Principles of ecological immunology

Membership robustness but structural change of the native gut microbiota of bumble bees upon systemic immune induction

Understanding factors influencing the composition and maintenance of beneficial host-associated microbial communities is central to understanding their ecological, evolutionary, and health consequences for hosts. Host immunity is often implicated as a regulator of these microbiota, but immunity may also play a disruptive role, with responses to infection perturbing beneficial communities. Such effects may be more prominent from innate immune responses, with more rapid-acting and often non-specific components, compared to adaptive responses. We investigated how upregulation of antibacterial immunity in the bumble bee Bombus impatiens affects its core gut microbiota, testing the hypothesis that immunity-induced perturbation impacts the microbiota structure. Freshly emerged adult bees were fed a microbiota inoculum before receiving a non-pathogenic immune stimulation injection. We quantified microbial communities using 16S rRNA amplicon sequencing and targeted quantitative PCR. Coarse community membership shows apparent robustness, but we find that immune stimulation alters the abundance of two core community members, Gilliamella and Snodgrassella. Moreover, a positive association in communities between these bacteria is perturbed following a Gram-negative challenge. The observed changes in the gut microbial community are suggestive of immune response-induced dysbiosis, linking ecological interactions across levels between hosts, their pathogens, and their beneficial gut microbiota. The potential for collateral perturbation of the natural gut microbiota following an innate immune response may contribute to immune costs, shaping the evolutionary optimization of immune investment depending on the ecological context.

IMPORTANCE

Our work demonstrates how innate immunity may influence the host-associated microbiota. While previous work has demonstrated the role of adaptive immunity in regulating the microbiota, we show that stimulation of an innate immune response in bumble bees may disrupt the native gut microbial community by shifting individual abundances of some members and pairwise associations. This work builds upon previous work in bumble bees demonstrating factors determining microbe colonization of hosts and microbiota membership, implicating immune response-induced changes as a factor shaping these important gut communities. While some microbiota members appear unaffected, changes in others and the community overall suggests that collateral perturbation of the native gut microbiota upon an innate immune response may serve as an additional selective pressure that shapes the evolution of host innate immunity.

The Interplay of TLR-NFκB Signalling Pathway and Functional Immune-Related Enzymes in the Inflammatory Response of Ciona robusta

The close phylogenetic relationship between ascidians (Tunicata) and vertebrates makes them a powerful model for studying the innate immune system. To better understand the nature and dynamics of immune responses and the mechanisms through which bacterial infections are detected and translated into inflammation in Ciona robusta, we applied an approach combining in vivo lipopolysaccharide (LPS) stimulation, immune-labelling techniques and functional enzymatic analyses. The immunohistochemistry showed that Toll-like receptor 4 (TLR4) and nuclear factor kappa B (NFκB) were expressed during the inflammatory pharynx response 4 h post-LPS, with the formation of nodules in pharynx vessel lumen. Also, the endothelium vessels were involved in the inflammatory response. Observations of histological sections from naive and buffer-inoculated ascidians confirmed an immuno-positive response. Enzyme immune parameters-which included the activity of phenoloxidase, glutathione peroxidase, lysozyme, alkaline phosphatase and esterase-showed up-modulation 4 h after LPS injection, confirming their participation during ascidian inflammatory response. These findings provide new insights into the mechanisms underlying the LPS-induced C. robusta response and suggest that a broad innate immune mechanism, as in vertebrates, is involved in the regulation of inflammatory responses. Further findings in this direction are needed to cover knowledge gaps regarding the organized set of molecular and cellular networks involved in universal immune interactions with pathogens.

Comparative reservoir competence of Peromyscus leucopus, C57BL/6J, and C3H/HeN for Borrelia burgdorferi B31

Borrelia burgdorferi, a Lyme disease spirochete, causes a range of acute and chronic maladies in humans. However, a primary vertebrate reservoir in the United States, the white-footed deermouse Peromyscus leucopus, is reported not to have reduced fitness following infection. Although laboratory strains of Mus musculus mice have successfully been leveraged to model acute human Lyme disease, the ability of these rodents to model B. burgdorferi-P. leucopus interactions remains understudied. Here, we compared infection of P. leucopus with B. burgdorferi B31 with infection of the traditional B. burgdorferi murine models-C57BL/6J and C3H/HeN Mus musculus, which develop signs of inflammation akin to human disease. We find that B. burgdorferi was able to reach much higher burdens (10- to 30-times higher) in multiple M. musculus skin sites and that the overall dynamics of infection differed between the two rodent species. We also found that P. leucopus remained transmissive to larval Ixodes scapularis for a far shorter period than either M. musculus strain. In line with these observations, we found that P. leucopus does launch a modest but sustained inflammatory response against B. burgdorferi in the skin, which we hypothesize leads to reduced bacterial viability and rodent-to-tick transmission in these hosts. Similarly, we also observe evidence of inflammation in infected P. leucopus hearts. These observations provide new insight into reservoir species and the B. burgdorferi enzootic cycle.IMPORTANCEA Lyme disease-causing bacteria, Borrelia burgdorferi, must alternate between infecting a vertebrate host-usually rodents or birds-and ticks. In order to be successful in that endeavor, the bacteria must avoid being killed by the vertebrate host before it can infect a new larval tick. In this work, we examine how B. burgdorferi and one of its primary vertebrate reservoirs, Peromyscus leucopus, interact during an experimental infection. We find that B. burgdorferi appears to colonize its natural host less successfully than conventional laboratory mouse models, which aligns with a sustained seemingly anti-bacterial response by P. leucopus against the microbe. These data enhance our understanding of P. leucopus host-pathogen interactions and could potentially serve as a foundation to uncover ways to disrupt the spread of B. burgdorferi in nature.

Correlated evolution of oxidative physiology and MHC-based immunosurveillance in birds

Maintenance and activation of the immune system incur costs, not only in terms of substrates and energy but also via collateral oxidative damage to host cells or tissues during immune response. So far, associations between immune function and oxidative damage have been primarily investigated at intra-specific scales. Here, we hypothesized that pathogen-driven selection should favour the evolution of effective immunosurveillance mechanisms (e.g. major histocompatibility complex, MHC) and antioxidant defences to mitigate oxidative damage resulting from immune function. Using phylogenetically informed comparative approaches, we provided evidence for the correlated evolution of host oxidative physiology and MHC-based immunosurveillance in birds. Species selected for more robust MHC-based immunosurveillance (higher gene copy numbers and allele diversity) showed stronger antioxidant defences, although selection for MHC diversity still showed a positive evolutionary association with oxidative damage to lipids. Our results indicate that historical pathogen-driven selection for highly duplicated and diverse MHC could have promoted the evolution of efficient antioxidant mechanisms, but these evolutionary solutions may be insufficient to keep oxidative stress at bounds. Although the precise nature of mechanistic links between the MHC and oxidative stress remains unclear, our study suggests that a general evolutionary investment in immune function may require co-adaptations at the level of host oxidative metabolism.

