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Characterizing spatial differences in wildlife immunity is the first step to identify environmental drivers of host defense and disease risks. The house sparrow (Passer domesticus) is a model system for ecoimmunology, but spatial differences in immunity have been largely restricted to the invasive range of this global species. We provide an initial test of spatial variation in immune response to phytohemagglutinin in the native range, finding that birds from Romania have greater inflammatory responses than birds from Egypt. Future broad surveys across the house sparrow native range could contextualize these differences and determine underlying drivers. [ABSTRACT FROM AUTHOR]

The variability of intrinsic and extrinsic factors to which wild populations are exposed may have consequences for the immune response, and hence, the host's susceptibility to parasite infection may be affected. The present study aimed at evaluating the relationship between markers of anti- and pro-inflammatory immune responses and individual characteristics (age, sex, body condition), parasite parameters and seasonality in the mouse Akodon azarae (Cricetidae: Sigmodontinae). Expression levels of anti-inflammatory (IL-10 and TGF-β) and pro-inflammatory (TNF-α) cytokines in wild rodents were determined using real-time reverse transcription-polymerase chain reaction. The associations of each anti-inflammatory cytokine with endo- and ectoparasites depended on individual variables and seasonality. TGF-β was associated with endoparasites and body condition, while IL-10 was associated with ectoparasites. TNF-α showed a positive association with ectoparasites, which tended to be reversed when endoparasite abundance was high. In addition, levels of this cytokine tended to decrease with ectoparasite richness in autumn. Overall, we found that the association between ectoparasites and pro-inflammatory markers depended on season and endoparasite abundance, while its association with anti-inflammatory responses depended on both age and season. For each cytokine evaluated, there may be different factors that influence the results of mice-parasite interaction, such as co-infections, seasonality and host factors (e.g., age, sex, body condition). The information generated by this study is relevant to better understand infection dynamics and host-parasite interactions in wild rodents of this group. [ABSTRACT FROM AUTHOR]

Non-native species invasions are increasing across the globe and are affecting native species in many different ways including through impacts as novel predators or food sources. We sought to understand how eastern fence lizards (Sceloporus undulatus) are affected by invasive red imported fire ants (Solenopsis invicta), which serve as both predator and prey to the lizards. These ants have been present in the lizards' range for over 70 years and are associated with altered lizard immune function as compared to lizards from ecologically similar sites not invaded by fire ants. To better assign causation to the correlative field patterns of immune function, we experimentally exposed fire ant-naïve lizards to fire ant venom though ant stings and via consumption of non-stinging dead ants and measured the same immune outcomes. Fire ant consumption increased lizard immune responses relative to lizards stung by fire ants, and two of the four immune differences in the field were also seen in lizards fed fire ants (higher anti-fire ant IgM and basophils). This may indicate that some field-measured immune differences in fire ant invaded populations of lizards are directly due to their exposure to fire ant venom by consuming fire ants rather than through stinging. These results also suggest that consumption of fire ants can bolster immune responses needed to combat envenomation through stinging. This adds to growing evidence that sub-lethal consumption of poisonous/venomous invasive species may reduce deleterious consequences of exposure to these toxins, allowing native species to survive and coexist with otherwise deadly invaders. [ABSTRACT FROM AUTHOR]

As environmental changes exacerbate the threat coming from infectious diseases in wild mammal species, monitoring their health and gaining a better understanding of the immune functioning at the species level have become critically important. Neopterin is a biomarker of cell-mediated immune responses to intracellular infections. We investigated the variation of urinary neopterin (uNeo) levels of wild, habituated bonobos (Pan paniscus) in relation to individual and environmental factors. We used 309 urine samples collected between 2010 and 2018 at the LuiKotale field site, DRC. Based on current knowledge on zoo-housed conspecifics and closely related species, we predicted uNeo levels to increase (1) during infections, (2) with increasing age, (3) over the gestation period and in estrous females; and (4) to vary seasonally. Our results showed uNeo levels varied over a one-year period and increased in individuals showing respiratory symptoms. Contrary to chimpanzees, uNeo levels did not vary with age or female reproductive status, possibly due to our small sample size. Our study provides a baseline for a better understanding of bonobo's immunocompetence in the context of socio-ecological pressures and for monitoring the health of wild populations. [ABSTRACT FROM AUTHOR]

