our study is the first identifying gut microbiota as the sole factor contributing to the adaptive physiology of a vertebrate using a unique study design. These findings provide novel insights into the key role of gut microbial symbionts in increasing the invasive potential of its vertebrate host.

O_LISeasonal migration in birds involves a substantial spatial redistribution of avian biodiversity each year and drives seasonal changes in community composition. Migrants experience different combinations of species interactions over space and time, generating regular disassembly and reassembly of bird communities throughout their annual cycles. However, the effects of seasonal migration on phylogenetic community structure remain poorly understood. C_LIO_LIWe assess spatiotemporal variation in phylogenetic community structure of North American passerines to test how seasonal migration restructures the evolutionary relatedness and dominant assembly mechanisms in bird communities throughout the annual cycle. Using distributional projections, we calculated metrics describing the phylogenetic dispersion of passerine communities each week of the year. We then tested the relationship between seasonal turnover in community phylogenetic dispersion and seasonal variation in species richness and proportion of migratory species. C_LIO_LISeasonal migration, by changing spatial patterns of avian diversity, simultaneously drives a complex continental redistribution of phylogenetic community structure. We find evidence of taxonomic scale dependency to our results, wherein throughout North America, the seasonal influx of migrant passerines yields communities that are overall more phylogenetically clustered, yet also exhibit greater phylogenetic overdispersion at smaller taxonomic scales. C_LIO_LISeasonal shifts in phylogenetic dispersion, though complex, track changes in diversity, manifesting as fluctuations in phylogenetic dispersion between northern and southern regions as seasonal migrants move between these regions. Our findings reveal a dynamic continental landscape of phylogenetic community structure directed by the movements of seasonal migrants. C_LI

O_LIEvents such as anthropogenic activities and periodic tree masting can alter resource provisioning in the environment, directly affecting animals, and potentially impacting the spread of infectious diseases in wildlife. The effect of these supplemental resources on infectious diseases can manifest through different pathways, affecting host susceptibility, transmission and host demography. C_LIO_LITo date however, empirical research has tended to examine these different pathways in isolation, for example by quantifying the effects of provisioning on host behaviour in the wild or changes in immune responses in controlled laboratory studies. Further, while theory has investigated the interactions between these pathways, thus far this work has focussed on a narrow subset of pathogen types, typically directly-transmitted microparasites. Given the diverse ways that provisioning can affect host susceptibility, contact patterns or host demography, we may expect the epidemiological consequences of provisioning to depend on key aspects of parasite life-history, such as the duration of infection and transmission mode. C_LIO_LIWe developed a suite of generic epidemiological models to compare how resource provisioning alters responses for different parasites that vary in their biology (micro- and macro-parasite), transmission mode (direct, environmental, and vector transmitted) and duration of infection (acute, latent, and chronic). Next, we parameterised these different parasite types using data from the diverse parasite community of wild wood mice as a case study. C_LIO_LIWe show there are common epidemiological responses to host resource provisioning across all parasite types examined. In particular, the response to provisioning could be driven in opposite directions, depending on which host pathways (contact rate, susceptibility or host demography) are most altered by the addition of resources to the environment. Broadly, these responses were qualitatively consistent across all parasite types, emphasising the importance of identifying general trade-offs between provisioning-altered parameters. C_LIO_LIDespite the qualitative consistency in responses to provisioning across parasite types, we found notable quantitative differences between parasites, suggesting specific epidemiological outcomes could strongly depend on parasite type, infection duration and permanency of recovery, and whether the parasite is directly, environmentally, or vector transmitted. These analyses therefore highlight the importance of knowing key specific aspects of host-parasite biology, such as host contact behaviours, parasite interactions with the host immune system, and how resource availability shapes host demographics, in order to understand and predict epidemiological responses to provisioning for any specific host-parasite system. C_LI