Lysosomal dysfunction by inactivation of V-ATPase drives innate immune response in C. elegans

Pathogens target vacuolar ATPase (V-ATPase) to inhibit lysosomal acidification or lysosomal fusion, causing lysosomal dysfunction. However, it remains unknown whether cells can detect dysfunctional lysosomes and initiate an immune response. In this study, we discover that dysfunction of lysosomes caused by inactivation of V-ATPase enhances innate immunity against bacterial infections. We find that lysosomal V-ATPase interacts with DVE-1, whose nuclear localization serves as a proxy for the induction of mitochondrial unfolded protein response (UPRmt). The inactivation of V-ATPase promotes the nuclear localization of DVE-1, activating UPRmt and inducing downstream immune response genes. Furthermore, pathogen resistance conferred by inactivation of V-ATPase requires dve-1 and its downstream immune effectors. Interestingly, animals grow slower after vha RNAi, suggesting that the vha-RNAi-induced immune response costs the most energy through activation of DVE-1, which trades off with growth. This study reveals how dysfunctional lysosomes can trigger an immune response, emphasizing the importance of conserving energy during immune defense.

Global warming-related response after bacterial challenge in Astroides calycularis, a Mediterranean thermophilic coral

A worldwide increase in the prevalence of coral diseases and mortality has been linked to ocean warming due to changes in coral-associated bacterial communities, pathogen virulence, and immune system function. In the Mediterranean basin, the worrying upward temperature trend has already caused recurrent mass mortality events in recent decades. To evaluate how elevated seawater temperatures affect the immune response of a thermophilic coral species, colonies of Astroides calycularis were exposed to environmental (23 °C) or elevated (28 °C) temperatures, and subsequently challenged with bacterial lipopolysaccharides (LPS). Using immunolabeling with specific antibodies, we detected the production of Toll-like receptor 4 (TLR4) and nuclear factor kappa B (NF-kB), molecules involved in coral immune responses, and heat shock protein 70 (HSP70) activity, involved in general responses to thermal stress. A histological approach allowed us to characterize the tissue sites of activation (epithelium and/or gastroderm) under different experimental conditions. The activity patterns of the examined markers after 6 h of LPS stimulation revealed an up-modulation at environmental temperature. Under warmer conditions plus LPS-challenge, TLR4-NF-kB activation was almost completely suppressed, while constituent elevated values were recorded under thermal stress only. An HSP70 up-regulation appeared in both treatments at elevated temperature, with a significantly higher activation in LPS-challenge colonies. Such an approach is useful for further understanding the molecular pathogen-defense mechanisms in corals in order to disentangle the complex interactive effects on the health of these ecologically relevant organisms related to global climate change.

Pathogenicity analysis and comparative genomics reveal the different infection strategies between the generalist Metarhizium anisopliae and the specialist Metarhizium acridum

BACKGROUND

The fungal genera Metarhizium contain many important multiple species that are used as biocontrol agents and as model organisms for exploring insect-fungal interactions. Metarhizium spp. exhibit different traits of pathogenicity, suggesting that the pathogenesis can be quite distinctive. However, the underlying differences in their pathogenesis remain poorly understood.

RESULTS

Pathogenicity analysis showed that Metarhizium anisopliae (strain CQMa421) displayed higher virulence against oriental migratory locusts, Locusta migratoria manilensis (Meyen), than the acridid-specific specie Metarhizium acridum (strain CQMa102). Relative to M. acridum, M. anisopliae possessed a higher conidial hydrophobicity, increased ability to penetrate the host, accelerated growth under hypoxia and enhanced ability for the utilization of different carbon sources. Different distributions of carbohydrate epitopes at cell wall surface of M. anisopliae might also contribute to successful evasion of host immune defenses. Comparative genomics showed that M. anisopliae has 98 more virulence-related secreted proteins (133) than M. acridum (35), which can be functionally classified as hydrolases, virulence effectors, cell wall degradation and stress tolerance-related proteins, and helpful to the cuticle penetration and host internal environment adaption. In addition, differences in genomic clusters specifically related to secondary metabolites, including the clusters of Indole-NRPS hybrid, T1PKS-NRPS like hybrid, Betalactone, Fungal-Ripp and NRPS-Terpene hybrid, may lead to differences in core virulence-related secondary metabolite genes in M. acridum (18) and M. anisopliae (36).

CONCLUSION

The comparative study provided new insights into the different infection strategies between M. anisopliae and M. acridum, and further facilitate the identification of virulence-related genes for the improvement of mycoinsecticides. © 2023 Society of Chemical Industry.

Activation of immune defences against parasitoid wasps does not underlie the cost of infection

Parasites reduce the fitness of their hosts, and different causes of this damage have fundamentally different consequences for the evolution of immune defences. Damage to the host may result from the parasite directly harming its host, often due to the production of virulence factors that manipulate host physiology. Alternatively, the host may be harmed by the activation of its own immune defences, as these can be energetically demanding or cause self-harm. A well-studied model of the cost of infection is Drosophila melanogaster and its common natural enemy, parasitoid wasps. Infected Drosophila larvae rely on humoral and cellular immune mechanisms to form a capsule around the parasitoid egg and kill it. Infection results in a developmental delay and reduced adult body size. To disentangle the effects of virulence factors and immune defences on these costs, we artificially activated anti-parasitoid immune defences in the absence of virulence factors. Despite immune activation triggering extensive differentiation and proliferation of immune cells together with hyperglycaemia, it did not result in a developmental delay or reduced body size. We conclude that the costs of infection do not result from these aspects of the immune response and may instead result from the parasite directly damaging the host.

Investigating the influence of diet diversity on infection outcomes in a bumble bee (Bombus impatiens) and microsporidian (Nosema bombi) host-pathogen system

Diet can have an array of both direct and indirect effects on an organism's health and fitness, which can influence the outcomes of host-pathogen interactions. Land use changes, which could impact diet quantity and quality, have imposed foraging stress on important natural and agricultural pollinators. Diet related stress could exacerbate existing negative impacts of pathogen infection. Accounting for most of its nutritional intake in terms of protein and many micronutrients, pollen can influence bee health through changes in immunity, infection, and various aspects of individual and colony fitness. We investigate how adult pollen consumption, pollen type, and pollen diversity influence bumble bee Bombus impatiens survival and infection outcomes for a microsporidian pathogen Nosema (Vairimorpha) bombi. Experimental pathogen exposures of larvae occurred in microcolonies and newly emerged adult workers were given one of three predominantly monofloral, polyfloral, or no pollen diets. Workers were assessed for size, pollen consumption, infection 8-days following adult-eclosion, survival, and the presence of extracellular microsporidian spores at death. Pollen diet treatment, specifically absence of pollen, and infection independently reduced survival, but we saw no effects of pollen, pollen type, or pollen diet diversity on infection outcomes. The latter suggests infection outcomes were likely already set, prior to differential diets. Although infection outcomes were not altered by pollen diet in our study, it highlights both pathogen infection and pollen availability as important for bumble bee health, and these factors may interact at different stages of bumble bee development, at the colony level, or under different dietary regimes.

