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Urbanization processes modulate the immunological challenges faced by animals. Urban habitat transformations reshape pathogen diversity and abundance, while high population density—common in urban exploiter species—promotes disease transmission. Responses to urbanization may include adaptive adjustments of constitutive innate immune defenses (e.g. complement system and natural antibodies [NAbs]), which serve as first‐line protection against infections. Here, we investigated associations of habitat urbanization and host population density with complement and NAbs in an urban bird, the feral pigeon Columba livia domestica. To do so, we employed the hemolysis–hemagglutination assay to analyze nearly 200 plasma samples collected across urbanization and pigeon population density gradients in five major cities in Poland. We found a negative association between urbanization score and hemagglutination (i.e. NAbs activity), but not hemolysis (i.e. complement activity), indicating either immunosuppression or adaptive downregulation of this immune defense in highly transformed urban landscape. Population density was not significantly related to either immune parameter, providing no evidence for density‐dependent modulation of immune defenses. At the same time, there was a negative association of hemolysis with condition (scaled mass index), suggesting resource allocation trade‐offs or contrasting effects of the urban environment on immune defenses and body condition. The results demonstrate that habitat structure can be an important factor shaping the immune defenses of the feral pigeon, although these associations were not mediated by variation in population density. Our study highlights the complexity of the links between immune defenses in wildlife and urbanization and reinforces the need for comprehensive ecoimmunological studies on urban animals. [ABSTRACT FROM AUTHOR]

Since the discovery of specific immune memory in invertebrates, researchers have investigated its immune response to diverse microbial and environmental stimuli. Nevertheless, the extent of the immune system’s interaction with metabolism, remains relatively enigmatic. In this mini review, we propose a comprehensive investigation into the intricate interplay between metabolism and specific immune memory. Our hypothesis is that cellular endocycles and epigenetic modifications play pivotal roles in shaping this relationship. Furthermore, we underscore the importance of the crosstalk between metabolism and specific immune memory for understanding the evolutionary costs. By evaluating these costs, we can gain deeper insights into the adaptive strategies employed by invertebrates in response to pathogenic challenges. Lastly, we outline future research directions aimed at unraveling the crosstalk between metabolism and specific immune memory. These avenues of inquiry promise to illuminate fundamental principles governing host-pathogen interactions and evolutionary trade-offs, thus advancing our understanding of invertebrate immunology. [ABSTRACT FROM AUTHOR]

Bighorn sheep (Ovis canadensis) are herbivorous ungulates that live in forage-poor areas of the American west. The trace minerals that herbivores derive from forage are important for immune function. Therefore, identifying trace minerals that affect immune function in bighorn sheep could provide important insights into disease susceptibility and population health in threatened populations. We sought to determine whether trace mineral composition in blood or plasma correlates to survival and determine whether immunologic parameters correlate with any trace minerals that affect survival. We used data collected from 2016 to 2018 as part of a large study on bighorn sheep in southeastern Oregon and northern Nevada, US. We measured the survival of 135 bighorn sheep during the 8-mo monitoring period, including general metrics of immune function and trace mineral levels. We found that animals with higher selenium had improved survival over the monitoring period, with higher peripheral blood mononuclear cell activity (lymphocytes and monocytes) and lower bacterial killing ability in an in vitro assay. This suggests that bighorn sheep may have altered immune function when selenium levels are low, making them more likely to die during the 8-mo monitoring period. Future work should consider whether habitat management strategies that increase selenium intake might improve disease resistance and survival in bighorn sheep in selenium-poor areas. [ABSTRACT FROM AUTHOR]

It is well known that hormones influence and direct most facets of physiology; however, there is still contention regarding the directions of certain relationships, for example, between gonadal hormones and immunity. Among the many proposed relationships relating to gonadal–immune interactions, support for immunosuppressive effects of androgens remains prominent within physiological literature. Although ample study has been directed toward the immunosuppressive effects of androgens, considerable disagreement remains regarding their influence on immune function. In this study, we test the hypothesis that androgens inhibit immunocompetence in the American alligator (Alligator mississippiensis). Developing alligators were incubated at female‐producing temperatures with a subset of individuals being exposed to 17‐α‐methyltestosterone (MT) before sexual determination. 17‐α‐methyltestosterone is a potent androgen, not aromatizable by crocodilians, that has been found to exert masculinizing effects in exposed crocodilian populations in vivo and in vitro. Additionally, a subset of animals was exposed to a novel antigen to quantify innate and acquired immune function. We recovered no significant differences in leukocyte ratios or proportions between groups and found no significant differences in innate immune function as measured by hemolysis‐hemagglutination. However, we did find significant differences in acquired immune function, where masculinized individuals expressed greater antibody titers. Our findings reject the hypothesis that androgens suppress immune function; rather, androgens may be immunoenhancing to acquired humoral responses and neutral to innate humoral immunity in crocodilians. [ABSTRACT FROM AUTHOR]

Simple Summary: This commentary focuses on experimental techniques used by researchers to understand how the immune system of an animal can acclimate, or change, to function across different body temperatures. I categorized studies as using three different, broad techniques: (1) allowing animal body temperatures to change naturally; (2) manipulating body temperatures of live animals in a controlled environment; and (3) manipulating temperatures of immune components (plasma, cells, etc.) in laboratory assays. I reviewed how the current literature used these techniques, with the conclusion that combinations of the three different techniques increased a mechanistic understanding of acclimation. In particular, cell-based techniques seem under-utilized and can lead to a greater understanding of how an animal may be changing the numbers of cells in their bodies or changing the cells themselves to function across different temperatures. This short review focuses on current experimental designs to quantify immune acclimation in animals. Especially in the face of rapidly changing thermal regimes, thermal acclimation of immune function has the potential to impact host–pathogen relationships and the fitness of hosts. While much of the field of ecoimmunology has focused on vertebrates and insects, broad interest in how animals can acclimate to temperatures spans taxa. The literature shows a recent increase in thermal acclimation studies in the past six years. I categorized studies as focusing on (1) natural thermal variation in the environment (e.g., seasonal), (2) in vivo manipulation of animals in captive conditions, and (3) in vitro assays using biological samples taken from wild or captive animals. I detail the strengths and weaknesses of these approaches, with an emphasis on mechanisms of acclimation at different levels of organization (organismal and cellular). These two mechanisms are not mutually exclusive, and a greater combination of the three techniques listed above will increase our knowledge of the diversity of mechanisms used by animals to acclimate to changing thermal regimes. Finally, I suggest that functional assays of immune system cells (such as quantification of phagocytosis) are an accessible and non-taxa-specific way to tease apart the effects of animals upregulating quantities of immune effectors (cells) and changes in the function of immune effectors (cellular performance) due to structural changes in cells such as those of membranes and enzymes. [ABSTRACT FROM AUTHOR]

