Ecological Immunology Research Articles

Ecological immunology: do sexual attraction and immunity trade-off through a desaturase?

Given the limited availability of resources in nature, sexual attractiveness may trade off with immunocompetence, as the immunocompetence handicap hypothesis (ICHH) posits. In invertebrates, a direct link between trade-offs through hormonal/molecular effectors in sexual signals and immunity has not been found so far. Here, we assessed how variation in sexual signals affected parasite infection in two sex pheromone selected lines of the moth Chloridea virescens: an attractive line with a low ratio of 16:Ald/Z11-16:Ald and an unattractive line with a high ratio. When infecting these lines with an apicomplexan parasite, we found that the attractive Low line was significantly more susceptible to the parasite infection than the unattractive High line. Since the ratio difference between these two lines is determined by a delta-11-desturase, we hypothesized that this desaturase may have a dual role, i.e., in the quality of the sexual signal as well as an involvement in immune response, comparable to testosterone in vertebrates. However, when we used CRISPR/cas9 to knockout delta-11-desturase in the attractive Low line, we found that the pheromonal phenotype did change to that of the High line, but the infection susceptibility did not. Notably, when checking the genomic location of delta-11-desaturase in the C. virescens, we found that mucin is adjacent to delta-11-desaturase. When comparing the mucin sequences in both lines, we found four nonsynonymous SNPs in the coding sequence, as well as intronic variation between the two lines. These differences suggest that genetic hitchhiking may explain the variation in susceptibility to parasitic infection.

The complement system and its involvement in inhibition of Batrachochytriym dendrobatidis, a lethal fungal pathogen of amphibians

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.

Mapping Microbial Selves: Field Notes from a Dirty Parenting Project

Microbes exist everywhere on, in and around us. They are both ubiquitous and largely invisible, at least until they make their presence, or absence, felt. Recent years have seen a heightened sensitivity to microbial threats in the wake of the COVID-19 pandemic and widespread concerns about antimicrobial resistance (AMR) to antibiotics. At the same time, there is also a growing interest in the microbiome as a source of ‘wild immunology’. From this viewpoint, the human body is comprised of, embedded within, and dependent on its exposure to an ecosystem of microbes, and the absence of such exposure is linked to the development of auto-immune conditions such as Crohn’s disease and ulcerative colitis. Inspired by an emerging body of work in the humanities and social sciences which looks to engage with so-called lay knowledge and understandings of microbial forms (including bacteria, viruses, and fungi) and processes (such as contagion or digestion), this Field Note explores the piloting of ‘body mapping’ as a research method to engage with families to explore their collective understanding of their children’s microbiome.

Extracellular vesicles: an emerging tool for wild immunology.

The immune system is crucial for defending organisms against pathogens and maintaining health. Traditionally, research in immunology has relied on laboratory animals to understand how the immune system works. However, there is increasing recognition that wild animals, due to their greater genetic diversity, lifespan, and environmental exposures, have much to contribute to basic and translational immunology. Unfortunately, logistical challenges associated with collecting and storing samples from wildlife, and the lack of commercially available species-specific reagents have hindered the advancement of immunological research on wild species. Extracellular vesicles (EVs) are cell-derived nanoparticles present in all body fluids and tissues of organisms spanning from bacteria to mammals. Human and lab animal studies indicate that EVs are involved in a range of immunological processes, and recent work shows that EVs may play similar roles in diverse wildlife species. Thus, EVs can expand the toolbox available for wild immunology research, helping to overcome some of the challenges associated with this work. In this paper, we explore the potential application of EVs to wild immunology. First, we review current understanding of EV biology across diverse organisms. Next, we discuss key insights into the immune system gained from research on EVs in human and laboratory animal models and highlight emerging evidence from wild species. Finally, we identify research themes in wild immunology that can immediately benefit from the study of EVs and describe practical considerations for using EVs in wildlife research.