Trans-generational immune priming is not mediated by the sex of the parent primed: a meta-analysis of invertebrate data

Traditionally, only vertebrates were thought capable of acquired immune responses, such as the ability to transfer immunological experience vertically to their offspring (known as trans-generational immune priming, TGIP). Increasing evidence challenges this belief and it is now clear that invertebrates also have the ability to exhibit functionally equivalent TGIP. This has led to a surge in papers exploring invertebrate TGIP, with most focusing on the costs, benefits or factors that affect the evolution of this trait. Whilst many studies have found support for the phenomenon, not all studies do, and there is considerable variation in the strength of positive results. To address this, we conducted a meta-analysis to answer the question: what is the overall effect of TGIP in invertebrates? Then, to understand the specific factors that affect its presence and intensity, we conducted a moderator analysis. Our results corroborate that TGIP occurs in invertebrates (demonstrated by a large, positive effect size). The strength of the positive effect was related to if and how offspring were immune challenged (i.e. whether they were challenged with the same or different insult as their parents or not challenged at all). Interestingly, there was no effect of the ecology or life history of the species or the sex of the parent or the offspring primed, and responses were comparable across different immune elicitors. Our publication bias testing suggests that the literature may suffer from some level of positive-result bias. However, even after accounting for potential bias, our effect size remains positive. Publication bias testing can be influenced by diversity in the data set, which was considerable in our data, even after moderator analysis. It is therefore conceivable that differences among studies could be caused by other moderators that were unable to be included in our meta-analysis. Nonetheless, our results suggest that TGIP does occur in invertebrates, whilst providing some potential avenues to examine the factors that account for variation in effect sizes.

Consequences of microsporidian prior exposure for virus infection outcomes and bumble bee host health

Host-parasite interactions do not occur in a vacuum, but in connected multi-parasite networks that can result in co-exposures and coinfections of individual hosts. These can affect host health and disease ecology, including disease outbreaks. However, many host-parasite studies examine pairwise interactions, meaning we still lack a general understanding of the influence of co-exposures and coinfections. Using the bumble bee Bombus impatiens, we study the effects of larval exposure to a microsporidian Nosema bombi, implicated in bumble bee declines, and adult exposure to Israeli Acute Paralysis Virus (IAPV), an emerging infectious disease from honey bee parasite spillover. We hypothesize that infection outcomes will be modified by co-exposure or coinfection. Nosema bombi is a potentially severe, larval-infecting parasite, and we predict that prior exposure will result in decreased host resistance to adult IAPV infection. We predict double parasite exposure will also reduce host tolerance of infection, as measured by host survival. Although our larval Nosema exposure mostly did not result in viable infections, it partially reduced resistance to adult IAPV infection. Nosema exposure also negatively affected survival, potentially due to a cost of immunity in resisting the exposure. There was a significant negative effect of IAPV exposure on survivorship, but prior Nosema exposure did not alter this survival outcome, suggesting increased tolerance given the higher IAPV infections in the bees previously exposed to Nosema. These results again demonstrate that infection outcomes can be non-independent when multiple parasites are present, even when exposure to one parasite does not result in a substantial infection.

Programmed and environmental determinants driving neonatal mucosal immune development

The mucosal immune system of neonates goes through successive, non-redundant phases that support the developmental needs of the infant and ultimately establish immune homeostasis. These phases are informed by environmental cues, including dietary and microbial stimuli, but also evolutionary developmental programming that functions independently of external stimuli. The immune response to exogenous stimuli is tightly regulated during early life; thresholds are set within this neonatal "window of opportunity" that govern how the immune system will respond to diet, the microbiota, and pathogenic microorganisms in the future. Thus, changes in early-life exposure, such as breastfeeding or environmental and microbial stimuli, influence immunological and metabolic homeostasis and the risk of developing diseases such as asthma/allergy and obesity.

Fish vulnerability to capture by trapping is modulated by individual parasite density

Commercial fishery harvest is a powerful evolutionary agent, but we know little about whether environmental stressors affect harvest-associated selection. We test how parasite infection relates to trapping vulnerability through selective processes underlying capture. We used fish naturally infected with parasites, including trematodes causing black spots under fish skin. We first assessed how individual parasite density related to standard metabolic rate (SMR), maximum metabolic rate (MMR) and absolute aerobic scope (AAS)-then used laboratory fishing simulations to test how capture vulnerability was related to parasite density. We further explored group-trapping dynamics using experimental shoals containing varying proportions of infected fish (groups of six with either 0, 2, 4 or 6 infected individuals). At the individual level, we found a positive relationship between parasite presence and SMR, but not MMR or AAS. While we saw no relationship between individual metabolic capacity and vulnerability to trapping, we found the length of time fish spent in traps increased with increasing parasite density, a predictor of trapping-related capture probability. At the group level, the number of infected individuals in a shoal did not affect overall group trapping vulnerability. Our results suggest that parasite infection has some capacity to shift individual vulnerability patterns in fisheries, and potentially influence the evolutionary outcomes of fisheries-induced evolution.

Genomic architecture and sexually dimorphic expression underlying immunity in the red mason bee, Osmia bicornis

Insect pollinators provide crucial ecosystem services yet face increasing environmental pressures. The challenges posed by novel and reemerging pathogens on bee health means we need to improve our understanding of the immune system, an important barrier to infections and disease. Despite the importance of solitary bees, which are ecologically relevant, our understanding of the genomic basis and molecular mechanisms underlying their immune potential, and how intrinsic and extrinsic factors may influence it is limited. To improve our understanding of the genomic architecture underlying immunity of a key solitary bee pollinator, we characterized putative immune genes of the red mason bee, Osmia bicornis. In addition, we used publicly available RNA-seq datasets to determine how sexes differ in immune gene expression and splicing but also how pesticide exposure may affect immune gene expression in females. Through comparative genomics, we reveal an evolutionarily conserved set of more than 500 putative immune-related genes. We found genome-wide patterns of sex-biased gene expression, with greater enrichment of immune-related processes among genes with higher constitutive expression in males than females. Our results also suggest an up-regulation of immune-related genes in response to exposure to two common neonicotinoids, thiacloprid and imidacloprid. Collectively, our study provides important insights into the gene repertoire, regulation and expression differences in the sexes of O. bicornis, as well as providing additional support for how neonicotinoids can affect immune gene expression, which may affect the capacity of solitary bees to respond to pathogenic threats.

Coral growth anomalies, neoplasms, and tumors in the Anthropocene

One of the most widespread coral diseases linked to anthropogenic activities and recorded on reefs worldwide is characterized by anomalous growth formations in stony corals, referred to as coral growth anomalies (GAs). The biological functions of GA tissue include limited reproduction, reduced access to resources, and weakened ability to defend against predators. Transcriptomic analyses have revealed that, in some cases, disease progression can involve host genes related to oncogenesis, suggesting that the GA tissues may be malignant neoplasms such as those developed by vertebrates. The number of studies reporting the presence of GAs in common reef-forming species highlights the urgency of a thorough understanding of the pathology and causative factors of this disease and its parallels to higher organism malignant tissue growth. Here, we review the current state of knowledge on the etiology and holobiont features of GAs in reef-building corals.