Since the discovery of specific immune memory in invertebrates, researchers have investigated its immune response to diverse microbial and environmental stimuli. Nevertheless, the extent of the immune system’s interaction with metabolism, remains relatively enigmatic. In this mini review, we propose a comprehensive investigation into the intricate interplay between metabolism and specific immune memory. Our hypothesis is that cellular endocycles and epigenetic modifications play pivotal roles in shaping this relationship. Furthermore, we underscore the importance of the crosstalk between metabolism and specific immune memory for understanding the evolutionary costs. By evaluating these costs, we can gain deeper insights into the adaptive strategies employed by invertebrates in response to pathogenic challenges. Lastly, we outline future research directions aimed at unraveling the crosstalk between metabolism and specific immune memory. These avenues of inquiry promise to illuminate fundamental principles governing host-pathogen interactions and evolutionary trade-offs, thus advancing our understanding of invertebrate immunology.

Human activity changes multiple factors in the environment, which can have positive or negative synergistic effects on organisms. However, few studies have explored the causal effects of multiple anthropogenic factors, such as urbanization and invasive species, on animals and the mechanisms that mediate these interactions. This study examines the influence of urbanization on the detrimental effect of invasive avian vampire flies (Philornis downsi) on endemic Darwin's finches in the Galápagos Islands. We experimentally manipulated nest fly abundance in urban and non‐urban locations and then characterized nestling health, fledging success, diet, and gene expression patterns related to host defense. Fledging success of non‐parasitized nestlings from urban (79%) and non‐urban (75%) nests did not differ significantly. However, parasitized, non‐urban nestlings lost more blood, and fewer nestlings survived (8%) compared to urban nestlings (50%). Stable isotopic values (δ15N) from urban nestling feces were higher than those from non‐urban nestlings, suggesting that urban nestlings are consuming more protein. δ15N values correlated negatively with parasite abundance, which suggests that diet might influence host defenses (e.g., tolerance and resistance). Parasitized, urban nestlings differentially expressed genes within pathways associated with red blood cell production (tolerance) and pro‐inflammatory response (innate immunological resistance), compared to parasitized, non‐urban nestlings. In contrast, parasitized non‐urban nestlings differentially expressed genes within pathways associated with immunoglobulin production (adaptive immunological resistance). Our results suggest that urban nestlings are investing more in pro‐inflammatory responses to resist parasites but also recovering more blood cells to tolerate blood loss. Although non‐urban nestlings are mounting an adaptive immune response, it is likely a last effort by the immune system rather than an effective defense against avian vampire flies since few nestlings survived. [ABSTRACT FROM AUTHOR]

Comparative studies, especially of related species that span across ecoregions, have the potential to increase our understanding of different ecological or evolutionary pressures that may drive host–pathogen dynamics. We quantified differences in immune investment, via differential leukocyte counts and bacteria‐killing assays, across four closely related species of Gopherus tortoises, found across a gradient from the desert southwest to the subtropical southeast of the United States. We further quantified differences in a commensal nasal microbe (Pasteurella testudinis) and tested for associations among immune measures, P. testudinis, and previously quantified levels of the pathogen Mycoplasma agassizii and upper respiratory tract disease (URTD). We also evaluated the potential influence of environmental variables on immune investment, P. testudinis, and disease. We found that tortoise species in more arid environments had a reduced investment in inflammatory leukocytes, possibly as a strategy to reduce water loss, and invested more heavily in innate anti‐inflammatory leukocytes. Conversely, we found that species in moister, resource‐rich environments may face greater pathogen pressure, likely due to increased population densities and transmission rates among host tortoises. These tortoises had increased investment in inflammatory cells and appeared to reduce their nasal microbes (including P. testudinis) when they exhibited URTD. Thus, we quantified two negative correlational patterns: (1) between inflammatory responses and water conservation and (2) between resource quality and transmission rates. We hypothesize that these relationships across species may reflect variable development or evolution of innate immune functions. [ABSTRACT FROM AUTHOR]

Background: Living organisms face ubiquitous pathogenic threats and have consequently evolved immune systems to protect against potential invaders. However, many components of the immune system are physiologically costly to maintain and engage, often drawing resources away from other organismal processes such as growth and reproduction. Evidence from a diversity of systems has demonstrated that organisms use complex resource allocation mechanisms to manage competing needs and optimize fitness. However, understanding of resource allocation patterns is limited across taxa. Cnidarians, which include ecologically important organisms like hard corals, have been historically understudied in the context of resource allocations. Improving understanding of resource allocation-associated trade-offs in cnidarians is critical for understanding future ecological dynamics in the face of rapid environmental change. Methods: Here, we characterize trade-offs between constitutive immunity and reproduction in the facultatively symbiotic coral Astrangia poculata. Male colonies underwent ex situ spawning and sperm density was quantified. We then examined the effects of variable symbiont density and energetic budget on physiological traits, including immune activity and reproductive investment. Furthermore, we tested for potential trade-offs between immune activity and reproductive investment. Results: We found limited associations between energetic budget and immune metrics; melanin production was significantly positively associated with carbohydrate concentration. However, we failed to document any associations between immunity and reproductive output which would be indicative of trade-offs, possibly due to experimental limitations. Our results provide a preliminary framework for future studies investigating immune trade-offs in cnidarians. [ABSTRACT FROM AUTHOR]

Background: Pathogens face strong selection from host immune responses, yet many host populations support pervasive pathogen populations. We investigated this puzzle in a model system of Bartonella and rodents from Israel's northwestern Negev Desert. We chose to study this system because, in this region, 75–100% of rodents are infected with Bartonella at any given time, despite an efficient immunological response. In this region, Bartonella species circulate in three rodent species, and we tested the hypothesis that at least one of these hosts exhibits a waning immune response to Bartonella, which allows reinfections. Methods: We inoculated captive animals of all three rodent species with the same Bartonella strain, and we quantified the bacterial dynamics and Bartonella-specific immunoglobulin G antibody kinetics over a period of 139 days after the primary inoculation, and then for 60 days following reinoculation with the same strain. Results: Contrary to our hypothesis, we found a strong, long-lasting immunoglobulin G antibody response, with protective immunological memory in all three rodent species. That response prevented reinfection upon exposure of the rodents to the same Bartonella strain. Conclusions: This study constitutes an initial step toward understanding how the interplay between traits of Bartonella and their hosts influences the epidemiological dynamics of these pathogens in nature. [ABSTRACT FROM AUTHOR]