How hosts respond to and cope with infectious agents can change the environment and in so doing, alter selective pressures and evolutionary trajectories. To date, such eco-evolutionary feedbacks are best known from simplified mathematical models and laboratory experiments with a limited number of genetically homogenous model systems. However, the extent to which ecology and (co)-evolution interact to shape disease over space and time in natural communities remains poorly understood. Studies in this theme issue break new ground by integrating empirical and field studies stemming from a diverse array of taxa and ecosystems to understand how ecological and evolutionary feedbacks shape host-parasite interactions. Contributing papers synthesize emerging research and diverse perspectives on pathogen life history, virulence, resistance, leveraging novel methodological advances and integrating infection processes across multiple scales of biological organization. Two key take-aways emerge from this theme issue. First, more research tackling the eco-evolutionary dynamics of infectious disease in truly multi-species contexts is needed. Second, while we are far from understanding eco-evolutionary dynamics in the 'natural theater' where hosts encounter their parasites, exciting advances and foundational studies provide a well-defined road map. [ABSTRACT FROM AUTHOR]

What are the relative costs and benefits of mounting immune responses? Practitioners of ecoimmunology have grappled with this central question since the field's inception with the main tension being how to make tractable methodological choices that maintain the ecological relevance of induced and measured immune costs. Here, we point out two methodological approaches that we feel are underrepresented in the field, describe risks associated with neglecting these methods, and suggest modern techniques that maximize both the diversity and ecological relevance of collected data. First, it is commonly assumed that frequently used and experimentally convenient immune stimulants will induce ecologically relevant immune responses in study organisms. This can be a dangerous assumption. Even if a stimulant's general immune response properties are well characterized, it is critical to also measure the type and scale of immune responses induced by live pathogens. Second, patterns of immune defenses evolve like other traits, thus a comparative approach is essential to understand what forces shape immune variation. Finally, we describe modern genetic and immunological approaches that will soon become essential tools for ecoimmunologists, and present case studies that exemplify the utility of our recommendations. [ABSTRACT FROM AUTHOR]

Mining is one of the main activities that drive the economy of Brazil. Mining activity is associated with risk of contamination of environment and local fauna by metals. Amphibians have a life cycle that requires a transition between aquatic and terrestrial environments, increasing their vulnerability to metal contamination in the water and substrate. Metals are ubiquitous, with high bioaccumulative and biomagnifying potential, and may lead to immune and endocrine disruption. In this study, we analyzed two different components of the innate immune response, bacterial killing ability (BKA) and phytohemagglutinin edema (PHA), and two stress biomarkers, corticosterone plasma levels (CORT) and the neutrophil to lymphocyte ratio (N:L), of toads (Rhinella diptycha) living in places contaminated by metals. Blood samples were collected pre- and post-restraint (1h), followed by an immune challenge with PHA and tissue collection (liver, spleen, and kidneys). Toads liver metal bioaccumulation did not correlate with the immune response or stress biomarkers. Post-restraint, animals had increased CORT and reduced BKA, independently of the collection site, and these variables were not correlated with liver metal bioaccumulation. Interestingly, toads with the larger spleen (immune organ) showed increased N:L post-restraint and greater edema after the PHA challenge. Our results indicate that toads living in metal-contaminated environments responded to acute stressor, activating the hypothalamic-pituitary-interrenal axis and the immune response. Keep tracking the physiological variables of these animals and the presence of metals in the environment and tissues should provide valuable health status indicators for the population, which is vital for proposing amphibian conservation strategies in these areas. [ABSTRACT FROM AUTHOR]