Variation in symbiont density is linked to changes in constitutive immunity in the facultatively symbiotic coral, Astrangia poculata

Scleractinian corals are essential ecosystem engineers, forming the basis of coral reef ecosystems. However, these organisms are in decline globally, in part due to rising disease prevalence. Most corals are dependent on symbiotic interactions with single-celled algae from the family Symbiodiniaceae to meet their nutritional needs, however, suppression of host immunity may be essential to this relationship. To explore immunological consequences of algal symbioses in scleractinian corals, we investigated constitutive immune activity in the facultatively symbiotic coral, Astrangia poculata. We compared immune metrics (melanin synthesis, antioxidant production and antibacterial activity) between coral colonies of varying symbiont density. Symbiont density was positively correlated to both antioxidant activity and melanin concentration, likely as a result of the dual roles of these pathways in immunity and symbiosis regulation. Our results confirm the complex nature of relationships between algal symbiosis and host immunity and highlight the need for nuanced approaches when considering these relationships.

Sustained Inflammation Induced by LPS Leads to Tolerable Anorexia and Fat Loss via Tlr4 in Mice

Background

Sustained inflammation is implicated in a variety of pathological conditions like infection, obesity and type 2 diabetes. Lipid metabolism is crucial to support immune response during infection of bacteria. However, how sustained inflammation affects lipid metabolism, especially in white adipose tissue remains largely unknown.

Methods

Sustained inflammation was induced by daily injection of Lipopolysaccharide (LPS). Tlr4 knockout mice were used to study the mechanism. Inflammation and lipid metabolism were evaluated by quantitative PCR, white blood cell counting, nuclear magnetic resonance, fat cell size quantification, lipolysis and fatty acid uptake assays, respiratory exchange ratio, and energy expenditure.

Results

Here, we found that sustained inflammation leads to fat loss in mice with a quick loss and gradual increase manner. Moreover, LPS injection leads to inflammation, anorexia, decreased lipid anabolism, and increased lipid catabolism. Mechanically, we show that LPS induces fat loss, inflammation, anorexia, and alteration of lipid metabolism mainly dependent on Tlr4. Interestingly, sustained inflammation induces less fat loss, especially in epididymal white adipose tissue, than pair-feeding, and pair-feeding has no significant effect on inflammation and leads to less fatty acid uptake, more lipid catabolism and energy expenditure than LPS injection. In addition, we demonstrate that short-term sustained inflammation leads to relative long-term tolerance for LPS-induced anorexia, inflammation and altered lipid metabolism.

Conclusion

These findings demonstrate that sustained inflammation induced by LPS leads to tolerable anorexia and fat loss via Tlr4 in mice, and provide new insights into the effect of sustained inflammation on lipid metabolism and subsequent tolerance.

Fluctuating Starvation Conditions Modify Host-Symbiont Relationship Between a Leaf Beetle and Its Newly Identified Gregarine Species

Gregarines are ubiquitous endosymbionts in invertebrates, including terrestrial insects. However, the biodiversity of gregarines is probably vastly underestimated and the knowledge about their role in shaping fitness-related traits of their host in dependence of fluctuating environmental conditions is limited. Using morphological and molecular analyses, we identified a new gregarine species, Gregarina cochlearium sp. n., in the mustard leaf beetle, Phaedon cochleariae. Applying a full-factorial design, we investigated the effects of a gregarine infection in combination with fluctuating starvation conditions during the larval stage on the development time and fitness-related traits of adult beetles. Under benign environmental conditions, the relationship between gregarines and the host seemed neutral, as host development, body mass, reproduction and survival were not altered by a gregarine infection. However, when additionally exposed to starvation, the combination of gregarine infection and this stress resulted in the lowest reproduction and survival of the host, which points to a parasitic relationship. Furthermore, when the host experienced starvation, the development time was prolonged and the adult females were lighter compared to non-starved individuals, independent of the presence of gregarines. Counting of gregarines in the guts of larvae revealed a lower gregarine load with increasing host body mass under stable food conditions, which indicates a regulation of the gregarine burden in dependence of the host condition. Contrary, in starved individuals the number of gregarines was the highest, hence the already weakened host suffered additionally from a higher gregarine burden. This interactive effect between gregarine infection and fluctuating starvation conditions led to an overall reduced fitness of P. cochleariae. Our study emphasizes the need to study endosymbionts as important components of the natural environment and to investigate the role of host-symbiont relationships under fluctuating environmental conditions in an evolutionary and ecological context.

Effects of Thiamethoxam-Dressed Oilseed Rape Seeds and Nosema ceranae on Colonies of Apis mellifera iberiensis, L. under Field Conditions of Central Spain. Is Hormesis Playing a Role?

Simple Summary

The collapse of the honey bee colonies is a complex phenomenon in which different factors may participate in an interrelated manner (e.g., pathogen interactions, exposure to chemicals, beekeeping practices, climatology, etc.). In light of the current debate regarding the interpretation of field and monitoring studies in prospective risk assessments, here we studied how exposure to thiamethoxam affects honey bee colonies in Central Spain when applied as a seed treatment to winter oilseed rape, according to the good agricultural practice in place prior to the EU restrictions. Under the experimental conditions, exposure to thiamethoxam, alone or in combination with other stressors, did not generate and maintain sufficient chronic stress as to provoke honey bee colony collapse. The stress derived from exposure to thiamethoxam and honey bee pathogens was compensated by adjustments in the colony’s dynamics, and by an increase in the worker bee population, a behavior known as hormesis. An analysis of the factors underlying this phenomenon should be incorporated into the prospective risk assessment of plant protection products in order to improve the future interpretation of field studies and management practices.

Abstract

To study the influence of thiamethoxam exposure on colony strength and pathogen prevalence, an apiary (5 colonies) was placed in front of a plot sown with winter oilseed rape (wOSR), just before the flowering phase. Before sowing, the seeds were treated with an equivalent application of 18 g thiamethoxam/ha. For comparison, a second apiary (5 colonies) was located in front of a separate 750 m plot sown with untreated wOSR. Dead foragers at the entrance of hives were assessed every 2–3 days throughout the exposure period, while the colony strength (number of combs covered with adult honey bees and brood) and pathogens were monitored each month until the following spring. Foraging on the wOSR crop was confirmed by melissopalynology determination of the corbicular pollen collected periodically, while the chemical analysis showed that exposure to thiamethoxam was mainly through nectar. There was an increase in the accumulation of dead bees in the apiary exposed to thiamethoxam relating with the control, which was coped with an increment of bee brood surface and adult bee population. However, we did not find statistically significant differences between apiaries (α = 0.05) in terms of the evolution of pathogens. We discuss these results under hormesis perspective.

Control of immunity via nutritional interventions

Nutrition affects all physiological processes including those linked to the development and function of our immune system. Here, we discuss recent evidence and emerging concepts supporting the idea that our newfound relationship with nutrition in industrialized countries has fundamentally altered the way in which our immune system is wired. This will be examined through the lens of studies showing that mild or transient reductions in dietary intake can enhance protective immunity while also limiting aberrant inflammatory responses. We will further discuss how trade-offs and priorities begin to emerge in the context of severe nutritional stress. In those settings, specific immunological functions are heightened to re-enforce processes and tissue sites most critical to survival. Altogether, these examples will emphasize the profound influence nutrition has over the immune system and highlight how a mechanistic exploration of this cross talk could ultimately lead to the design of novel therapeutic approaches that prevent and treat disease.