Unravelling mechanisms of bacterial recognition by Acanthamoeba: insights into microbial ecology and immune responses.

Acanthamoeba, are ubiquitous eukaryotic microorganisms, that play a pivotal role in recognizing and engulfing various microbes during predation, offering insights into microbial dynamics and immune responses. An intriguing observation lies in the apparent preference of Acanthamoeba for Gram-negative over Gram-positive bacteria, suggesting potential differences in the recognition and response mechanisms to bacterial prey. Here, we comprehensively review pattern recognition receptors (PRRs) and microbe associated molecular patterns (MAMPs) that influence Acanthamoeba interactions with bacteria. We analyze the molecular mechanisms underlying these interactions, and the key finding of this review is that Acanthamoeba exhibits an affinity for bacterial cell surface appendages that are decorated with carbohydrates. Notably, this parallels warm-blooded immune cells, underscoring a conserved evolutionary strategy in microbial recognition. This review aims to serve as a foundation for exploring PRRs and MAMPs. These insights enhance our understanding of ecological and evolutionary dynamics in microbial interactions and shed light on fundamental principles governing immune responses. Leveraging Acanthamoeba as a model organism, provides a bridge between ecological interactions and immunology, offering valuable perspectives for future research.

Immunity and SymBiopolitics

The notion of immunity, as it was defined in biology in the middle of the 20th century, draws a boundary between the “self” and the “nonself”. In this respect the notion of immunity is the perfect metaphor for biopolitical government: similar to the immune system, which fights everything that it sees as “nonself”, biopolitical power discriminates against what it sees as “different” or “other”. However, if we examine immunity not as a metaphor but as a phenomenon viewed from the perspective of contemporary biology, we have to admit that immunity comprises not only a defensive reaction toward an external, contagious element, but also a positive reaction or so-called “tolerance”. Thus, the defensive model of immunity should be complemented by a positive one, interpreting immunity as being entangled in its milieu. Alfred I. Tauber suggested that immunity should be seen as an ecological system which not simply reacts toward the external element but opens the negotiations between the “self” and “nonself” within the system. This model of ecological immunology is also a good methodological tool to rethink the notion of biopolitics: instead of seeing biopolitics as the opposition between a sovereign power and an oppressed individual, we can interpret it as a network of sympoietic interactions between individuals, technologies, and nonhuman others.

Ecoimmunology: What Unconventional Organisms Tell Us after Two Decades.

Model organisms have long been used to characterize the vertebrate immune system, which is responsible for protecting the host from mechanical and pathogen-induced injuries, pathology, and disease development (Janeway et al. 2001). As a result, today we have a deep understanding of how vertebrate defensive responses can be mediated by innate (i.e., non-specific) or adaptive (i.e., specific) mechanisms, or a mixture of both. Innate responses involve a generalized activation of immune mechanisms that can operate in response to any infectious agent (i.e., they are actionable to a diverse range of pathogens and parasites; Pham and Schneider 2008). In contrast, adaptive responses entail an activation of a subset of cells and/or systems to defend a host against a precise pathogen. While many of these mechanisms are highly conserved across vertebrate classes, intriguing distinctions have been revealed by research on non-model organisms (Demas and Nelson 2012). Ecoimmunology, or ecological immunology, emerged as a research area in the late 1990s and early 2000s (Sheldon and Verhulst 1996; Norris and Evans 2000; Zuk and Stoehr 2002; Brock et al. 2014; Downs et al. 2014). In this field, researchers seek to understand the factors leading to variation in the function of the immune system and how this variation contributes to disease susceptibility in a wide variety of taxonomic groups (Sheldon and Verhulst 1996; Norris and Evans 2000; Zuk and Stoehr 2002; Brock et al. 2014; Downs et al. 2014). Since its inception, ecoimmunological studies have predominantly focused on birds, with relatively fewer studies focused on other taxonomic groups (Martin et al. 2003; Ashley et al. 2012; Evans et al. 2015; Haase et al. 2016; Taves et al. 2017; Tieleman 2018). More recently, however, there has been an expansion in the diversity of taxa studied from an ecoimmunological perspective, with studies ranging from plants to invertebrates, ectothermic vertebrates, and non-model (i.e., lab rodents) mammalian species (Rolff and Siva-Jothy 2003; Zimmerman et al. 2010; Ardia et al. 2012; Fisher et al. 2012; Pijanowski et al. 2015; Titon et al. 2019; Sueiro et al. 2020; Zimmerman 2020). In addition, there has been a closer examination and optimization of the immune methods and techniques that are needed to conduct ecoimmunology studies in diverse organisms (e.g., Claunch et al. 2022).