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When animals are faced with a life-threatening challenge, they mount an organism-wide response (i.e. Plan A). For example, both the stress response (i.e. fight-or-flight) and the immune response recruit molecular resources from other body tissues, and induce physiological changes that optimize the body for defense. However, pathogens and predators often co-occur. Animals that can optimize responses for a dual challenge, i.e. simultaneous predator and pathogen attacks, will have a selective advantage. Responses to a combined predator and pathogen attack have not been well studied, but this paper summarizes the existing literature in insects. The response to dual challenges (i.e. Plan B) results in a suite of physiological changes that are different from either the stress response or the immune response, and is not a simple summation of the two. It is also not a straight-forward trade-off of one response against the other. The response to a dual challenge (i.e. Plan B) appears to resolve physiological trade-offs between the stress and immune responses, and reconfigures both responses to provide the best overall defense. However, the dual response appears to be more costly than either response occurring singly, resulting in greater damage from oxidative stress, reduced growth rate, and increased mortality. [ABSTRACT FROM AUTHOR]

Billions of animals migrate between breeding and non-breeding areas worldwide. Partial migration, where both migrants and residents coexist within a population, occurs in most animal taxa, including fish, insects, birds and mammals. Partial migration has been hypothesised to be the most common form of migration and to be an evolutionary precursor to full migration. Despite extensive theoretical models about partial migration and its potential to provide insight into the ecology and evolution of migration, the physiological mechanisms that shape partial migration remain poorly understood. Here, we review current knowledge on how physiological processes mediate the causes and consequences of avian partial migration, and how they may help us understand why some individuals migrate and others remain resident. When information from birds is missing, we highlight examples from other taxa. In particular, we focus on temperature regulation, metabolic rate, immune function, oxidative stress, telomeres, and neuroendocrine and endocrine systems. We argue that these traits provide physiological pathways that regulate the ecological and behavioural causes and/or consequences of partial migration, and may provide insight into the mechanistic basis of wintering decisions. They may, thus, also help us to explain why individuals switch strategies among winters. We also highlight current gaps in our knowledge and suggest promising future research opportunities. A deeper understanding of the physiological mechanisms mediating the causes and consequences of partial migration will not only provide novel insights into the ecology and evolution of migration in general, but will also be vital to precisely modelling population trends and predicting range shifts under global change. [ABSTRACT FROM AUTHOR]

Life-history trade-offs result from allocation of limited energetic resources to particular traits at the expense of others. When resources are scarce, some traits will take priority over others in the degree of their expression. For example, the current reproduction may be sacrificed to enhance survival. Although intuitive from an evolutionary perspective, such priorities must be based on proximate mechanisms that respond to the current conditions. The hormone leptin serves as a signal of energy availability in vertebrates, and has been proposed as a mediator of energy allocation between reproduction and traits that enhance survival, such as the immune system. However, since leptin affects reproduction and immunity in a similar way, it remains unclear which takes priority when energy availability is low. Green anole lizards (Anolis carolinensis) with increased activity, via exercise training, have a marked decrease in immune function as well as reproduction, especially when calories are restricted. We hypothesized that endurance training and calorie restriction would lower immune and reproductive function due to energy limitation, and supplemental leptin would 'rescue' either immune function or reproduction (or both) due to the hormonal signal that energetic resources are available. We found that supplementary leptin rescued immune function in calorie-restricted, trained lizards, but reproduction was not rescued in males or females. This suggests that immune function and reproduction have different sensitivities to leptin in both sexes, or that reproduction is more energy limited and takes low priority even when the signal of energy availability is present. [ABSTRACT FROM AUTHOR]

The relationships between immunity, oxidative stress, and diet have not often been studied together. Despite this, it has been shown that dietary proteins can have effects on the functioning of the immune system and the oxidative status of animals. Here we evaluated the effects of dietary proteins on the response to an antigen and oxidative status of Octodon degus (Rodentia). We acclimated adult individuals to high-protein and low-protein diets and evaluated several aspects of the acute phase response and variables associated with oxidative status. After the immune challenge, animals acclimated to the high-protein diet had more inflammatory proteins and body mass losses than the group acclimated to a low-protein diet. Overall, the immune challenge increased the production of inflammatory proteins, total antioxidant capacity, lipid peroxidation, and duration of rest periods. In contrast, we did not find an interaction between diet and the challenge with the antigen. Overall, our results do not reveal an enhanced response to an antigen nor effects on the oxidative status of degus individuals subjected to a high-protein diet. [ABSTRACT FROM AUTHOR]