How do large and small reptiles defend against infections, given the consequences of body mass for physiology and disease transmission? Functionally equivalent mammalian and avian granulocytes increased disproportionately with body mass (i.e., scaled hypermetrically), such that large organisms had higher concentrations than expected by a prediction of proportional protection across sizes. However, as these scaling relationships were derived from endothermic animals, they do not necessarily inform the scaling of leukocyte concentration for ectothermic reptiles that have a different physiology and evolutionary history. Here, we asked whether and how lymphocyte and heterophil concentrations relate to body mass among more than 120 reptile species. We compared these relationships to those found in birds and mammals and to existing scaling frameworks (i.e., protecton, complexity, rate of metabolism, or safety factor hypotheses). Both lymphocyte and heterophil concentrations scaled almost isometrically among reptiles. In contrast, functionally equivalent granulocytes scaled hypermetrically and lymphocytes scaled isometrically in birds and mammals. Life history traits were also poor predictors of variation in reptilian heterophil and lymphocyte concentrations. Our results provide insight into differences in immune protection in birds and mammals relative to that in reptiles through a comparative lens. The shape of scaling relationships differs, which should be considered when modeling disease dynamics among these groups. [ABSTRACT FROM AUTHOR]

The field of ecological immunology, or ecoimmunology, has provided valuable insights on the immune responses of diverse host organisms threatened by infectious diseases in many different environments. One infectious disease that has been particularly notable for its impacts on host populations is amphibian chytridiomycosis, which has been linked with amphibian declines around the world. Amphibian immune responses to the pathogen that causes chytridiomycosis (Batrachochytriym dendrobatidis) are not well understood but thought to involve innate immune factors, including the complement system. In this study, we tested the ability of complement proteins to inhibit B. dendrobatidis in in vitro challenge assays. We found that complement proteins from amphibian plasma that were not heat inactivated reduced the viability and growth of B. dendrobatidis. The inhibitory efficacy was similar to effects on Pseudomonas fluorescens, a bacterium that is known to be inhibited by complement protein activation. These findings suggest inhibition of B. dendrobatidis that is consistent with the involvement of the complement system. In addition, we provide methods for standardizing pathogen killing assays, and set a foundation for further investigations on the amphibian complement system and other immune responses to amphibian chytridiomycosis.

Abstract Background Pathogens face strong selection from host immune responses, yet many host populations support pervasive pathogen populations. We investigated this puzzle in a model system of Bartonella and rodents from Israel’s northwestern Negev Desert. We chose to study this system because, in this region, 75–100% of rodents are infected with Bartonella at any given time, despite an efficient immunological response. In this region, Bartonella species circulate in three rodent species, and we tested the hypothesis that at least one of these hosts exhibits a waning immune response to Bartonella, which allows reinfections. Methods We inoculated captive animals of all three rodent species with the same Bartonella strain, and we quantified the bacterial dynamics and Bartonella-specific immunoglobulin G antibody kinetics over a period of 139 days after the primary inoculation, and then for 60 days following reinoculation with the same strain. Results Contrary to our hypothesis, we found a strong, long-lasting immunoglobulin G antibody response, with protective immunological memory in all three rodent species. That response prevented reinfection upon exposure of the rodents to the same Bartonella strain. Conclusions This study constitutes an initial step toward understanding how the interplay between traits of Bartonella and their hosts influences the epidemiological dynamics of these pathogens in nature. Graphical Abstract

Background Living organisms face ubiquitous pathogenic threats and have consequently evolved immune systems to protect against potential invaders. However, many components of the immune system are physiologically costly to maintain and engage, often drawing resources away from other organismal processes such as growth and reproduction. Evidence from a diversity of systems has demonstrated that organisms use complex resource allocation mechanisms to manage competing needs and optimize fitness. However, understanding of resource allocation patterns is limited across taxa. Cnidarians, which include ecologically important organisms like hard corals, have been historically understudied in the context of resource allocations. Improving understanding of resource allocation-associated trade-offs in cnidarians is critical for understanding future ecological dynamics in the face of rapid environmental change. Methods Here, we characterize trade-offs between constitutive immunity and reproduction in the facultatively symbiotic coral Astrangia poculata. Male colonies underwent ex situ spawning and sperm density was quantified. We then examined the effects of variable symbiont density and energetic budget on physiological traits, including immune activity and reproductive investment. Furthermore, we tested for potential trade-offs between immune activity and reproductive investment. Results We found limited associations between energetic budget and immune metrics; melanin production was significantly positively associated with carbohydrate concentration. However, we failed to document any associations between immunity and reproductive output which would be indicative of trade-offs, possibly due to experimental limitations. Our results provide a preliminary framework for future studies investigating immune trade-offs in cnidarians.

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]

This short review focuses on current experimental designs to quantify immune acclimation in animals. Especially in the face of rapidly changing thermal regimes, thermal acclimation of immune function has the potential to impact host–pathogen relationships and the fitness of hosts. While much of the field of ecoimmunology has focused on vertebrates and insects, broad interest in how animals can acclimate to temperatures spans taxa. The literature shows a recent increase in thermal acclimation studies in the past six years. I categorized studies as focusing on (1) natural thermal variation in the environment (e.g., seasonal), (2) in vivo manipulation of animals in captive conditions, and (3) in vitro assays using biological samples taken from wild or captive animals. I detail the strengths and weaknesses of these approaches, with an emphasis on mechanisms of acclimation at different levels of organization (organismal and cellular). These two mechanisms are not mutually exclusive, and a greater combination of the three techniques listed above will increase our knowledge of the diversity of mechanisms used by animals to acclimate to changing thermal regimes. Finally, I suggest that functional assays of immune system cells (such as quantification of phagocytosis) are an accessible and non-taxa-specific way to tease apart the effects of animals upregulating quantities of immune effectors (cells) and changes in the function of immune effectors (cellular performance) due to structural changes in cells such as those of membranes and enzymes.

