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The general development of immune response in the short and long term is a product of the antigenic environment in which a species resides. Colonization of a novel antigenic environment by a species would be expected to alter the immune system. Animals that successfully adapt their immune responses will successfully colonize new locations. However, founder events associated with colonization by limited numbers of individuals from a source population will constrain adaptability. How these contradicting forces shape immunity in widely distributed species is unknown. The western house mouse (Mus musculus domesticus) spread globally from the Indo-Pakistani cradle, often in association with human migration and settlement. In the present study, we tested the hypothesis that wild-derived outbred laboratory populations of house mice from their original range (Iran) and historically recent European invasive populations (from France and Germany) present differences in immune functional diversity corresponding to recent historical founder events in Europe and movement to novel antigenic environments. We found that (1) European mice had lower total white blood cell (WBC) counts but higher immunoglobulin E concentrations than their Iranian counterparts, and (2) there were no significant differences in the measured immunological parameters among European populations. The results indicate that founder events in European mice and selection pressure exerted by the composition of local parasitic helminth communities underlie the observed patterns.

The gut microbiota-immune-brain axis is a feedback network which influences diverse physiological processes and plays a pivotal role in overall health and wellbeing. Although research in humans and laboratory mice has shed light into the associations and mechanisms governing this communication network, evidence of such interactions in wild, especially in young animals, is lacking. We therefore investigated these interactions during early development in a population of common buzzards (Buteo buteo) and their effects on individual condition. In a longitudinal study, we used a multi-marker approach to establish potential links between the bacterial and eukaryotic gut microbiota, a panel of immune assays and feather corticosterone measurements as a proxy for long-term stress. Using Bayesian structural equation modeling, we found no support for feedback between gut microbial diversity and immune or stress parameters. However, we did find strong relationships in the feedback network. Immunity was negatively correlated with corticosterone levels, and microbial diversity was positively associated with nestling body condition. Furthermore, corticosterone levels and eukaryotic microbiota diversity decreased with age while immune activity increased. The absence of conclusive support for the microbiota-immune-brain axis in common buzzard nestlings, coupled with the evidence for stressmediated immunosuppression, suggests a dominating role of stress-dominated maturation of the immune system during early development. Confounding factors inherent to wild systems and developing animals might override associations known from adult laboratory model subjects. The positive association between microbial diversity and body condition indicates the potential health benefits of possessing a diverse and stable microbiota. [ABSTRACT FROM AUTHOR]

Many songbirds migrate twice a year to exploit seasonally available resources. These journeys are energetically demanding and energy reserves of these small birds are limited. Accordingly, most of the time migrating is spent during stopovers that serve to rest, replenish resources and recover. While external influences, like prevailing weather conditions and resource availability, are well studied with regard to stopover behaviour and departure decisions, studies on how birds' individual physiological condition and stopover decisions may be linked are scarce.We used a large‐scale radio‐telemetry network covering the German Bight (SE North Sea) to study how birds' immunological constitution at stopover may correlate with departure and flight behaviour in five species of short‐ to medium‐distance migratory songbirds. We measured markers of the innate (bacterial killing activity, lysozyme concentration, natural antibodies and complement titres) and acquired immune function (immunoglobulin Y) in the birds' plasma. After sampling, we tracked the birds' behaviour in terms of stopover duration as well as flight routes and flight distances within the telemetry network after departure.We found that stopover durations were positively related to natural antibodies and immunoglobulin Y across species and to the bacterial killing activity solely in song thrushes in spring, while no relations became apparent in fall. Flight distances were linked positively to immunoglobulin Y concentrations in both spring and fall, though not in all of the investigated species. Coastal and offshore‐oriented routes were taken independent of the birds' immune status.Our study for the first time shows that migratory behaviour of songbirds in the wild is correlated with their immune status, not only during but also beyond stopover. Furthermore, birds with increased complement titres and Immunoglobulin Y concentrations, either due to recent infection or greater investment in their immune function, took additional time at their stopover sites, probably to reach their breeding grounds in good condition. During the less time‐constrained fall season, stopovers were generally prolonged, independent from the birds' immune status and any delays taken to improve immune status are most likely not detrimental in terms of fitness. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Sex‐specific physiology is commonly reported in animals, often indicating lower immune indices and higher oxidative stress in males than in females. Sexual selection is argued to explain these differences, but empirical evidence is limited. Here, we explore sex differences in immunity, oxidative physiology and packed cell volume of wild, adult, breeding birds (97 species, 1997 individuals, 14 230 physiological measurements). We show that higher female immune indices are most common across birds (when bias is present), but oxidative physiology shows no general sex‐bias and packed cell volume is generally male‐biased. In contrast with predictions based on sexual selection, male‐biased sexual size dimorphism is associated with male‐biased immune measures. Sexual dichromatism, mating system and parental roles had no effect on sex‐specificity in physiology. Importantly, female‐biased immunity remained after accounting for sexual selection indices. We conclude that cross‐species differences in physiological sex‐bias are largely unrelated to sexual selection and alternative explanations should be explored. [ABSTRACT FROM AUTHOR]