Parental care can shape post-fledging behaviour through provisioning, guidance and social information, yet its absence may alter how young birds establish space use and habitat preferences. We tested the consequences of absent parental care by comparing, hand-reared juvenile herring gulls released without parents with wild, parent-reared conspecifics, focusing on the first two months after fledging. Wild juveniles frequently revisited their natal nest during the first month, whereas hand-reared birds rarely returned to the release site; revisits declined in both groups by the second month but remained more common in wild birds. Wild juveniles used smaller ranges that subsequently expanded, while hand-reared birds began with larger ranges that later contracted, leading to convergence. Contrary to expectation, wild juveniles occurred in areas with higher human population density than hand-reared birds. Habitat use also differed between groups and changed over time. Early on, wild juveniles concentrated activity in anthropogenic and marine habitats, whereas hand-reared birds used rural green habitats more. Later, both groups shifted away from marine areas towards rural green habitats, reducing but not eliminating between-group differences. Short-term survival, did not differ between hand-reared and wild juveniles, indicating that parental care primarily reshaped early space use and habitat choice rather than immediate survival.

Vertebrate gut microbiome has significant effects on host development, health, and fitness. Multiple external factors contribute to gut microbiome variation, and the role of ambient temperature has gained increasing attention. Yet, temperature effects are often tested in extremes and in captive systems. We experimentally studied the effect of subtle temperature decreases during post-natal development on gut microbiome diversity and composition in wild pied flycatchers (Ficedula hypoleuca). We also performed partial cross-fostering to study the relative contribution of genetic and rearing environment on microbiome. Nest-box cold treatment did not influence gut microbiome diversity or composition, which may be due to the small temperature change, ontogenetic stage, or other factors, such as diet, causing large variation in the data. Rearing environment explained more of the variation in gut microbiome than genetic background, but the variance explained was relatively small. Future studies need to further address the drivers of the large intraspecific variation in microbiome in natural populations.

Bat populations experience inter-annual variation in demographic rates in response to environmental conditions. This variation has the potential to impact population sizes and structures, in addition to population-level processes such as disease spread. To establish the influence of variation in demography on these processes, we develop a spatial, individual based model of a serotine bat (Eptesicus serotinus) population, within which we introduce a synthetic lyssavirus-like disease. Model results show that increasing demographic variation, particularly in survival rates, may drive substantial population decline in bat populations. Increasing environmental fluctuations driven by climate change may therefore be problematic for population persistence. The likelihood of disease persistence was also reduced by increasing variation. These findings highlight the limitations of only considering mean demographic rates for prediction of population size change and disease dynamics from models.

Host life-history traits can influence host-vector encounter rates, and so differentially determine the exposure risk of bird species. This modulation of host-virus encounters dynamics is especially important when facing "generalist" arboviruses like West Nile virus (WNV) and Saint Louis Encephalitis virus (SLEV). Using prevalence data collected by our laboratory since 2004, we tested several hypothesis that included birds ecological and life-history traits to determine which traits were better predictors of birds exposure risk to these arboviruses. By means of information-theoretic procedures and generalized mixed linear models, we observed that body mass was an important trait when predicting birds exposure risk to WNV and SLEV and migratory status significantly influenced birds exposure risk only to WNV. Our study highlights important traits to consider when studying the transmission system of these arboviruses, being useful to focus resources when characterizing viral transmission networks and discuss the repercussions of these traits over birds immune function throughout the pace of life syndrome and trade-offs theory.

Animal personality and parasite infections are key forces shaping the ecology and evolution of natural populations. Personality traits--such as activity, exploration, and boldness--shape how individuals interact with their environment and conspecifics, influencing both their exposure and susceptibility to parasite infection. In turn, parasites can impact host fitness and energy allocation, and may modify host behaviour either through manipulations to enhance transmission or as consequences of energetic trade-offs associated with mounting an immune response. Despite growing interest in the interplay between behaviour and infection, the overall directionality and consistency of personality-parasite relationships remain unclear. This relationship is further modulated by ecological and biological factors, such as parasite type (e.g. micro-, ecto-, or endoparasites) and host type (e.g. intermediate versus definitive), which can influence both infection risk and the nature of behavioural responses. To disentangle these effects, we performed a meta-analysis of 226 effect sizes across 80 studies, assessing (i) the impact of experimental infections on host personality traits, and (ii) the correlation between personality and infection status in observational studies of wild populations--while accounting for variation in parasite groups and host roles. In experimental studies, infected hosts exhibited significantly reduced levels of activity and exploration, while effects on boldness and aggressiveness were non-significant. These findings suggest that infection imposes energetic costs that suppress behaviours requiring sustained effort, such as movement and exploration. Conversely, observational studies showed a positive association between activity-exploration and infection probability, likely reflecting greater exposure of more active individuals to parasites via increased interaction with conspecifics or contaminated environments. Meta-regression analyses further revealed that parasite type and host role modulate personality-infection dynamics. In experimental studies, microparasites were associated with reduced boldness and activity-exploration, while endoparasites led to reduced activity- exploration--particularly in intermediate hosts. Notably, hosts showed significant behavioural suppression in experimental contexts, but not in observational studies, potentially indicating that behaviourally tolerant individuals are favoured in natural environments where personality traits relate directly to fitness. Together, these findings underscore the importance of ecological context and study design in interpreting personality-parasite associations. Experimental infections tend to reveal the physiological costs of infection, while observational studies highlight behavioural traits that modulate infection risk. By integrating data across host types, parasite groups, and methodological approaches, our meta-analysis provides a more comprehensive understanding of how personality and infection interact. These insights contribute to a broader effort to link behavioural ecology with disease ecology, clarifying how individual variation in behaviour shapes--and is shaped by--host-parasite dynamics.