The immune equilibrium model suggests that exposure to microbes during early life primes immune responses for pathogen exposure later in life. While recent studies using a range of gnotobiotic (germ-free) model organisms offer support for this theory, we currently lack a tractable model system for investigating the influence of the microbiome on immune system development. Here, we used an amphibian species (Xenopus laevis) to investigate the importance of the microbiome in larval development and susceptibility to infectious disease later in life. We found that experimental reductions of the microbiome during embryonic and larval stages effectively reduced microbial richness, diversity and altered community composition in tadpoles prior to metamorphosis. In addition, our antimicrobial treatments resulted in few negative effects on larval development, body condition, or survival to metamorphosis. However, contrary to our predictions, our antimicrobial treatments did not alter susceptibility to the lethal fungal pathogen Batrachochytrium dendrobatidis (Bd) in the adult life stage. While our treatments to reduce the microbiome during early development did not play a critical role in determining susceptibility to disease caused by Bd in X. laevis, they nevertheless indicate that developing a gnotobiotic amphibian model system may be highly useful for future immunological investigations. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'. [ABSTRACT FROM AUTHOR]

Variation in food resources can result in dramatic fluctuations in the body condition of animals dependent on those resources. Decreases in body mass can disrupt patterns of energy allocation and impose stress, thereby altering immune function. In this study, we investigated links between changes in body mass of captive cane toads (Rhinella marina), their circulating white blood cell populations, and their performance in immune assays. Captive toads that lost weight over a three-month period had increased levels of monocytes and heterophils and reduced levels of eosinophils. Basophil and lymphocyte levels were unrelated to changes in mass. Because individuals that lost mass had higher heterophil levels but stable lymphocyte levels, the ratio of these cell types was also higher, partially consistent with a stress response. Phagocytic ability of whole blood was higher in toads that lost mass, owing to increased circulating levels of phagocytic cells. Other measures of immune performance were unrelated to mass change. These results highlight the challenges faced by invasive species as they expand their range into novel environments which may impose substantial seasonal changes in food availability that were not present in the native range. Individuals facing energy restrictions may shift their immune function towards more economical and general avenues of combating pathogens. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'. [ABSTRACT FROM AUTHOR]

Greater knowledge of how host–microbiome interactions vary with anthropogenic environmental change and influence pathogenic infections is needed to better understand stress-mediated disease outcomes. We investigated how increasing salinization in freshwaters (e.g. due to road de-icing salt runoff) and associated increases in growth of nutritional algae influenced gut bacterial assembly, host physiology and responses to ranavirus exposure in larval wood frogs (Rana sylvatica). Elevating salinity and supplementing a basic larval diet with algae increased larval growth and also increased ranavirus loads. However, larvae given algae did not exhibit elevated kidney corticosterone levels, accelerated development or weight loss post-infection, whereas larvae fed a basic diet did. Thus, algal supplementation reversed a potentially maladaptive stress response to infection observed in prior studies in this system. Algae supplementation also reduced gut bacterial diversity. Notably, we observed higher relative abundances of Firmicutes in treatments with algae—a pattern consistent with increased growth and fat deposition in mammals—that may contribute to the diminished stress responses to infection via regulation of host metabolism and endocrine function. Our study informs mechanistic hypotheses about the role of microbiome mediation of host responses to infection that can be tested in future experiments in this host–pathogen system. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'. [ABSTRACT FROM AUTHOR]

Glucocorticoid (GC) release is triggered by adverse stimuli that activate the hypothalamus-pituitary-adrenal/interrenal axis. Glucocorticoids may enhance or suppress immune functions depending on the level of elevation. In this study, we investigated the effects of transient and chronic increase of corticosterone (CORT) on the wound healing of the American bullfrog. Frogs were submitted to a daily transdermal hormonal application that acutely elevated CORT plasma levels, or vehicle as a control. Other frogs were surgically implanted with a silastic tube filled with CORT that resulted in chronic elevation of CORT plasma levels or received empty implants as a control. A dermal biopsy was performed to create a wound and was photographed every 3 days. Individuals treated with transdermal CORT started healing faster than their control 32 days after the biopsy. Frogs that received CORT implants tended to heal slower than control subjects. Plasma bacterial killing ability was not affected by treatment, which reinforces the constitutive nature of this innate immune trait. By the end of the experiment, frogs from the acute CORT treatment had smaller wounds compared with those receiving the CORT-filled implants, highlighting the differential effects of acute (immunoenhancing) and chronic (immunosuppressive) elevation of CORT plasma levels. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'. [ABSTRACT FROM AUTHOR]

Testosterone (T) regulates immune function, with both immunostimulatory and immunosuppressive effects on several vertebrates. We investigated the covariation between plasma T and corticosterone (CORT) levels and immunity (plasma bacterial killing ability (BKA), and neutrophil to lymphocyte ratio (NLR)) in free-living Rhinella icterica male toads inside and outside the reproductive season. We found an overall positive correlation between steroids and immune traits, with toads during the reproductive season displaying increased T, CORT and BKA. We also investigated the T transdermal application effects on T, CORT, phagocytosis of blood cells, BKA and NLR in captive toads. Toads were treated with T (1, 10 or 100 µg) or vehicle (sesame oil) for eight consecutive days. Animals were bled on the first and eighth days of treatment. Increased plasma T was observed on the first and last day of T-treatment, while increased BKA was observed following all T doses on the last day, with a positive correlation between T and BKA. Plasma CORT, NLR and phagocytosis increased on the last day for all T-treated and vehicle groups. Overall, we demonstrated a positive covariation between T and immune traits in the field and T-induced augmented BKA in captive toads, indicating a T immunoenhancing effect in R. icterica males. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'. [ABSTRACT FROM AUTHOR]

Wild animals are under constant threat from a wide range of micro‐ and macroparasites in their environment. Animals make immune responses against parasites, and these are important in affecting the dynamics of parasite populations. Individual animals vary in their anti‐parasite immune responses. Genetic polymorphism of immune‐related loci contributes to inter‐individual differences in immune responses, but most of what we know in this regard comes from studies of humans or laboratory animals; there are very few such studies of wild animals naturally infected with parasites. Here we have investigated the effect of single nucleotide polymorphisms (SNPs) in immune‐related loci (the major histocompatibility complex [MHC], and loci coding for cytokines and Toll‐like receptors) on a wide range of immune and infection phenotypes in UK wild house mice, Mus musculus domesticus. We found strong associations between SNPs in various MHC and cytokine‐coding loci on both immune measures (antibody concentration and cytokine production) and on infection phenotypes (infection with mites, worms and viruses). Our study provides a comprehensive view of how polymorphism of immune‐related loci affects immune and infection phenotypes in naturally infected wild rodent populations. [ABSTRACT FROM AUTHOR]