Many fishes express high levels of intraspecific variability, often linked to resource partitioning. Several studies show that a species' evolutionary trajectory of adaptive divergence can undergo reversals caused by changes in its environment. Such a reversal in neutral genetic and morphological variation among lake trout Salvelinus namaycush ecomorphs appears to be underway in Lake Superior. However, a water depth gradient in neutral genetic divergence was found to be associated with intraspecific diversity in the lake. To investigate patterns of adaptive immunogenetic variation among lake trout ecomorphs, we used Illumina high-throughput sequencing. The population's genetic structure of the major histocompatibility complex (MHC Class IIβ exon 2) and 18 microsatellite loci were compared to disentangle neutral and selective processes at a small geographic scale. Both MHC and microsatellite variation were partitioned more by water depth stratum than by ecomorph. Several metrics showed strong clustering by water depth in MHC alleles, but not microsatellites. We report a 75% increase in the number of MHC alleles shared between the predominant shallow and deep water ecomorphs since a previous lake trout MHC study at the same locale ( c. 1990s data). This result is consistent with the reverse speciation hypothesis, although adaptive MHC polymorphisms persist along an ecological gradient. Finally, results suggested that the lake trout have multiple copies of the MHC II locus consistent with a historic genomic duplication event. Our findings indicated that conservation approaches for this species could focus on managing various ecological habitats by depth, in addition to regulating the fisheries specific to ecomorphs. [ABSTRACT FROM AUTHOR]

Resource availability can significantly alter host-parasite dynamics. Abundant food can provide more resources for hosts to resist infections, but also increase host tolerance of infections by reducing competition between hosts and parasites for food. Whether abundant food favors host resistance or tolerance (or both) might depend on the type of resource that the parasite exploits (e.g., host tissue vs. food), which can vary based on the stage of infection. In our study, we evaluated how low and high resource diets affect Cuban tree frog ( Osteopilus septentrionalis) resistance and tolerance of a skin-penetrating, gut nematode Aplectana sp. at each stage of the infection. Compared to a low resource diet, a high resource diet enhanced frog resistance to worm penetration and tolerance while worms traveled to the gut. In contrast, a low resource diet increased resistance to establishment of the infection. After the infection established and worms could access food resources in the gut, a high resource diet enhanced host tolerance of parasites. On a high resource diet, parasitized frogs consumed significantly more food than non-parasitized frogs; when food was then restricted, mass of non-parasitized frogs did not change, whereas mass of parasitized frogs decreased significantly. Thus, a high resource diet increased frog tolerance of established worms because frogs could fully compensate for energy lost to the parasites. Our study shows that host-parasite dynamics are influenced by the effect of resource availability on host resistance and tolerance, which depends on when parasites have access to food and the stage of infection. [ABSTRACT FROM AUTHOR]

Local adaptation may optimize an organism's investment in defenses in response to the risk of infection by spatially heterogeneous parasites and other natural enemies. However, local adaptation may be constrained if recruitment is decoupled from selective pressure experienced by the parent generation. We predicted that the ability of three intertidal littorinid snail species to defend against trematode parasites would depend on prior levels of population exposure to parasites and on larval dispersal mode, a proxy for population openness. In a common garden experiment, for two snail species with direct development and localized recruitment ( Littorina obtusata and Littorina saxatilis), hosts from sites with high trematode infection risk were less susceptible to infection than hosts from low-risk sites. However, this relationship was not apparent for a third host species with broadcast larvae ( Littorina littorea), suggesting that broad larval dispersal can impede local adaptation; alternatively, the lack of response in this species could owe to other factors that limited experimental infection in this host. Our findings support that locally recruiting hosts can adapt their defenses to scale with localized infection risk. [ABSTRACT FROM AUTHOR]