Chemical cues in disease recognition and their immunomodulatory role in insects.

Preventing infections is crucial for host fitness and many insects modify their behaviour upon sensing a contagion. We review chemical cues that mediate insect behaviour in response to parasites, and diseased or dead conspecifics. Considering the large diversity of behavioural disease defences described, surprisingly little is known about disease-associated cues that mediate them, especially their chemoreceptor and neuronal details. Interestingly, disease cues do not only modify host behaviour, but they could also play a direct role in immune system activation via neuroendocrine regulation, bypassing the need for risky immunological contact with the parasite. Such crosstalk is an exciting emerging research area in insect ecological immunology that should prove invaluable in studying host-parasite interactions by combining analytical methods from chemical ecology.

A meta-analysis of impacts of immune response and infection on oxidative status in vertebrates.

Inferring from patterns observed in biomedical research, ecoimmunological theory predicts that oxidative stress is a ubiquitous physiological cost that contributes to generating variation in immune function between individuals or species. This prediction is, however, often challenged by empirical studies testing the relationship between immune response or infection and oxidative status markers. This points out the importance of combining ecological immunology and oxidative stress ecology to further our understanding of the proximate causes and fitness consequences of individual variation in health, and adaptability to natural and anthropogenic environmental changes. I reviewed evidence and performed phylogenetic meta-analyses of changes in oxidative status markers owing to either injection of an antigen or infection in captive and free-living vertebrates (141 studies, 1262 effect sizes, 97 species). The dataset was dominated by studies on fish, birds and mammals, which provided 95.8% of effect sizes. Both antigen injection and parasite exposure were associated with changes of oxidative status. There were significant effects of taxonomic class and experimental environment (captivity vs. wild). In contrast with my predictions, age category (young vs. adult), study design (correlational vs. experimental) and proxies of pace of life (clutch size, litter size, and body mass; for birds and mammals only) were negligible in this dataset. Several methodological aspects (type of immunostimulant, laboratory assay, tissue analysed) showed significant effects on both strength and direction of effect. My results suggest that alterations of oxidative status are a widespread consequence of immune function across vertebrates. However, this work also identified heterogeneity in strength and direction of effect sizes, which suggests that immune function does not necessarily result in oxidative stress. Finally, this work identifies methodological caveats that might be relevant for the interpretation and comparability of results and for the application in conservation programs.

Environmental variability affects optimal trade‐offs in ecological immunology

AbstractThe costs of mounting and maintaining an immune response lead to trade‐offs with investment in (or maintenance of) other organ systems or functions such as reproduction, as has been observed in several taxa, including birds, insects, and mammals. Given these trade‐offs, optimal strategies can be affected by biotic and abiotic conditions; however, how these trade‐offs are affected by environmental variability remains unclear. Using a deterministic within‐host model of disease dynamics, we analyzed the effect of environmental variability (here, the coefficient of variation in the host’s background survival distribution) on the optimal resolution to a trade‐off between investment in reproduction and the immune system. We found that higher variability led to increased investment in the immune system at the cost of decreased early‐life reproduction when the immune investment strategy was assumed to be constant through life. Since we manipulated the distribution of lifespans while keeping the mean lifespan constant, our results suggest that even the small probability of living far past the mean lifespan for individuals in highly variable environments has a large effect on the optimal investment strategy. When immune investment was able to change over the age of the organism, the optimal investment strategies were again contingent on the level of environmental variability experienced by individuals. Our results support and extend previous work on optimal life‐history theory in variable environments by showing that in the context of ecological immunology, the most fit individuals in constant environments are not the most fit individuals in variable environments. The effects of environmental variability on optimal immune investment are likely to have consequences for other aspects of infectious disease such as transmission dynamics, virulence evolution, and the likelihood of epidemics occurring.