Individuals differ in the nature of the immune responses they produce, affecting disease susceptibility and ultimately health and fitness. These differences have been hypothesized to have an origin in events experienced early in life that then affect trajectories of immune development and responsiveness. Here, we investigate how early‐life immune expression profiles influence life history outcomes in a natural population of field voles, Microtus agrestis, in which we are able to monitor variation between and within individuals through time by repeat sampling of individually marked animals. We analysed the co‐expression of 20 immune genes in early life to create a correlation network consisting of three main clusters, one of which (containing Gata3, Il10 and Il17) was associated with later‐life reproductive success and susceptibility to chronic bacterial (Bartonella) infection. More detailed analyses supported associations between early‐life expression of Il17 and reproductive success later in life, and of Il10 expression early in life and later infection with Bartonella. We also found significant association between an Il17 genotype and the early‐life expression of Il10. Our results demonstrate that immune expression profiles can be manifested during early life with effects that persist through adulthood and that shape the variability among individuals in susceptibility to infection and fitness widely seen in natural populations. [ABSTRACT FROM AUTHOR]

Habitat fragmentation is an important driver of biodiversity loss and can be remediated through management actions aimed at maintenance of natural connectivity in metapopulations. Connectivity may protect populations from infectious diseases by preserving immunogenetic diversity and disease resistance. However, connectivity could exacerbate the risk of infectious disease spread across vulnerable populations.We tracked the spread of a novel strain of Mycoplasma ovipneumoniae in a metapopulation of desert bighorn sheep Ovis canadensis nelsoni in the Mojave Desert to investigate how variation in connectivity among populations influenced disease outcomes.M. ovipneumoniae was detected throughout the metapopulation, indicating that the relative isolation of many of these populations did not protect them from pathogen invasion. However, we show that connectivity among bighorn sheep populations was correlated with higher immunogenetic diversity, a protective immune response and lower disease prevalence. Variation in protective immunity predicted infection risk in individual bighorn sheep and was associated with heterozygosity at genetic loci linked to adaptive and innate immune signalling.Together, these findings may indicate that population connectivity maintains immunogenetic diversity in bighorn sheep populations in this system and has direct effects on immune responses in individual bighorn sheep and their susceptibility to infection by a deadly pathogen.Our study suggests that the genetic benefits of population connectivity could outweigh the risk of infectious disease spread and supports conservation management that maintains natural connectivity in metapopulations. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are volatile and short-lived molecules playing important roles in several physiological functions, including immunity and physiological adaptation to unsuitable environmental conditions. In an eco-immunological view, the energetic costs associated with an advantageous metabolic apparatus able to cope with wide changes in environmental parameters, e.g., temperature range, water salinity or drought, could be further balanced by the advantages that this apparatus may also represent in other situations, e.g., during the immune response. This review provides an overview of molluscs included in the IUCN list of the worst invasive species, highlighting how their relevant capacity to manage ROS production during physiologically challenging situations can also be advantageously employed during the immune response. Current evidence suggests that a relevant capacity to buffer ROS action and their damaging consequences is advantageous in the face of both environmental and immunological challenges, and this may represent a trait for potential invasiveness. This should be considered in order to obtain or update information when investigating the potential of the invasiveness of emerging alien species, and also in view of ongoing climate changes. [ABSTRACT FROM AUTHOR]

Historically, investigations of how organismal investments in immunity fluctuate in response to environmental and physiological changes have focused on seasonally breeding organisms that confine reproduction to seasons with relatively unchallenging environmental conditions and abundant resources. The red crossbill, Loxia curvirostra, is a songbird that can breed opportunistically if conifer seeds are abundant, on both short, cold, and long, warm days, providing an ideal system to investigate environmental and reproductive effects on immunity. In this study, we measured inter- and intra-annual variation in complement, natural antibodies, PIT54 and leucocytes in crossbills across four summers (2010-2013) and multiple seasons within 1 year (summer 2011-spring 2012). Overall, we observed substantial changes in crossbill immune investment among summers, with interannual variation driven largely by food resources, while variation across multiple seasons within a single cone year was less pronounced and lacked a dominant predictor of immune investment. However, we found weak evidence that physiological processes (e.g. reproductive condition, moult) or abiotic factors (e.g. temperature, precipitation) affect immune investment. Collectively, this study suggests that a reproductively flexible organism may be able to invest in both reproduction and survival-related processes, potentially by exploiting rich patches with abundant resources. More broadly, these results emphasize the need for more longitudinal studies of trade-offs associated with immune investment.

Ecoimmunology affords us the ability to better understand immunological processes through consideration of external factors, such as the thermal microenvironment. This consideration is imperative when examining the immunological processes of ectothermic organisms like reptiles. Reptiles uniquely rely heavily on their innate immune function but remain poorly understood in immunological studies. In this study, we examined innate immunity in two zoo‐housed tortoise species, the Indian star tortoise (Geochelone elegans, Schoepff, 1795) and northern spider tortoise (Pyxis arachnoides brygooi, Vuillemin & Domergue, 1972). Bacterial killing assays (BKAs) were optimized and used to assess the monthly immunocompetence of these tortoises to three different bacteria: Escherichia coli, Salmonella enterica, and Staphylococcus aureus. We evaluated differences in blood biochemistry values (lactate and glucose) among months and species as well as fecal corticosterone (CORT) between species. Lastly, we examined the potential influences of individual thermal microenvironments on bactericidal ability. Both G. elegans and P. a. brygooi demonstrated immunocompetence against all bacterial challenges, but only bactericidal ability against E. coli varied over months. Optimal BKA serum dilutions, blood glucose levels, and fecal CORT concentrations differed between the two species. Finally, there was evidence that the thermal microenvironment influenced the tortoises' bactericidal ability against E. coli. Through use of nonmodel organisms, such as tortoises, we are given insight into the inner workings of innate immunity and a better understanding of the complexities of the vertebrate immune system. Research Highlights: •Innate immune ability and fecal corticosterone concentrations were species‐specific. •Bactericidal ability against Escherichia coli had a relationship with the thermal microenvironment. [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]

IntroductionInteractions between the gut microbiome (GM) and the immune system influence host health and fitness. However, few studies have investigated this link and GM dynamics during disease in wild species. Bats (Mammalia: Chiroptera) have an exceptional ability to cope with intracellular pathogens and a unique GM adapted to powered flight. Yet, the contribution of the GM to bat health, especially immunity, or how it is affected by disease, remains unknown.MethodsHere, we examined the dynamics of the Egyptian fruit bats’ (Rousettus aegyptiacus) GM during health and disease. We provoked an inflammatory response in bats using lipopolysaccharides (LPS), an endotoxin of Gram-negative bacteria. We then measured the inflammatory marker haptoglobin, a major acute phase protein in bats, and analyzed the GM (anal swabs) of control and challenged bats using high-throughput 16S rRNA sequencing, before the challenge, 24h and 48h post challenge.ResultsWe revealed that the antigen challenge causes a shift in the composition of the bat GM (e.g., Weissella, Escherichia, Streptococcus). This shift was significantly correlated with haptoglobin concentration, but more strongly with sampling time. Eleven bacterial sequences were correlated with haptoglobin concentration and nine were found to be potential predictors of the strength of the immune response, and implicit of infection severity, notably Weissella and Escherichia. The bat GM showed high resilience, regaining the colony’s group GM composition rapidly, as bats resumed foraging and social activities.ConclusionOur results demonstrate a tight link between bat immune response and changes in their GM, and emphasize the importance of integrating microbial ecology in ecoimmunological studies of wild species. The resilience of the GM may provide this species with an adaptive advantage to cope with infections and maintain colony health.