Understanding the complexity of host immune responses to parasite infection requires controlled experiments that can inform observational field studies. Birds and their malaria parasites provide a useful model for understanding host-parasite relationships, but this model lacks a well-described experimental context for how hosts respond immunologically to infection. Here, ten canaries ( Serinus canaria) were infected with the avian malaria parasite Plasmodium relictum (lineage SGS1) in a controlled laboratory setting with ten uninfected (control) birds. A suite of immunological blood parameters, including the concentration of four white blood cell types, the concentration of the acute phase protein haptoglobin, and the bacteria-killing ability of blood plasma, were repeatedly measured over a 25-day period covering the acute phase of a primary infection by P. relictum. Three infected and one control bird died during the course of the experiment. A multivariate statistical analysis of the immune indices revealed significant differences between infected and uninfected individuals between 5 and 14 days postinfection (dpi). Group differences corresponded to reduced concentrations of lymphocytes (5 dpi), heterophils (8 dpi), and monocytes (11 and 14 dpi), and an increase in haptoglobin (14 dpi), in infected birds relative to uninfected controls, and no change in bacteria-killing. Upon re-running the analysis with only the surviving birds, immunological differences between infected and control birds shifted to between 11 and 18 dpi. However, there were no clear correlates relating immune parameters to the likelihood of surviving the infection. The results presented here demonstrate the dynamic and complex nature of avian immune function during the acute phase of malaria infection and provide a context for studies investigating immune function in wild birds. [ABSTRACT FROM AUTHOR]

Energy budgets explain how organisms allocate energetic intake to accomplish essential processes. A likely life history trade-off occurs between growth and immune response in juvenile organisms, where growth is important to avoid predation or obtain larger prey and immune response is essential to survival in the presence of environmental pathogens. We examined the innate (wound healing) and adaptive (lymphoid tissue, thymus and spleen) components of immune response along with growth in two populations of the diamond-backed watersnake Nerodia rhombifer raised in a common environment. We found that neonate snakes born to females from populations characterized by different predator and prey environments did not differ in energetic intake, but snakes from the population containing large prey grew significantly faster than those from a population containing small prey. Thymus mass, when corrected for body mass, was larger in snakes from the small prey population than in snakes from the large prey population. Additionally, the snakes from the population containing small prey healed significantly faster than those from the population containing large prey. Thus, we detected a negative correlation between growth (over a 4-month period) and wound healing across populations that is suggestive of an energetic trade-off between growth and immune response. The differences observed in growth and immune response among these two populations appear to suggest different energy allocation strategies to maximize fitness in response to differing conditions experienced by snakes in the two populations. [ABSTRACT FROM AUTHOR]

Host responses to parasitism in the wild are often studied in the context of single host-parasite systems, which provide little insight into the ecological dynamics of host-parasite interactions within a community. Here we characterized immune system responses to mostly low-intensity, chronic infection by haemosporidian parasites in a sample of 424 individuals of 22 avian host species from the same local assemblage in the Missouri Ozarks. Two types of white blood cells (heterophils and lymphocytes) were elevated in infected individuals across species, as was the acute-phase protein haptoglobin, which is associated with inflammatory immune responses. Linear discriminant analysis indicated that individuals infected by haemosporidians occupied a subset of the overall white blood cell multivariate space that was also occupied by uninfected individuals, suggesting that these latter individuals might have harbored other pathogens or that parasites more readily infect individuals with a specific white blood cell profile. DNA sequence-defined lineages of haemosporidian parasites were sparsely distributed across the assemblage of hosts. In one well-sampled host species, the red-eyed vireo ( Vireo olivaceus), heterophils were significantly elevated in individuals infected with one but not another of two common parasite lineages. Another well-sampled host, the yellow-breasted chat ( Icteria virens), exhibited no differences in immune response to different haemosporidian lineages. Our results indicate that while immune responses to infection may be generalized across host species, parasite-specific immune responses may also occur. [ABSTRACT FROM AUTHOR]

Defense against natural aggressors, such as bacterial infections, requires both energy and an immune-cellular response. However, the question as to how these two components are interconnected in small endotherms by means of the host diet remains only poorly understood. Here, we tested in laboratory mice whether dietary proteins and carbohydrates can modulate the interplay between energy expenditure, food intake and the innate and adaptive immune response when confronting a bacterial challenge (Bacillus Calmette-Guérin, BCG). We observed that mice fed with a high protein diet (HP) developed a better immune response associated to increased numbers of circulating monocytes. In addition, HP diet directly influenced the peripheral blood proportions of both T and B lymphocytes even before the BCG challenge. Interestingly, animals that developed this type of immune response after BCG challenge showed an increased rate of metabolism and food consumption before being challenged. Thus, HP diet induced in non-challenged animals a similar energy expenditure and food intake described by BCG-treated mice. These data suggest that a high amount of proteins in diet can modify the energetic and nutrient dynamic in the host causing a better immune reaction against a microbial challenge. [ABSTRACT FROM AUTHOR]