Defensive Symbionts and the Evolution of Parasitoid Host Specialization

Insect host-parasitoid interactions abound in nature and are characterized by a high degree of host specialization. In addition to their behavioral and immune defenses, many host species rely on heritable bacterial endosymbionts for defense against parasitoids. Studies on aphids and flies show that resistance conferred by symbionts can be very strong and highly specific, possibly as a result of variation in symbiont-produced toxins. I argue that defensive symbionts are therefore an important source of diversifying selection, promoting the evolution of host specialization by parasitoids. This is likely to affect the structure of host-parasitoid food webs. I consider potential changes in terms of food web complexity, although the nature of these effects will also be influenced by whether maternally transmitted symbionts have some capacity for lateral transfer. This is discussed in the light of available evidence for horizontal transmission routes. Finally, I propose that defensive mutualisms other than microbial endosymbionts may also exert diversifying selection on insect parasitoids.

No Evidence for Constitutive Innate Immune Senescence in a Longitudinal Study of a Wild Bird

AbstractAging is associated with declines in physiological performance; declining immune defenses particularly could have consequences for age-related fitness and survival. In aging vertebrates, adaptive (memory-based) immune responses typically become impaired, innate (nonspecific) responses undergo lesser declines, and inflammation increases. Longitudinal studies of immune functions in wild animals are rare, yet they are needed to understand immunosenescence under evolutionarily relevant conditions. Using longitudinal data from a tropical passerine (Malurus coronatus) population, we investigate how population trends emerge from within-individual changes and between-individual heterogeneity (e.g., selective disappearance) in immune status. We quantified constitutive immune indexes (haptoglobin [inflammation associated], natural antibodies, complement [lytic] activity, and heterophil-lymphocyte ratio; n=505-631) in individuals sampled one to seven times over 5 yr. Unexpectedly, longitudinal analyses showed no age-related change within individuals in any immune index, despite sufficient power to detect within-individual change. Between individuals, we found age-related declines in natural antibodies and increases in heterophil-lymphocyte ratios. However, selective disappearance could not adequately explain between-individual age effects, and longitudinal models could not explain our data better than cross-sectional analyses. The lack of clear within-individual immunosenescence is itself notable. Persistent levels of haptoglobin, complement activity, and natural antibodies into old age suggests that these immune components are maintained, potentially with adaptive significance.

Ineffective humoral anti-tick IgY-response in birds: reaction against pathogen constituents?

Background: Variation in parasite burdens among hosts is typically related to differences in adaptive immunity. Comprehension of underlying mechanisms is hence necessary to gain better insights into endemic transmission cycles. Here we investigate whether wild songbirds that have never been exposed to ticks develop adaptive humoral immunity against endemic Ixodes ricinus ticks. Methods: Blue tits were exposed three times in succession to wild Ixodes ricinus ticks. For each infestation, serum samples were obtained. An enzyme-linked immunosorbent assay was developed, using tick salivary antigens, in order to quantify the bird's IgY response against ticks. In addition, at every sampling occasion the birds' body weight (corrected for body size) and haematocrit level was determined. Results: Individual IgY levels against the ticks' salivary proteins increased over three consecutive tick infestations, and large among-individual variation was observed. The responses were specifically directed against I. ricinus; cross-reactivity against the congeneric tree-hole tick Ixodes arboricola was negligibly low. IgY responses did not impinge on tick feeding success (engorgement weight and attachment success). Yet, those birds with the highest immune responses were more capable to reduce the acute harm (blood depletions) by compensating erythrocyte loss. Furthermore, at the end of the experiment, these birds had gained more body weight than birds with lower IgY levels. Conclusions: Latter observations can be considered as an effect of host quality and/or tolerance mechanisms. Birds anticipate the (future) costs of the activation of the immune system by ticks and/or ongoing tick-borne pathogen infections. Furthermore, although unsuccessful against tick feeding, the IgY responses may indirectly protect birds against tick-borne disease by acting against salivary protein secretions on which pathogens rely for transmission.

Pathogens Spillover from Honey Bees to Other Arthropods

Honey bees, and pollinators in general, play a major role in the health of ecosystems. There is a consensus about the steady decrease in pollinator populations, which raises global ecological concern. Several drivers are implicated in this threat. Among them, honey bee pathogens are transmitted to other arthropods populations, including wild and managed pollinators. The western honey bee, Apis mellifera, is quasi-globally spread. This successful species acted as and, in some cases, became a maintenance host for pathogens. This systematic review collects and summarizes spillover cases having in common Apis mellifera as the mainteinance host and some of its pathogens. The reports are grouped by final host species and condition, year, and geographic area of detection and the co-occurrence in the same host. A total of eighty-one articles in the time frame 1960-2021 were included. The reported spillover cases cover a wide range of hymenopteran host species, generally living in close contact with or sharing the same environmental resources as the honey bees. They also involve non-hymenopteran arthropods, like spiders and roaches, which are either likely or unlikely to live in close proximity to honey bees. Specific studies should consider host-dependent pathogen modifications and effects on involved host species. Both the plasticity of bee pathogens and the ecological consequences of spillover suggest a holistic approach to bee health and the implementation of a One Health approach.

The effects of host plant species and larval density on immune function in the polyphagous moth Spodoptera littoralis

Immune functions are costly, and immune investment is usually dependent on the individual's condition and resource availability. For phytophagous insects, host plant quality has large effects on performance, for example growth and survival, and may also affect their immune function. Polyphagous insects often experience a large variation in quality among different host plant species, and their immune investment may thus vary depending on which host plant species they develop on. Larvae of the polyphagous moth Spodoptera littoralis have previously been found to exhibit density-dependent prophylaxis as they invest more in certain immune responses in high population densities. In addition, the immune response of S. littoralis has been shown to depend on nutrient quality in experiments with artificial diet. Here, I studied the effects of natural host plant diet and larval density on a number of immune responses to understand how host plant species affects immune investment in generalist insects, and whether the density-dependent prophylaxis could be mediated by host plant species. While host plant species in general did not mediate the density-dependent immune expression, particular host plant species was found to increase larval investment in certain functions of the immune system. Interestingly, these results indicate that different host plants may provide a polyphagous species with protection against different kinds of antagonisms. This insight may contribute to our understanding of the relationship between preference and performance in generalists, as well as having applied consequences for sustainable pest management.

Consequences of combining sex-specific traits

Males and females follow distinct life-history strategies that have co-evolved with several sex-specific traits. Higher investment into parental investment (PI) demands an increased lifespan. Thus, resource allocation toward an efficient immune system is mandatory. In contrast, resources allocated toward secondary sexual signals (ornamentation) may negatively correlate with investment into immunity and ultimately result in a shorter lifespan. Previous studies have addressed how resource allocation toward single sex-specific traits impacts lifetime reproductive success (LRS). However, the trade-offs between diverse sex-specific characteristics and their impact on LRS remain largely unassessed impeding our understanding of life-history evolution. We have designed a theoretical framework (informed by experimental data and evolutionary genetics) that explores the effects of multiple sex-specific traits and assessed how they influence LRS. From the individual sex-specific traits, we inferred the consequences at the population level by evaluating adult sex ratios (ASR). Our theory implies that sex-specific resource allocation toward the assessed traits resulted in a biased ASR. Our model focuses on the impact of PI, ornamentation, and immunity as causal to biased ASR. The framework developed herein can be employed to understand the combined impact of diverse sex-specific traits on the LRS and the eventual population dynamics of particular model systems.