[Display omitted] • CORT and T are higher during reproductive season, especially in calling males toads. • Higher BKA during reproduction suggests immune-enhancing effect of steroids. • BKA and NLR are positively correlated with CORT and T. • Stress response is yearly constant, decreasing BKA only after reproductive season. Theoretical models predict that elevated androgen and glucocorticoid levels in males during the reproductive season promote immunosuppression. However, some studies report decreased stress response during this season. This study investigated annual variation in plasma corticosterone and testosterone levels, plasma bacterial killing ability (BKA), and neutrophil to lymphocyte ratio (NLR) in free-living male toads (Rhinella icterica). Toads were sampled in the field (baseline) and 1 h-post restraint over five months, and we considered the occurrence of vocal activity. Baseline corticosterone, testosterone, and BKA showed higher values during the reproductive period, specifically in calling male toads. The NLR was similar throughout the year, but higher values were observed in calling toads. Moreover, baseline NLR and BKA were positively correlated with both testosterone and corticosterone, suggesting higher steroid levels during reproduction are associated with enhanced cellular and humoral immunity. Despite fluctuation of baseline values, post-restraint corticosterone levels remained uniform over the year, indicating that toads reached similar maximum values throughout the year. Testosterone levels decreased following restraint before one specific reproductive period but increased in response to restraint during and after this period. Meanwhile, BKA decreased due to restraint only after the reproductive period, indicating immune protection and resilience to immunosuppression by stressors associated with steroid hormones during reproduction. Our results show that baseline and stress-induced hormonal and immune regulation varies throughout the year and are associated with vocal activity in R. icterica males, indicating a possible compromise between steroids and immune function in anuran males. [ABSTRACT FROM AUTHOR]

Many studies have used the avian hemosporidians (Leucocytozoon, Plasmodium, and Hemoproteus) to test hypotheses of host-parasite co-evolution, yet documented health and survival consequences of these blood parasites vary among studies and generalizations about their pathogenicity are debatable. In general, the negative effects of the hemosporidians are likely to be greatest during acute infections of young birds, yet most previous studies in wild passerines have examined chronic effects in adults. Here, we evaluated responses of nestling American crows (Corvus brachyrhynchos) to acute infection (prevalence and burden), as well as its short- and long-term survival consequences. We used panel of nine hematological and biochemical parameters that are regularly used to evaluate the health of domestic animals, including leukocyte profiles, hematocrit, and plasma proteins. We assessed the effects of infection on survival in a mark-recapture framework. Overall, 56% of crows (n = 321 samples) were infected by at least one of the three genera. Infections by all genera were associated with elevated plasma proteins and globulins, which could indicate an adaptive immune response. However, only Plasmodium infections were associated with low hematocrit (anemia) and lower fledging success, possibly mediated by the negative effect of low hematocrit values on body condition. Moreover, early Plasmodium infection (

This article discusses mythical and real dangerous of ecology and health. In response to it, they produce mycotoxins, this is their way of protection, like snakes. The production of mycotoxins especially increases when soils are contaminated with pesticides, as well as in dry years. In these cases, even edible mushrooms become poisonous. Therefore, in conditions of unfavorable ecology, mushrooms must be collected very carefully. [ABSTRACT FROM AUTHOR]

The original hygiene hypothesis proposed that certain diseases derive from low levels of early-life microbial exposure. Since then, the hypothesis has been applied to numerous inflammatory, autoimmune, and allergic conditions. The changes in hygiene linked to these diseases include numerous changes in biotic exposure and lifestyle. To this end, some scholars have called for abandonment of the term or have suggested alternate labels, e.g., the old friends hypothesis. However, neither of these terms encompasses the complexity of plasticity in immune response and host–parasite/commensal interactions that influence these conditions. Here, I review this complexity, with particular regard to the factors affecting immunological strategies, the development of tolerance, immune dysfunction, and ecological interactions among organisms. I discuss the biotic factors that affect immune plasticity and how these interact with abiotic factors such as nutrition, as well as how transgenerational exposures may affect immune plasticity. Finally, I review the general features of diseases linked to biotic exposures. [ABSTRACT FROM AUTHOR]

While most research on sexual signals as indicators of health status and infection has been focused on communication by visual (color), airborne acoustic (song structure, amplitude, frequency, and pattern), or chemical means, new evidence suggests that substrate‐borne vibratory signals can also be a reliable indicator of male quality and possibly infection history. In this study, we investigated the ability of the vibratory cues in multimodal sexual signals of Schizocosa ocreata wolf spiders to convey male health information to a female, and whether females adjust their mate choice decisions based on these cues. Individual components of the complete vibratory signal, including stridulatory pulse rate, mean amplitude, and peak amplitude, were all significant predictors of mating success in live trials. Males infected as a juvenile (during the penultimate molt) had significantly lower stridulatory rate and peak amplitude than control males. There were no significant differences in any of the vibratory signal components between control males and males infected as adults (1 h prior to mating trials). This suggests that the vibratory cues in this species may be altered when infection occurs during development, allowing females to avoid males that have been immunocompromised in the past. However, these cues are not reliable indicators of whether a male is actively infected, which means that the evaluation of these cues will not help a female avoid contact with infected individuals. Taken together, these results suggest that vibratory signals may convey honest information about male quality and past health, allowing females to choose mates that have not been compromised during development. [ABSTRACT FROM AUTHOR]

Bottom‐up (plant) and top‐down (natural enemy) trophic factors can interact to have significant influence on the diet breadth of herbivores. For herbivorous insects that are victim to parasitoid attacks, diet composition can modulate insect immune responses against the parasitoid. However, immune responses are costly and insect herbivores experience a trade‐off between investment in immune defences and other physiological processes.We used a split‐brood laboratory experiment to explore how the diet of the fall webworm (Hyphantria cunea), a species that eats over 400 plant species, affects larval growth and fitness and cellular immune response to attacks from a parasitic wasp. We reared larvae on four different plant diets (apple, alder, chokecherry, cottonwood) and then exposed them to an immune challenge from a parasitoid attack.We found that diet influenced larval development as well as parameters indicative of immune response. Larvae reared on the plant that led to the poorest development also had the fewest granulocytes and the highest odds of containing a parasitoid larva. However, larval growth was not a predictor of immune response.Overall, we show that the bottom‐up effect of diet variability has significant impacts on insect immune response such that larval fitness varies considerably when fed different dietary plant species. Broad diet ranges may offer herbivorous insects the opportunity to exploit a different set of resources depending on the severity of top‐down pressures. Here, we show that this variability in plant quality also has significant impacts on larval immune response. [ABSTRACT FROM AUTHOR]