The endocrine system serves as a mediator by which the body integrates environmental cues to organize physiological alterations, including changes in immunocompetence. Hormones are central mechanisms that contribute to the onset and timing of key life history events, the allocation of time and energy between competing functions, and in general modulate phenotypic development and variation. Here we provide a very brief review of testosterone and immunity, which highlights the physiological costs that elevated testosterone levels can incur as a result of reproductive investments. We focus primarily on nonhuman primates where possible. Although there is substantial evidence that testosterone exerts some influences on immune responses, results from in vivo studies involving human and nonhuman primates have yielded equivocal results regarding such immunomodulatory actions. There may be several reasons for this, including variation in study design, immunological measures used, levels of other hormones present, host energy status, and even social conditions. We therefore review some of these potential methodological issues, concluding that increased care must be taken to analyze seasonal variability in energy budgets, to collect an adequate number of samples from known individuals, to account for status in the dominance hierarchy when applicable, and to use multiple measures of immunity. We must also seek to understand the collaborative effects of multiple hormones (particularly dehydroepiandrosterone and estradiol) with relation to their downstream immunological effects, assessing both individual and multiplicative actions in both males and females. Such efforts would benefit from the development of additional noninvasive immune measures for primates. [ABSTRACT FROM AUTHOR]

Immune system function is affected by a variety of exogenous and endogenous stressors. Most studies have focused on the effect of stressors on immune function, but not necessarily on trade-offs within the immune system and interactions with energy-mobilizing hormones. In this study, we examined how bactericidal ability and corticosterone interacted by applying acute restraint stress in a non-model organism, the side-blotched lizard ( Uta stansburiana), 10 days after receiving a cutaneous wound. We found a decrease in bactericidal ability in wounded animals after restraint stress. However, the percentage healed during the first 7 days was positively correlated with bactericidal ability 10 days after wounding. In addition, the magnitude of change in corticosterone concentration during the acute stress was positively correlated with the percentage of wound healing during the first 3 days. These two relationships may demonstrate a 'faster is better' strategy. If energy is invested heavily in the initial wound healing stages, the individual may be able to mount a more effective immune and stress response earlier. [ABSTRACT FROM AUTHOR]

Reproduction is a notoriously costly phase of life, exposing individuals to injury, infectious disease, and energetic trade-offs. The strength of these costs should be influenced by life history strategies, and in long-lived species, females may be selected to mitigate costs of reproduction because life span is such an important component of their reproductive success. Here, we report evidence for two costs of reproduction that may influence survival in wild female baboons-injury risk and delayed wound healing. Based on 29 years of observations in the Amboseli ecosystem, Kenya, we found that wild female baboons experienced the highest risk of injury on days when they were most likely to be ovulating. In addition, lactating females healed from wounds more slowly than pregnant or cycling females, indicating a possible trade-off between lactation and immune function. We also found variation in injury risk and wound healing with dominance rank and age: Older and low-status females were more likely to be injured than younger or high-status females, and older females exhibited slower healing than younger females. Our results support the idea that wild nonhuman primates experience energetic and immune costs of reproduction and they help illuminate life history trade-offs in long-lived species. [ABSTRACT FROM AUTHOR]