Pendimethalin-based herbicide impairs cellular immune response and haemocyte morphology in a beneficial ground beetle

Herbicides have become the most commonly applied agrochemicals in agroecosystems. Thus, basic knowledge of their physiological effects on insects is needed, especially for understanding their impact on beneficial insect species. In this study, we evaluated the effect of a pendimethalin-based herbicide (PND) on the cellular immune response of the carabid beetle Harpalus (Pseudoophonus) rufipes (De Geer 1774) (Coleoptera, Carabidae), acting as biocontrol agent in agroecosystems. Total and differential haemocyte counts and phagocytosis assay, performed by injecting in vivo carboxylate-modified polystyrene latex beads, were measured in beetles exposed to a recommended field dose (4L per ha) of PND to evaluate the exposure effects over the time. The pattern of haemocyte subpopulations and the decrease of the phagocytic index after the exposure to PND suggested a lowering of P. rufipes ability to face an infection performing a cell-mediated response. PND was also found to cause cytotoxic effects on the haemocyte ultrastructure. Ultrastructural alterations such as irregular shape, large vacuolization of the cytoplasm, and condensation of marginated chromatin were recorded from 2d of exposure. The loss of RER, Golgi apparatus, mitochondria integrity and the swelling of the outer nuclear membrane found in some haemocytes suggested an interference of PND with the membrane permeability. Results indicated that the exposure to PND impairs the distribution, morphology and physiological functions of haemocytes causing a decrease of P. rufipes immunocompetence. Moreover, the sensitivity to herbicide exposure makes this species a suitable model and a useful bioindicator for monitoring exposure effects on non-target species. This study provides useful information to protect and preserve biodiversity of insects in agroecosystems.

Urinary neopterin of wild chimpanzees indicates that cell-mediated immune activity varies by age, sex, and female reproductive status

The study of free-living animal populations is necessary to understand life history trade-offs associated with immune investment. To investigate the role of life history strategies in shaping proinflammatory cell-mediated immune function, we analyzed age, sex, and reproductive status as predictors of urinary neopterin in 70 sexually mature chimpanzees (Pan troglodytes) at Ngogo, Kibale National Park, Uganda. In the absence of clinical signs of acute infectious disease, neopterin levels significantly increased with age in both male and female chimpanzees, as observed in humans and several other vertebrate species. Furthermore, males exhibited higher neopterin levels than females across adulthood. Finally, females with full sexual swellings, pregnant females, and post-reproductive females, the oldest individuals in our sample, exhibited higher neopterin levels than lactating females and cycling females without full swellings. Variation in females' neopterin levels by reproductive status is consistent with post-ovulatory and pregnancy-related immune patterns documented in humans. Together, our results provide evidence of ample variation in chimpanzee immune activity corresponding to biodemographic and physiological variation. Future studies comparing immune activity across ecological conditions and social systems are essential for understanding the life histories of primates and other mammals.

Testing the multiple stressor hypothesis: chlorothalonil exposure alters transmission potential of a bumblebee pathogen but not individual host health

Numerous threats are putting pollinator health and essential ecosystem pollination services in jeopardy. Although individual threats are widely studied, their co-occurrence may exacerbate negative effects, as posited by the multiple stressor hypothesis. A prominent branch of this hypothesis concerns pesticide-pathogen co-exposure. A landscape analysis demonstrated a positive association between local chlorothalonil fungicide use and microsporidian pathogen (Nosema bombi) prevalence in declining bumblebee species (Bombus spp.), suggesting an interaction deserving further investigation. We tested the multiple stressor hypothesis with field-realistic chlorothalonil and N. bombi exposures in worker-produced B. impatiens microcolonies. Chlorothalonil was not avoided in preference assays, setting the stage for pesticide-pathogen co-exposure. However, contrary to the multiple stressor hypothesis, co-exposure did not affect survival. Bees showed surprising tolerance to Nosema infection, which was also unaffected by chlorothalonil exposure. However, previously fungicide-exposed infected bees carried more transmission-ready spores. Our use of a non-declining bumblebee and potential higher chlorothalonil exposures under some scenarios could mean stronger individual or interactive effects in certain field settings. Yet, our results alone suggest consequences of pesticide co-exposure for pathogen dynamics in host communities. This underlies the importance of considering both within- and between-host processes when addressing the multiple stressor hypothesis in relation to pathogens.

Epigenetic potential affects immune gene expression in house sparrows

Epigenetic mechanisms may play a central role in mediating phenotypic plasticity, especially during range expansions, when populations face a suite of novel environmental conditions. Individuals may differ in their epigenetic potential (EP; their capacity for epigenetic modifications of gene expression), which may affect their ability to colonize new areas. One form of EP, the number of CpG sites, is higher in introduced house sparrows (Passer domesticus) than in native birds in the promoter region of a microbial surveillance gene, Toll-like Receptor 4 (TLR4), which may allow invading birds to fine-tune their immune responses to unfamiliar parasites. Here, we compared TLR4 gene expression from whole blood, liver and spleen in house sparrows with different EP, first challenging some birds with lipopolysaccharide (LPS), to increase gene expression by simulating a natural infection. We expected that high EP would predict high inducibility and reversibility of TLR4 expression in the blood of birds treated with LPS, but we did not make directional predictions regarding organs, as we could not repeatedly sample these tissues. We found that EP was predictive of TLR4 expression in all tissues. Birds with high EP expressed more TLR4 in the blood than individuals with low EP, regardless of treatment with LPS. Only females with high EP exhibited reversibility in gene expression. Further, the effect of EP varied between sexes and among tissues. Together, these data support EP as one regulator of TLR4 expression.

Transformation of glycerate kinase (GLYK) into Metarhizium acridum increases virulence to locust

BACKGROUND

Improvements in the virulence of the fungal pathogen Metarhizium acridum can crucially promote its efficacy to control locusts and grasshoppers. The polysaccharide components of the cell wall remarkably contribute to fungal virulence.

RESULTS

Here we found that M. acridum lacked the gene families of glycerate-3-kinase (GLYK) as the synthesis enzymes of saccharides. We then generated mutants by introducing the GLYK gene from the host-generalist M. robertsii into the host-specialist M. acridum. Consequently, compared with the wild-type strain, the mutant strain (Ma::MrGLYK) increased the level of phospho-6-fructose in mycelia, the length and density of the mannan fibril layer on the cell wall. The mutant strains increased the mannan fibril in the cell wall and resistance to heat stress. Further transcriptome analysis showed that compared with the wild-type strain, topical infection of Ma::MrGLYK strain induced higher expression of genes such as pattern-recognition proteins, serine protease, and CYP450s in locusts, while reduced the expression of antimicrobial peptide and phenoloxidase activity. Moreover, topical infection and injection of Ma::MrGLYK significantly increased the mortality and shortened the lifespan of locusts compared with wild-type M. acridum.

CONCLUSION

Our study highlighted the application potential of the novel genetically modified fungal mutant of the host-specialist M. acridum as a biocontrol agent against locust plagues. © 2020 Society of Chemical Industry.