Living organisms are vulnerable to thermal stress, which causes a diversity of physiological outcomes. Previous work has shown that the snail vectors (Biomphalaria glabrata) of an important human pathogen, Schistosoma mansoni, revert from resistant to susceptible after short exposure to a heat stress as low as 31°C; however, due to lack of replicability among labs and genetic lines of snails, it has been hypothesized that this effect is genotype dependent. We examined the effects of heat shock on the resistance of two species of snail vectors including B. glabrata and Biomphalaria sudanica. We used three different inbred laboratory snail lines in addition to the F1 generation of field‐collected snails from Lake Victoria, Kenya, an area with high levels of schistosomiasis transmission. Our results showed marginal effects of heat shock on prevalence of infection in B. glabrata, and that this response was genotype specific. We found no evidence of a heat shock effect on prevalence of infection in B. sudanica or on intensity of infection (number of infectious stages shed) in either snail species. Such environmentally influenced defense responses stress the importance of considering this unique interaction between snail and parasite genotypes in determining infection dynamics under climate changes. [ABSTRACT FROM AUTHOR]

Abstract Living organisms are vulnerable to thermal stress, which causes a diversity of physiological outcomes. Previous work has shown that the snail vectors (Biomphalaria glabrata) of an important human pathogen, Schistosoma mansoni, revert from resistant to susceptible after short exposure to a heat stress as low as 31°C; however, due to lack of replicability among labs and genetic lines of snails, it has been hypothesized that this effect is genotype dependent. We examined the effects of heat shock on the resistance of two species of snail vectors including B. glabrata and Biomphalaria sudanica. We used three different inbred laboratory snail lines in addition to the F1 generation of field‐collected snails from Lake Victoria, Kenya, an area with high levels of schistosomiasis transmission. Our results showed marginal effects of heat shock on prevalence of infection in B. glabrata, and that this response was genotype specific. We found no evidence of a heat shock effect on prevalence of infection in B. sudanica or on intensity of infection (number of infectious stages shed) in either snail species. Such environmentally influenced defense responses stress the importance of considering this unique interaction between snail and parasite genotypes in determining infection dynamics under climate changes.

Reactive oxygen species (ROS) are volatile and short-lived molecules playing important roles in several physiological functions, including immunity and physiological adaptation to unsuitable environmental conditions. In an eco-immunological view, the energetic costs associated with an advantageous metabolic apparatus able to cope with wide changes in environmental parameters, e.g., temperature range, water salinity or drought, could be further balanced by the advantages that this apparatus may also represent in other situations, e.g., during the immune response. This review provides an overview of molluscs included in the IUCN list of the worst invasive species, highlighting how their relevant capacity to manage ROS production during physiologically challenging situations can also be advantageously employed during the immune response. Current evidence suggests that a relevant capacity to buffer ROS action and their damaging consequences is advantageous in the face of both environmental and immunological challenges, and this may represent a trait for potential invasiveness. This should be considered in order to obtain or update information when investigating the potential of the invasiveness of emerging alien species, and also in view of ongoing climate changes.

Ecological context—the biotic and abiotic environment, along with its influence on population mixing dynamics and individual susceptibility—is thought to have major bearing on epidemic outcomes. However, direct comparisons of wildlife disease events in contrasting ecological contexts are often confounded by concurrent differences in host genetics, exposure histories, or pathogen strains. Here, we compare disease dynamics of a Mycoplasma ovipneumoniae spillover event that affected bighorn sheep populations in two contrasting ecological contexts. One event occurred on the herd's home range near the Rio Grande Gorge in New Mexico, while the other occurred in a captive facility at Hardware Ranch in Utah. While data collection regimens varied, general patterns of antibody signal strength and symptom emergence were conserved between the two sites. Symptoms appeared in the captive setting an average of 12.9 days postexposure, average time to seroconversion was 24.9 days, and clinical signs peaked at approximately 36 days postinfection. These patterns were consistent with serological testing and subsequent declines in symptom intensity in the free‐ranging herd. At the captive site, older animals exhibited more severe declines in body condition and loin thickness, higher symptom burdens, and slower antibody response to the pathogen than younger animals. Younger animals were more likely than older animals to clear infection by the time of sampling at both sites. The patterns presented here suggest that environment may not be a major determinant of epidemiological outcomes in the bighorn sheep—M. ovipneumoniae system, elevating the possibility that host‐ or pathogen‐factors may be responsible for observed variation. [ABSTRACT FROM AUTHOR]

The widely-distributed North American species Peromyscus leucopus and P. maniculatus of cricetine rodents are, between them, important natural reservoirs for several zoonotic diseases of humans: Lyme disease, human granulocytic anaplasmosis, babesiosis, erhlichiosis, hard tickborne relapsing fever, Powassan virus encephalitis, hantavirus pulmonary syndrome, and plague. While these infections are frequently disabling and sometimes fatal for humans, the peromyscines display little pathology and apparently suffer few consequences, even when prevalence of persistent infection in a population is high. While these Peromyscus spp. are unable to clear some of the infections, they appear to have partial resistance, which limits the burden of the pathogen. In addition, they display traits of infection tolerance, which reduces the damage of the infection. Research on these complementary resistance and tolerance phenomena in Peromyscus has relevance both for disease control measures targeting natural reservoirs and for understanding the mechanisms of the comparatively greater sickness of many humans with these and other infections.

Abstract Ecological context—the biotic and abiotic environment, along with its influence on population mixing dynamics and individual susceptibility—is thought to have major bearing on epidemic outcomes. However, direct comparisons of wildlife disease events in contrasting ecological contexts are often confounded by concurrent differences in host genetics, exposure histories, or pathogen strains. Here, we compare disease dynamics of a Mycoplasma ovipneumoniae spillover event that affected bighorn sheep populations in two contrasting ecological contexts. One event occurred on the herd's home range near the Rio Grande Gorge in New Mexico, while the other occurred in a captive facility at Hardware Ranch in Utah. While data collection regimens varied, general patterns of antibody signal strength and symptom emergence were conserved between the two sites. Symptoms appeared in the captive setting an average of 12.9 days postexposure, average time to seroconversion was 24.9 days, and clinical signs peaked at approximately 36 days postinfection. These patterns were consistent with serological testing and subsequent declines in symptom intensity in the free‐ranging herd. At the captive site, older animals exhibited more severe declines in body condition and loin thickness, higher symptom burdens, and slower antibody response to the pathogen than younger animals. Younger animals were more likely than older animals to clear infection by the time of sampling at both sites. The patterns presented here suggest that environment may not be a major determinant of epidemiological outcomes in the bighorn sheep—M. ovipneumoniae system, elevating the possibility that host‐ or pathogen‐factors may be responsible for observed variation.