Examining adaptive evolution of immune activity: opportunities provided by gastropods in the age of 'omics'.

Parasites threaten all free-living organisms, including molluscs. Understanding the evolution of immune defence traits in natural host populations is crucial for predicting their long-term performance under continuous infection risk. Adaptive trait evolution requires that traits are subject to selection (i.e. contribute to organismal fitness) and that they are heritable. Despite broad interest in the evolutionary ecology of immune activity in animals, the understanding of selection on and evolutionary potential of immune defence traits is far from comprehensive. For instance, empirical observations are only rarely in line with theoretical predictions of immune activity being subject to stabilizing selection. This discrepancy may be because ecoimmunological studies can typically cover only a fraction of the complexity of an animal immune system. Similarly, molecular immunology/immunogenetics studies provide a mechanistic understanding of immunity, but neglect variation that arises from natural genetic differences among individuals and from environmental conditions. Here, we review the current literature on natural selection on and evolutionary potential of immune traits in animals, signal how merging ecological immunology and genomics will strengthen evolutionary ecological research on immunity, and indicate research opportunities for molluscan gastropods for which well-established ecological understanding and/or 'immune-omics' resources are already available. This article is part of the Theo Murphy meeting issue 'Molluscan genomics: broad insights and future directions for a neglected phylum'.

Toxin or medication? Immunotherapeutic effects of nicotine on a specialist caterpillar

Abstract A core tenant in the field of ecological immunology is that immune responses trade off with other physiological functions due to resource allocation costs. Caterpillars, for example, tend to exhibit reduced immune responses when reared on more toxic food plants due to a cost from detoxifying or sequestering secondary metabolites, also known as the ‘vulnerable host hypothesis’. However, support for this hypothesis is mixed, and studies have not yet mechanistically isolated the relative contributions of total plant defences, specific metabolites or macro‐nutritional quality. We used the tobacco hornworm Manduca sexta, a specialist herbivore on plants in the nightshade family (Solanaceae), to investigate trade‐offs in immune response. This system is ideal given the availability of solanaceous plant lines varying in general (i.e. jasmonate‐induced) and specific (i.e. nicotine) resistance traits. We also applied a geometric diet stoichiometry approach to examine how phytochemical toxicity and nutritional quality interactively impact insect immunity and performance. We predicted that as plant toxicity increased, immune activity and herbivore performance would decrease. Increasing food plant toxicity reduced insect growth and development, as predicted, but contrary to our hypothesis, plant toxicity did not trade off with immune parameters. Surprisingly, specific plant chemicals, in this case nicotine, appeared immunotherapeutic, stimulating the phenoloxidase (PO) immune response of M. sexta. Available nutrients in artificial diets, mainly protein, also strongly impacted insect growth, but did not affect PO activity, while diets supplemented with nicotine enhanced the PO and melanization response. This work highlights how specific secondary metabolites, and not overall plant toxicity, impact the immune response. Importantly, our data also suggest an alternative mechanism (i.e. immune enhancement) for reduced parasitoid performance when reared from hosts on toxic plants via tritrophic interactions. A free Plain Language Summary can be found within the Supporting Information of this article.