Evolution and Expression of the Immune System of a Facultatively Anadromous Salmonid

Vertebrates have evolved a complex immune system required for the identification of and coordinated response to harmful pathogens. Migratory species spend periods of their life-cycle in more than one environment, and their immune system consequently faces a greater diversity of pathogens residing in different environments. In facultatively anadromous salmonids, individuals may spend parts of their life-cycle in freshwater and marine environments. For species such as the brown trout Salmo trutta, sexes differ in their life-histories with females more likely to migrate to sea while males are more likely to stay and complete their life-cycle in their natal river. Salmonids have also undergone a lineage-specific whole genome duplication event, which may provide novel immune innovations but our current understanding of the differences in salmonid immune expression between the sexes is limited. We characterized the brown trout immune gene repertoire, identifying a number of canonical immune genes in non-salmonid teleosts to be duplicated in S. trutta, with genes involved in innate and adaptive immunity. Through genome-wide transcriptional profiling (“RNA-seq”) of male and female livers to investigate sex differences in gene expression amplitude and alternative splicing, we identified immune genes as being generally male-biased in expression. Our study provides important insights into the evolutionary consequences of whole genome duplication events on the salmonid immune gene repertoire and how the sexes differ in constitutive immune expression.

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.

Variation in intrinsic resistance of pea aphids to parasitoid wasps: A transcriptomic basis

Evolutionary interactions between parasitoid wasps and insect hosts have been well studied at the organismal level, but little is known about the molecular mechanisms that insects use to resist wasp parasitism. Here we study the interaction between a braconid wasp (Aphidius ervi) and its pea aphid host (Acyrthosiphon pisum). We first identify variation in resistance to wasp parasitism that can be attributed to aphid genotype. We then use transcriptome sequencing to identify genes in the aphid genome that are differentially expressed at an early stage of parasitism, and we compare these patterns in highly resistant and susceptible aphid host lines. We find that resistant genotypes are upregulating genes involved in carbohydrate metabolism and several key innate immune system genes in response to parasitism, but that this response seems to be weaker in susceptible aphid genotypes. Together, our results provide a first look into the complex molecular mechanisms that underlie aphid resistance to wasp parasitism and contribute to a broader understanding of how resistance mechanisms evolve in natural populations.

Effects of immune challenge on expression of life-history and immune trait expression in sexually reproducing metazoans-a meta-analysis

BACKGROUND

Life-history theory predicts a trade-off between investment into immune defence and other fitness-related traits. Accordingly, individuals are expected to upregulate their immune response when subjected to immune challenge. However, this is predicted to come at the expense of investment into a range of other traits that are costly to maintain, such as growth, reproduction and survival. Currently, it remains unclear whether the magnitude of such costs, and trade-offs involving immune investment and other traits, manifests consistently across species and sexes. To address this, we conducted a meta-analysis to investigate how changes in sex, ontogenetic stage and environmental factors shape phenotypic trait expression following an immune challenge.

RESULTS

We explored the effects of immune challenge on three types of traits across sexually reproducing metazoans: life-history, morphological and proximate immune traits (235 effect sizes, 53 studies, 37 species [21 invertebrates vs. 16 vertebrates]). We report a general negative effect of immune challenge on survival and reproduction, a positive effect on immune trait expression, but no effect on morphology or development time. The negative effects of immune challenge on reproductive traits and survival were larger in females than males. We also report a pronounced effect of the immune treatment agent used (e.g. whether the treatment involved a live pathogen or not) on the host response to immune challenge, and find an effect of mating status on the host response in invertebrates.

CONCLUSION

These results suggest that costs associated with immune deployment following an immune challenge are context-dependent and differ consistently in their magnitude across the sexes of diverse taxonomic lineages. We synthesise and discuss the outcomes in the context of evolutionary theory on sex differences in life-history and highlight the need for future studies to carefully consider the design of experiments aimed at disentangling the costs of immune deployment.

Macronutrient intake and simulated infection threat independently affect life history traits of male decorated crickets

Nutritional geometry has advanced our understanding of how macronutrients (e.g., proteins and carbohydrates) influence the expression of life history traits and their corresponding trade-offs. For example, recent work has revealed that reproduction and immune function in male decorated crickets are optimized at very different protein:carbohydrate (P:C) dietary ratios. However, it is unclear how an individual's macronutrient intake interacts with its perceived infection status to determine investment in reproduction or other key life history traits. Here, we employed a fully factorial design in which calling effort and immune function were quantified for male crickets fed either diets previously demonstrated to maximize calling effort (P:C = 1:8) or immune function (P:C = 5:1), and then administered a treatment from a spectrum of increasing infection cue intensity using heat-killed bacteria. Both diet and a simulated infection threat independently influenced the survival, immunity, and reproductive effort of males. If they called, males increased calling effort at the low infection cue dose, consistent with the terminal investment hypothesis, but interpretation of responses at the higher threat levels was hampered by the differential mortality of males across infection cue and diet treatments. A high protein, low carbohydrate diet severely reduced the health, survival, and overall fitness of male crickets. There was, however, no evidence of an interaction between diet and infection cue dose on calling effort, suggesting that the threshold for terminal investment was not contingent on diet as investigated here.

Immunometabolic function of the transcription cofactor VGLL3 provides an evolutionary rationale for sexual dimorphism in autoimmunity

Sexual dimorphism is exhibited remarkably in the female predominance of autoimmune diseases (e.g. systemic lupus erythematosus, female-to-male ratio 9 : 1). To understand the female bias in autoimmunity, we focused on vestigial-like family member 3 (VGLL3), a molecule with increased expression in females and known to promote autoimmunity. We report that VGLL3 mediates the cellular stress response by upregulating p53 and IL-17C. Energy stress allows VGLL3 to be induced by IFNα, which ultimately leads to p53-dependent, lupus-associated, inflammatory cell death. Our results suggest that female-biased expression of VGLL3 helps cells adapt to metabolic stress, which, intriguingly, is known as a significant challenge during the evolution of placental mammals due to the need to feed a developing embryo. The findings also uncover the importance of maintaining metabolic homeostasis in the prevention of autoimmunity.

Transcriptome-wide analysis reveals different categories of response to a standardised immune challenge in a wild rodent

Individuals vary in their immune response and, as a result, some are more susceptible to infectious disease than others. Little is known about the nature of this individual variation in natural populations, or which components of immune pathways are most responsible, but defining this underlying landscape of variation is an essential first step to understanding the drivers of this variation and, ultimately, predicting the outcome of infection. We describe transcriptome-wide variation in response to a standardised immune challenge in wild field voles. We find that genes (hereafter 'markers') can be categorised into a limited number of types. For the majority of markers, the response of an individual is dependent on its baseline expression level, with significant enrichment in this category for conventional immune pathways. Another, moderately sized, category contains markers for which the responses of different individuals are also variable but independent of their baseline expression levels. This category lacks any enrichment for conventional immune pathways. We further identify markers which display particularly high individual variability in response, and could be used as markers of immune response in larger studies. Our work shows how a standardised challenge performed on a natural population can reveal the patterns of natural variation in immune response.