O_LIHow early-life exploration shapes the adult annual cycle routines of migratory animals remains challenging to study, especially in long-lived species. Delayed recruitment often observed in long-lived migratory birds suggests that the first breeding attempt may be constrained by a protracted learning process in which individuals develop their annual itinerary, which may involve extensive exploration of the winter and breeding sites, potentially causing inexperienced young to wander beyond traditional population areas. C_LIO_LIUsing greater flamingo Phoenicopterus roseus GPS tracking data from 83 individuals tagged as nestlings in the Mediterranean, we analyzed ontogenetic changes in mobility and space use for up to 8 years of age. We segmented autumn-winter and spring-summer tracks (n = 223 device-bird-year combinations) into staging events (n = 1914). We then computed seasonal staging metrics and analysed how they changed with age. We map the traditional congregation sites of flamingos to investigate age-related changes in space use between males and females. C_LIO_LIFlamingos were more exploratory during their early years, gradually transitioning to a more sedentary lifestyle as they grew older. With each additional year of age, the number of staging events decreased by 16%, while the average duration of staging events increased by 8 days. C_LIO_LIBirds remained faithful to the non-breeding staging sites where they spent most of their time during the first year of life. Over time, they returned progressively closer to their natal sites, even after years of exploration at non-traditional locations. Breeding was rare (8%) and occurred at a relatively late age ([≥]5 years), highlighting an extended exploratory phase, a pattern observed in other long-lived species. C_LIO_LIOlder birds were more likely to use traditional sites and spent more time at these sites, particularly after age 5. Our study reveals the individual exploration process underlying natal and non-breeding dispersal patterns previously laid bare by ring-resighting studies and shows that flamingos retain long-term memory of sites learned in early life. C_LI

Sleep is a highly complex and conserved biological process that affects several body functions and behaviors. Recent evidence suggests that there is a reciprocal interaction between sleep and immunity. For instance, fragmented sleep can increase the probability of parasitic infections and reduce the ability of infected hosts to fight infections. It is also known, particularly in humans and other mammals, that viral and bacterial infections alter the sleep patterns of infected individuals. However, the effects of macro-parasitic infections on sleep remain largely unknown. In this study, we investigated whether macro-parasite infections could alter the sleep of their hosts. We experimentally infected three-spined sticklebacks (Gasterosteus aculeatus) with the tapeworm Schistocephalus solidus and used a hidden Markov model to characterize sleep-associated behaviors in the sticklebacks. At an early time-point, 1-4 days after parasite exposure, infected fish showed no difference in sleep compared with non-exposed fish, whereas fish that were exposed but could fend off the infection slept less during the daytime. At a later time-point, 29-32 days after exposure, infected fish slept more than uninfected fish, while exposed-but-not-infected fish slept less than non-exposed fish. Using RNA-seq of brain tissue, we identified several immune- and sleep-associated genes that potentially underlie the observed behavioral changes. These results provide the first insight into the complex association between macro-parasite infection, immunity, and sleep in fish and may thus contribute to a better understanding of the reciprocal interaction between sleep and immunity.