OneHealth implications of infectious diseases of wild and managed bees

The OneHealth approach aims to further our understanding of the drivers of human, animal and environmental health, and, ultimately, to improve them by combining approaches and knowledge from medicine, biology and fields beyond. Wild and managed bees are essential pollinators of crops and wild flowers. Their health thus directly impacts on human and environmental health. At the same time, these bee species represent highly amenable and relevant model organisms for a OneHealth approach that aims to study fundamental epidemiological questions. In this review, we focus on how infectious diseases of wild and managed bees can be used as a OneHealth model system, informing fundamental questions on ecological immunology and disease transmission, while addressing how this knowledge can be used to tackle the issues facing pollinator health.

Ontogeny of leukocyte profiles in a wild altricial passerine.

Ecophysiological studies have highlighted the relevance of the avian immune system in individual fitness prospects in the wild. However, studies on the ontogeny of avian immunity are scarce. We analyse age-related changes in the cellular constitutive immunity throughout nestling development, as well as its relationship with sex and brood size. We found that cellular constitutive immunity could be affected by age, sex, brood size, or daily rhythm. Early-stage nestlings relied more on cells of the innate immunity rather than on cells linked to the adaptive immune system. Cellular immunity may not be fully mature in fledglings, as reflected by differences in phagocytic cell counts with regard to adults. Beyond the age-dependent effects, agranulocyte cell counts were affected by sibling competition while granulocyte cell counts showed a daily rhythm. We also show that the heterophil to lymphocyte ratio was negatively related to body weight when nestlings become more independent. Our study contributes knowledge to the fields of developmental immunology and ecological immunology based on essential components of the cellular immune system.

Nutritional ecology and ecological immunology in degus: Does early nutrition affect the postnatal development of the immune function?

Environmental conditions experienced by developing animals have an impact on the development and maturity of the immune system. Specifically, the diet experienced during early development influences the maintenance and function of the immune system in young and adult animals. It is well known that exposure to low-protein diets during early development are related to an attenuation of immunocompetence in adulthood. While this functional linkage has been widely studied in altricial models' mammals, it has been little explored how the nutritional history modulates the immune function in precocial animals. We evaluated the effect of dietary protein consumed during early development on the immune function and the oxidative costs in the precocial Caviomorph rodent Octodon degus, or degu. We evaluated components of the acute phase response (APR) and oxidative parameters before and after immune challenge. We found that after the immune challenge, the juveniles on the low-protein dietary treatment exhibited an attenuation of body temperature but showed higher levels of lipid peroxidation than juvenile degus on the high-protein diet. We did not find a significant effect of the interaction between diet and immune challenge on body mass, levels of inflammatory proteins, nor in the total antioxidant capacity. Our results suggest that some components of the immune function and the oxidative status in the degu can be modulated by diet during development. However, the modulation would depend on the immune variables analyzed, and the characteristics of the immune system of precocial rodents.

Microbial environment shapes immune function and cloacal microbiota dynamics in zebra finches Taeniopygia guttata

BackgroundThe relevance of the host microbiota to host ecology and evolution is well acknowledged. However, the effect of the microbial environment on host immune function and host microbiota dynamics is understudied in terrestrial vertebrates. Using a novel experimental approach centered on the manipulation of the microbial environment of zebra finches Taeniopygia guttata, we carried out a study to investigate effects of the host’s microbial environment on: 1) constitutive immune function, 2) the resilience of the host cloacal microbiota; and 3) the degree to which immune function and host microbiota covary in microbial environments that differ in diversity.ResultsWe explored immune indices (hemagglutination, hemolysis, IgY levels and haptoglobin concentration) and host-associated microbiota (diversity and composition) in birds exposed to two experimental microbial environments differing in microbial diversity. According to our expectations, exposure to experimental microbial environments led to differences related to specific antibodies: IgY levels were elevated in the high diversity treatment, whereas we found no effects for the other immune indices. Furthermore, according to predictions, we found significantly increased richness of dominant OTUs for cloacal microbiota of birds of the high diversity compared with the low diversity group. In addition, cloacal microbiota of individual females approached their baseline state sooner in the low diversity environment than females in the high diversity environment. This result supported a direct phenotypically plastic response of host microbiota, and suggests that its resilience depends on environmental microbial diversity. Finally, immune indices and cloacal microbiota composition tend to covary within treatment groups, while at the same time, individuals exhibited consistent differences of immune indices and microbiota characteristics.ConclusionWe show that microbes in the surroundings of terrestrial vertebrates can influence immune function and host-associated microbiota dynamics over relatively short time scales. We suggest that covariation between immune indices and cloacal microbiota, in addition to large and consistent differences among individuals, provides potential for evolutionary adaptation. Ultimately, our study highlights that linking environmental and host microbiotas may help unravelling immunological variation within and potentially among species, and together these efforts will advance the integration of microbial ecology and ecological immunology.