A central hypothesis of eco-immunology proposes trade-offs between immune defences and competing physiological and behavioural processes, leading to immunological variation within and among annual-cycle stages, as has been revealed for some species. However, few studies have simultaneously investigated patterns of multiple immune indices over the entire annual cycle in free-living birds, and none has investigated the consistency of seasonal patterns across multiple years. We quantified lysis, agglutination, haptoglobin, leukocyte profiles, and body mass in free-living skylarks ( Alauda arvensis) through two complete annual cycles and within and between four breeding seasons. The skylarks' annual cycle is characterised by annually repeated changes in energy and time budgets, social structure and diet. If trade-offs relating to these cyclic changes shape evolution, predictable intra-annual immune patterns may result. Alternatively, intra-annual immune patterns may vary among years if fluctuating environmental changes affect the cost-benefit balances of immune function. We found significant variation in immune indices and body mass across the annual cycle, and these patterns differed between years. Immune parameters differed between four breeding seasons, and in all years, lysis and agglutination increased as the season progressed independent of average levels. Population-level patterns (intra-annual, inter-annual, within breeding season) were consistent with within-individual patterns based on repeated measurements. We found little evidence for sex differences, and only haptoglobin was correlated (negatively) with body mass. We conclude that immune modulation is not simply a pre-programmed phenomenon that reflects predictable ecological changes. Instead, fluctuating environmental conditions that vary among years likely contribute to the immunological variation that we observed. [ABSTRACT FROM AUTHOR]

Numerous environmental chemicals, both long-known toxicants such as persistent organic pollutants as well as emerging contaminants such as pharmaceuticals, are known to modulate immune parameters of wildlife species, what can have adverse consequences for the fitness of individuals including their capability to resist pathogen infections. Despite frequent field observations of impaired immunocompetence and increased disease incidence in contaminant-exposed wildlife populations, the potential relevance of immunotoxic effects for the ecological impact of chemicals is rarely considered in ecotoxicological risk assessment. A limiting factor in the assessment of immunotoxic effects might be the complexity of the immune system what makes it difficult (1) to select appropriate exposure and effect parameters out of the many immune parameters which could be measured, and (2) to evaluate the significance of the selected parameters for the overall fitness and immunocompetence of the organism. Here, we present - on the example of teleost fishes - a brief discussion of how to assess chemical impact on the immune system using parameters at different levels of complexity and integration: immune mediators, humoral immune effectors, cellular immune defenses, macroscopical and microscopical responses of lymphoid tissues and organs, and host resistance to pathogens. Importantly, adverse effects of chemicals on immunocompetence may be detectable only after immune system activation, e.g., after pathogen challenge, but not in the resting immune system of non-infected fish. Current limitations to further development and implementation of immunotoxicity assays and parameters in ecotoxicological risk assessment are not primarily due to technological constraints, but are related from insufficient knowledge of (1) possible modes of action in the immune system, (2) the importance of intra- and inter-species immune system variability for the response against chemical stressors, and (3) deficits in conceptual and mechanistic assessment of combination effects of chemicals and pathogens. [ABSTRACT FROM AUTHOR]

As the number of invasive species increases globally, more and more native predators are reported to shift their diet toward invasive prey. The consequences of such diet shifts for the health of populations of native predators are poorly studied, but diet shifts are expected to have important parasitological and immunological consequences, ultimately affecting predator fitness. We reviewed evidence that diet shifts from native to invasive prey can alter parasite exposure directly and also indirectly affect immune functions via changes in condition and contaminant exposure. We highlight relevant conceptual and methodological tools that should be used for the design of experiments aimed at exploring important links between invasive prey and parasitism, contaminants and fitness of their native predators. [ABSTRACT FROM AUTHOR]

Immunologists and evolutionary biologists are interested in how the immune system evolves to fit an ecological niche. We studied the relationship between exposure to parasites and strength of immunity by investigating the response of two species of New World cowbirds (genus Molothrus, Icteridae), obligate brood parasites with contrasting life history strategies, to experimental arboviral infection. The South American shiny cowbird ( M. bonariensis) is an extreme host- generalist that lays its eggs in the nests of >225 different avian species. The Central American bronzed cowbird ( M. aeneus) is a relative host- specialist that lays its eggs preferentially in the nests of approximately 12 orioles in a single sister genus. West Nile virus provided a strong challenge and delineated immune differences between these species. The extreme host-generalist shiny cowbird, like the North American host-generalist, the brown-headed cowbird, showed significantly lower viremia to three arboviruses than related icterid species that were not brood parasites. The bronzed cowbird showed intermediate viremia. These findings support the interpretation that repeated exposure to a high diversity of parasites favors the evolution of enhanced immunity in brood parasitic cowbirds and makes them useful models for future studies of innate immunity. [ABSTRACT FROM AUTHOR]