Negative associations between parasite avoidance, resistance and tolerance predict host health in salmonid fish populations

Genetic variation in defence against parasite infections is fundamental for host-parasite evolution. The overall level of defence of a host individual or population includes mechanisms that reduce parasite exposure (avoidance), establishment (resistance) or pathogenicity (tolerance). However, how these traits operate and evolve in concert is not well understood. Here, we investigated genetic variation in and associations between avoidance, resistance and tolerance in a natural host-parasite system. Replicated populations of Atlantic salmon (Salmo salar) and sea trout (an anadromous form of brown trout, Salmo trutta) were raised under common garden conditions and infected with the eye fluke Diplostomum pseudospathaceum. We demonstrate significant genetic variation in the defence traits across host populations and negative associations between the traits, with the most resistant populations showing the weakest avoidance and the lowest infection tolerance. These results are suggestive of trade-offs between different components of defence and possibly underlie the genetic variation in defence traits observed in the wild. Because the three defence mechanisms affect host-parasite evolution in profoundly different ways, we emphasize the importance of studying these traits in concert.

Avian Health across the Landscape: Nestling Immunity Covaries with Changing Landcover

The landscape composition of an organism's home range or territory should influence aspects of its condition, including measures of immune function. Changes in immunocompetence arising from variation in landcover may provide important links between habitat changes and patterns of disease spread. To establish a baseline understanding for whether immune measures covary with changes in landcover, we examined associations between immunological parameters and landcover composition for adults and nestlings of five shrubland bird species. Specifically, we examined the bacteria-killing ability (BKA) of the blood plasma and profiles of the five avian leukocytes as our measures of immune function, and assessed the proportion of area around each bird's nest that was composed of the four major landcover types in the Midwestern USA: row crop agriculture, developed, forest, and grass/shrub. We performed landcover assessments at 100 and 1000 m radius buffers to identify whether associations between habitat and immune function differed at the two spatial scales. As part of this work, we examined age and species-related immunological variation, as well as associations among the immune parameters. There was little evidence linking variation in immune function to landcover composition for the adults at either spatial scale, but there were numerous associations for nestlings, and these were stronger at the 1000 than 100 m spatial scale. The proportion of grass/shrub around the nest had the largest impact on immune function, although the effect varied by immune parameter and species. BKA and basophils were inversely associated with grass/shrub for all species, whereas lymphocytes were positively associated with grass/shrub for all species. We also documented species-level differences among adults and nestlings for BKA and all leukocytes except monocytes. As expected, we found that nestlings had reduced levels of BKA, lymphocytes, monocytes, and elevated heterophils compared with adults (except for field sparrow-Spizella pusilla-nestlings, which had higher lymphocytes). Basophils generally did not differ by age class, and eosinophils exhibited species-specific patterns, in which they were higher for nestling American robins (Turdus migratorius) and gray catbirds (Dumetella carolinensis) compared with adults, but lower in the other nestlings. Heterophils and lymphocytes were inversely associated for all species and age classes, and basophil levels were positively associated with BKA across species and age classes. Together, these findings bolster our understanding of age and species-specific variation in immune function, and provide evidence that immune measures can covary with changes in landcover.

Seasonal changes in immune response and reproductive investment in a biparental beetle

Immunity and reproduction are physiologically demanding processes, therefore trade-offs are expected between these life history traits. Furthermore, investments in these traits are also known to be affected by factors such as sex, body size, individual condition, seasonal changes and parasite infection. The relationship between immunity and reproduction and the effect of other factors on this relationship were investigated in many species, but there are a small number of studies on these patterns in biparental invertebrates. Lethrus apterus is an iteroparous biparental beetle with predominant female care in respect of collecting and processing food for larvae. Males guard the nest built underground and also their mate. Here we investigate how sex, body size, time within the reproductive season and parasite load may influence the relationship between immunocompetence and reproductive investment in this species. In beetles from a natural population we quantified immune response by measuring the encapsulation response, antimicrobial activity of hemolymph, the investment into reproductive tissues by measuring the size of testis follicles in males and total egg size in females, and parasite load by counting the number of mites on the beetles. We found that the encapsulation response is condition-dependent, as large individuals showed significantly higher encapsulation ability than small ones. Antimicrobial capacity was significantly higher in females than in males. In case of antimicrobial activity there was also a seasonal change in the relationship between immunity and reproductive investment, but only under heavy mite load. Reproductive investment was influenced by the interaction between body size and season (in females) and by body size and season (in males). Furthermore in females the interaction between antimicrobial activity and season indicated that reproductive investment increased with antimicrobial activity early in the reproductive season. By investigating the relationship between immunity and reproductive investment in a natural population of a biparental beetle species, we can conclude that investments into these important life history traits are governed by complex interactions between physiological and environmental factors. Our results are discussed in the context of life history evolution, highlighting the role of the assessed factors in shaping trade-offs themselves (in invertebrates).

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.

The evolution of resistance and tolerance as cancer defences

Although there is a plethora of cancer associated-factors that can ultimately culminate in death (cachexia, organ impairment, metastases, opportunistic infections, etc.), the focal element of every terminal malignancy is the failure of our natural defences to control unlimited cell proliferation. The reasons why our defences apparently lack efficiency is a complex question, potentially indicating that, under Darwinian terms, solutions other than preventing cancer progression are also important contributors. In analogy with host-parasite systems, we propose to call this latter option ‘tolerance’ to cancer. Here, we argue that the ubiquity of oncogenic processes among metazoans is at least partially attributable to both the limitations of resistance mechanisms and to the evolution of tolerance to cancer. Deciphering the ecological contexts of alternative responses to the cancer burden is not a semantic question, but rather a focal point in understanding the evolutionary ecology of host-tumour relationships, the evolution of our defences, as well as why and when certain cancers are likely to be detrimental for survival.

Antibacterial immune functions of subadults and adults in a semelparous spider

Although capacity to mount an efficient immune response plays a critical role in individuals’ survival, its dynamics across ontogenetic stages is still largely unexplored. Life stage-dependent variation in the encountered diversity and prevalence of parasites were proposed to contribute to stage-dependent changes in immunity, but differences in life history objectives between developmental stages may also lead to stage-specific changes in efficiency of given immune mechanisms. The reason for this is that juveniles and subadults are unable to reproduce, therefore they invest resources mainly into survival, while adults have to partition their resources between survival and reproduction. The general trade-off between somatic maintenance and reproductive effort is expected to impair immune function. Especially so in semelparous organisms that only reproduce once throughout their lifetime, hence they do not face the trade-off between current and future reproduction. We hypothesised that in a semelparous species individuals would be characterised by decreased investment into somatic maintenance after maturation, in order to maximise their reproductive output. Accordingly, we predicted that (1) elements of somatic maintenance, such as immunity, should be relatively weaker in adults in comparison to subadults, and (2) increased reproductive investment in adults should be associated with lower immune efficiency. We quantified two markers of immunity in subadult and adult individuals of the semelparous wolf spider Pardosa agrestis (Westring, 1861), namely bacterial growth inhibition power and bacterial cell wall lytic activity. We found that subadults showed significantly higher cell wall lytic activity than adults, but the two life stages did not differ in their capacity to inhibit bacterial growth. Also, we found weaker immune measures in mated females compared to virgins. Furthermore, in mated females bacterial growth inhibition power was negatively associated with fecundity.