Suppressed LPS-mediated TLR4 signaling in the plateau zokor (Eospalax baileyi) compared to the bamboo rat (Rhizomys pruinosus) and rat (Rattus norvegicus).

Ecological immunology involves the study of the immune function of wildlife, which is seldom compared with that of model animals. Here, we evaluated and compared the level of the innate immune response in the plateau zokor (Eospalax baileyi), an indigenous underground rodent from the Tibetan Plateau, with that in the bamboo rat (Rhizomys pruinosus) and Sprague-Dawley (SD) rat (Rattus norvegicus). The spleen was observed by ordinary light and transmission electron microscopy, and the spleen index was calculated. After liposaccharide (LPS) challenge, the expression of Toll-like receptor 2 (TLR2), TLR4, and hypoxia-inducible factor 1α (HIF-1α) in the spleen was detected by Western blot analysis and immunofluorescence. The expression of nuclear factor-κB1 (NF-κB1) and mitogen-activated protein kinase 14 (MAPK14) in the spleen was detected by real-time quantitative polymerase chain reaction, and the levels of interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and interferon-β (IFN-β) in the spleen were detected by enzyme-linked immunoassay. The spleen index of the plateau zokor was lower than that of the bamboo rat and SD rat. The expression of TLR4, NF-κB1, and MAPK14 and the levels of IL-6 and TNF-α in the spleen of the plateau zokor were lower than those of the bamboo rat and SD rat, while the expression of TLR2 and HIF-1α and the level of IFN-β were higher than those of the bamboo rat and SD rat. We speculate that suppression of the TLR4 signaling pathway in the plateau zokor is an adaptation to hypoxic tunnels that decreases antigenic risk and maintains immune homeostasis. Moreover, the spleen of the plateau zokor is reduced in size, reducing the innate immunity investment in the spleen. We also noted that high levels of HIF-1α in the spleen of the plateau zokor suppressed crosstalk between HIF-1α and TLR4, promoting the innate immune response.

Integrated transcriptomic and functional immunological approach for assessing the invasiveness of bivalve alien species

Biological invasions started when humans moved species beyond their normal geographic limits. Bivalves are the most notoriously invasive species in subtidal aquatic environments. Next-generation sequencing technologies are applied to understand the molecular mechanisms involved in the invasion. The ecological immunology focuses on the role of immunity in invasion, and its magnitude could help to predict the invasiveness of alien species. A remarkable case of invasion has been reported in the Ría de Vigo (Spain) by the black pygmy mussel Xenostrobus securis. In Galicia, the Mediterranean mussel Mytilus galloprovincialis is the predominant cultured bivalve species. Can we predict the invasiveness of alien bivalve species by analyzing their immune response? Can X. securis represent a risk for the autochthonous mussel? We evaluated the suitability of the immune-related hypotheses in our model by using an integrated transcriptomic and functional immunological approach. Our analysis suggests lower immune capabilities in X. securis compared to M. galloprovincialis, probably due to the relocation of energetic resources from the immune response to vital physiological processes to cope with salinity stress. This multidisciplinary approach will help us understand how the immune response can be influenced by the adaptive process and how this immune response can influence the invasion process.