Reproduction is one of the costliest processes in the life of an animal. Life history theory assumes that when resources are limiting allocation to reproduction will reduce allocation to other essential processes thereby inducing costs of reproduction. The immune system is vital for survival. If reproduction reduces investment in immune function, this could increase the risk of disease, morbidity and mortality. We here test in the guinea pig, if even under ad libitum food conditions, pregnancy and lactation reduce the activity of the adaptive and innate immune system compared to the reaction of non-reproducing animals. In response to a challenge with keyhole limpet haemocyanin the antibody-mediated adaptive immunity during (pregnancy and) lactation was reduced. Pregnant and lactating females showed higher levels of bacterial killing activity, an integrated measure of innate immunity, than non-reproducing females. However, two major effectors of the innate immunity, the natural antibody and the complement of pregnant and lactating females showed lower levels than in non-reproducing females. Pregnant and lactating females did not differ significantly in the expressed levels of innate immunity. Our results indicate that changes in the immune response during reproduction are physiological adjustments to predictable allocation problems, because they happen even under ad libitum food availability. [ABSTRACT FROM AUTHOR]

The immune system imposes costs that may have to be traded against investment of resources in other costly life-history traits. Yet, it is unknown if a trade-off between immunity and longevity occurs in free-ranging mammals. Here, we tested if age and survival, two aspects associated with longevity, are linked to immune parameters in an 8 g bat species. Using a combination of cross-sectional and longitudinal data, we assessed whether total white blood cell (WBC) counts, bacterial killing ability of the plasma (BKA) and immunoglobulin G (IgG) concentration change with age. Furthermore, we asked if these immune parameters impose costs resulting in decreased survival probabilities. We found that WBC counts decreased with age both within and among individuals. IgG concentrations were higher in older individuals, but did not change with age within individuals. Furthermore, individuals with above average WBC counts or IgG concentration had lower probabilities to survive the next six months. High WBC counts and IgG concentrations may reflect infections with parasites and pathogens, however, individuals that were infected with trypanosomes or nematodes showed neither higher WBC counts or IgG concentrations, nor was infection connected with survival rates. BKA was higher in infected compared with uninfected bats, but not related to age or survival. In conclusion, cellular (WBC) and humoral (IgG) parts of the immune system were both connected to age and survival, but not to parasite infections, which supports the hypothesis that energetically costly immunological defences are traded against other costly life-history traits, leading to a reduced lifespan in this free-ranging mammal. [ABSTRACT FROM AUTHOR]

Maintaining a competent immune system is energetically costly and thus immunity may be traded against other costly traits such as seasonal migration. Here, we tested in long-distance migratory Nathusius' pipistrelles (Pipistrellus nathusii), if selected branches of immunity are expressed differently in response to the energy demands and oxidative stress of aerial migration. During the migration period, we observed higher baseline lymphocyte and lower neutrophil levels than during the pre-migration period, but no stronger response of cellular effectors to an antigen challenge. Baseline plasma haptoglobin, as a component of the humoral innate immunity, remained similar during both seasons, yet baseline plasma haptoglobin levels increased by a factor of 7.8 in migratory bats during an immune challenge, whereas they did not change during the pre-migration period. Oxidative stress was higher during migration than during pre-migration, yet there was no association between blood oxidative status and immune parameters, and immune challenge did not trigger any changes in oxidative stress, irrespective of season. Our findings suggest that humoral effectors of the acute phase response may play a stronger role in the first-line defense against infections for migrating bats compared to non-migrating bats. We conclude that Nathusius' pipistrelles allocate resources differently into the branches of their immune system, most likely following current demands resulting from tight energy budgets during migration. [ABSTRACT FROM AUTHOR]