The red-leg syndrome in amphibians is a condition commonly associated with the bacteria Aeromonas hydrophila and has led to population declines. However, there is little information concerning the inflammatory assemblage in infected anurans. We evaluated immune and endocrine alterations induced by stimulation with heat-killed A. hydrophila injected in Rhinella diptycha toads. Control animals were not manipulated, while the others were separated into groups that received intraperitoneal injection of 300 μl of saline or heat-killed bacteria: groups A1 (3 × 107 cells), A2 (3 × 108 cells), and A3 (3 × 109 cells). Animals were bled and euthanized six hours post-injection. We evaluated neutrophil: lymphocyte ratio (NLR), plasma bacterial killing ability (BKA), testosterone (T), melatonin (MEL), and corticosterone (CORT) plasma levels. Heat-killed A. hydrophila increased CORT and NLR, and decreased MEL, especially at higher concentrations. There was no effect of treatment on T and BKA. We then selected the saline and A3 groups to conduct mRNA expression of several genes including glucocorticoid receptor (GR), toll-like receptor-4 (TLR-4), interferon-γ (IFN-γ), interleukin (IL)-1β, IL-6, and IL-10. We found higher expression of IL-6, IL-1β, IL-10, and IFN-γ in group A3 compared to the saline group. These results indicate the beginning of an inflammatory assemblage, notably at the two highest concentrations of bacteria, and give a better understanding of how anurans respond to an infection within an integrated perspective, evaluating different physiological aspects. Future studies should investigate later phases of the immune response to elucidate more about the inflammation in amphibians challenged with A. hydrophila. [Display omitted] • Heat-killed Aeromonas hydrophila induces higher NLR and plasma CORT levels in toads • Circulating MEL levels decrease in toads after bacterial stimulation • IL-1β, IL-6, IFN-ℽ, IL-10 had higher mRNA levels in bacterial stimulated toads • Bacterial stimulation induced similar changes to LPS treatment in toads • The inflammatory assemblage is in the acute phase six hours after immune challenge [ABSTRACT FROM AUTHOR]

Migration is energetically expensive and is predicted to drive similar morphological adaptations and physiological trade‐offs in migratory bats and birds. Previous studies suggest that fixed traits like wing morphology vary among species and individuals according to selective pressures on flight, while immune defences can vary flexibly within individuals as energy is variably reallocated throughout the year.We assessed intraspecific variation in wing morphology and immune function in silver‐haired bats Lasionycteris noctivagans, a species that follows both partial and differential migration patterns. We hypothesized that if bats experience energy constraints associated with migration, then wing morphology and immune function should vary based on migratory tendency (sedentary or migratory) and migration distance. We predicted that long‐distance migrants would have reduced immune function and more migration‐adapted wing shapes compared to resident or short‐distance migrating bats.We estimated breeding latitude of spring migrants using stable hydrogen isotope techniques. Our sample consisted primarily of male bats, which we categorized as residents, long‐distance northern migrants, short‐distance northern migrants and southern migrants (apparent breeding location south of capture site). Controlling for individual condition and capture date, we related wing characteristics and immune indices among groups.Some, but not all, aspects of wing form and immune function varied between migrants and residents. Long‐distance northern migrants had larger wings than short‐distance northern migrants and lower wing loading than southern migrants. Compared with resident bats, short‐distance northern migrants had reduced IgG while southern migrants had heightened neutrophils and neutrophil‐to‐lymphocyte ratios. Body fat, aspect ratio, wing tip shape and bacteria killing ability did not vary with migration status or distance.In general, male silver‐haired bats do not appear to mediate migration costs by substantially downregulating immune defences or to be under stronger selection for wing forms adapted for fast, energy‐efficient flight. Such phenotypic changes may be more adaptive for female silver‐haired bats, which migrate farther and are more constrained by time in spring than males. Adaptations for aerial hawking and the use of heterothermy by migrating bats may also reduce the energetic cost of migration and the need for more substantial morphological and physiological trade‐offs. [ABSTRACT FROM AUTHOR]

The apparent ability of bats to harbor many virulent viruses without showing disease is likely driven by distinct immune responses that coevolved with mammalian flight and the exceptional longevity of this order. Yet our understanding of the immune mechanisms of viral tolerance is restricted to a small number of bat-virus relationships and remains poor for coronaviruses (CoVs), despite their relevance to human health. Proteomics holds particular promise for illuminating the immune factors involved in bat responses to infection, because it can accommodate especially low sample volumes (e.g., sera) and thus can be applied to both large and small bat species as well as in longitudinal studies where lethal sampling is necessarily limited. Further, as the serum proteome includes proteins secreted from not only blood cells but also proximal organs, it provides a more general characterization of immune proteins. Here, we expand our recent work on the serum proteome of wild vampire bats (Desmodus rotundus) to better understand CoV pathogenesis. Across 19 bats sampled in 2019 in northern Belize with available sera, we detected CoVs in oral or rectal swabs from four individuals (21.1% positivity). Phylogenetic analyses identified all RdRp gene sequences in vampire bats as novel a-CoVs most closely related to known human CoVs. Across 586 identified serum proteins, we found no strong differences in protein composition nor abundance between uninfected and infected bats. However, receiver operating characteristic curve analyses identified seven to 32 candidate biomarkers of CoV infection, including AHSG, C4A, F12, GPI, DSG2, GSTO1, and RNH1. Enrichment analyses using these protein classifiers identified downregulation of complement, regulation of proteolysis, immune effector processes, and humoral immunity in CoV-infected bats alongside upregulation of neutrophil immunity, overall granulocyte activation, myeloid cell responses, and glutathione processes. Such results denote a mostly cellular immune response of vampire bats to CoV infection and identify putative biomarkers that could provide new insights into CoV pathogenesis in wild and experimental populations. More broadly, applying a similar proteomic approach across diverse bat species and to distinct life history stages in target species could improve our understanding of the immune mechanisms by which wild bats tolerate viruses. [ABSTRACT FROM AUTHOR]