Parasite Load and Site-Specific Parasite Pressure as Determinants of Immune Indices in Two Sympatric Rodent Species.

Simple SummaryWild animals can host diseases that affect humans (i.e., zoonotic diseases). However, not all wild animals are equal in their hosting capacities. In fact, the immune system, the main defense against diseases, varies within and among species. Within species, variation relates to two factors: parasite load and parasite pressure. Parasite load refers to the amount of parasites in or on an individual. Parasite pressure refers to the amount of parasites in a location. The importance of these factors in shaping the immune system of wild rodents, a group of animals known to host zoonotic diseases, is poorly understood. Overall, the rodent species we studied (bank voles and wood mice) hosted 5 microparasites, 9 ectoparasites, and 8 gastrointestinal parasites. We found that parasite load and parasite pressure related to different facets of the immune system. We also found that bank voles exhibited higher levels of one immune defense than wood mice, but higher levels of this defense correlated with a worm infection only in wood mice. Lastly, a white blood cell ratio correlated with infection by a zoonotic parasite. Studies like ours help to document the complexities of host–parasite interactions and how these interactions shape zoonotic disease risk in a changing world.Wildlife is exposed to parasites from the environment. This parasite pressure, which differs among areas, likely shapes the immunological strategies of animals. Individuals differ in the number of parasites they encounter and host, and this parasite load also influences the immune system. The relative impact of parasite pressure vs. parasite load on different host species, particularly those implicated as important reservoirs of zoonotic pathogens, is poorly understood. We captured bank voles (Myodes glareolus) and wood mice (Apodemus sylvaticus) at four sites in the Netherlands. We sampled sub-adult males to quantify their immune function, infestation load for ecto- and gastrointestinal parasites, and infection status for vector-borne microparasites. We then used regression trees to test if variation in immune indices could be explained by among-site differences (parasite pressure), among-individual differences in infestation intensity and infection status (parasite load), or other intrinsic factors. Regression trees revealed splits among sites for haptoglobin, hemagglutination, and body-mass corrected spleen size. We also found splits based on infection/infestation for haptoglobin, hemolysis, and neutrophil to lymphocyte ratio. Furthermore, we found a split between species for hemolysis and splits based on body mass for haptoglobin, hemagglutination, hematocrit, and body-mass corrected spleen size. Our results suggest that both parasite pressure and parasite load influence the immune system of wild rodents. Additional studies linking disease ecology and ecological immunology are needed to understand better the complexities of host–parasite interactions and how these interactions shape zoonotic disease risk.

Integrated transcriptomic and functional immunological approach for assessing the invasiveness of bivalve alien species

Biological invasions started when humans moved species beyond their normal geographic limits. Bivalves are the most notoriously invasive species in subtidal aquatic environments. Next-generation sequencing technologies are applied to understand the molecular mechanisms involved in the invasion. The ecological immunology focuses on the role of immunity in invasion, and its magnitude could help to predict the invasiveness of alien species. A remarkable case of invasion has been reported in the Ria de Vigo (Spain) by the black pygmy mussel Xenostrobus securis. In Galicia, the Mediterranean mussel Mytilus galloprovincialis is the predominant cultured bivalve species. Can we predict the invasiveness of alien bivalve species by analyzing their immune response? Can X. securis represent a risk for the autochthonous mussel? We evaluated the suitability of the immune-related hypotheses in our model by using an integrated transcriptomic and functional immunological approach. Our analysis suggests lower immune capabilities in X. securis compared to M. galloprovincialis, probably due to the relocation of energetic resources from the immune response to vital physiological processes to cope with salinity stress. This multidisciplinary approach will help us understand how the immune response can be influenced by the adaptive process and how this immune response can influence the invasion process.