Constitutive Immunity Research Articles

Capacity of blood plasma is higher in birds breeding in radioactively contaminated areas.

BackgroundEnvironmental pollution in general, and radioactive contamination in particular, may deeply affect host-parasite relationships and their consequences for the evolution of organisms. The nuclear accident that occurred more than 30 years ago in Chernobyl resulted in significant changes in diversity and richness of microbial communities that could influence characteristics of animal-bacteria interactions, including host immune responses and competitive interference by bacteria. Given the high mortality rate of birds breeding in radioactively contaminated zones, those with stronger defences against infections should experience significant fitness advantages.Methodology/Principal FindingsHere we characterized antimicrobial capacity of barn swallows (Hirundo rustica) from different Ukrainian populations (subject to a gradient of ionizing radiation) against 12 bacterial species. We also quantified constitutive innate immunity, which is the non-specific first barrier of protection of hosts against microbial parasites. We found a positive association between specific antimicrobial capacity of individual hosts and radiation levels in breeding habitats even after controlling for other confounding variables such as sex and age. However, no significant relationship was found between immunocompetence (non-specific response) and background radiation.Conclusions/SignificanceThese results suggest that radiation selects for broad antimicrobial spectra of barn swallows, although not for all bacterial strains. We discuss these results in the framework of host-parasite evolution under extreme environmental conditions.

Correlates of immune defenses in golden eagle nestlings.

An individual's investment in constitutive immune defenses depends on both intrinsic and extrinsic factors. We examined how Leucocytozoon parasite presence, body condition (scaled mass), heterophil-to-lymphocyte (H:L) ratio, sex, and age affected immune defenses in golden eagle (Aquila chrysaetos) nestlings from three regions: California, Oregon, and Idaho. We quantified hemolytic-complement activity and bacterial killing ability, two measures of constitutive immunity. Body condition and age did not affect immune defenses. However, eagles with lower H:L ratios had lower complement activity, corroborating other findings that animals in better condition sometimes invest less in constitutive immunity. In addition, eagles with Leucocytozoon infections had higher concentrations of circulating complement proteins but not elevated opsonizing proteins for all microbes, and eagles from Oregon had significantly higher constitutive immunity than those from California or Idaho. We posit that Oregon eagles might have elevated immune defenses because they are exposed to more endoparasites than eagles from California or Idaho, and our results confirmed that the OR region has the highest rate of Leucocytozoon infections. Our study examined immune function in a free-living, long-lived raptor species, whereas most avian ecoimmunological research focuses on passerines. Thus, our research informs a broad perspective regarding the evolutionary and environmental pressures on immune function in birds.

Intraspecific differences in molecular stress responses and coral pathobiome contribute to mortality under bacterial challenge in Acropora millepora

Disease causes significant coral mortality worldwide; however, factors responsible for intraspecific variation in disease resistance remain unclear. We exposed fragments of eight Acropora millepora colonies (genotypes) to putatively pathogenic bacteria (Vibrio spp.). Genotypes varied from zero to >90% mortality, with bacterial challenge increasing average mortality rates 4–6 fold and shifting the microbiome in favor of stress-associated taxa. Constitutive immunity and subsequent immune and transcriptomic responses to the challenge were more prominent in high-mortality individuals, whereas low-mortality corals remained largely unaffected and maintained expression signatures of a healthier condition (i.e., did not launch a large stress response). Our results suggest that lesions appeared due to changes in the coral pathobiome (multiple bacterial species associated with disease) and general health deterioration after the biotic disturbance, rather than the direct activity of any specific pathogen. If diseases in nature arise because of weaknesses in holobiont physiology, instead of the virulence of any single etiological agent, environmental stressors compromising coral condition might play a larger role in disease outbreaks than is currently thought. To facilitate the diagnosis of compromised individuals, we developed and independently cross-validated a biomarker assay to predict mortality based on genes whose expression in asymptomatic individuals coincides with mortality rates.

Lag of Immunity Across Seasonal Acclimation States in Gopher Tortoises (Gopherus Polyphemus).

Disease outbreaks are of increasing importance to ectothermic vertebrates as one of numerous results of global change. Anthropogenic climate change is predicted to increase climatic instability, thereby altering natural thermal environments. In this study, we evaluated the direct effects of rapid temperature change on immunity in Gopher Tortoises (Gopherus polyphemus). Specifically, we tested the lag hypothesis, which predicts significant misalignment of optimal and realized immunity when temperature rapidly changes. We assayed constitutive innate immunity, B-cell humoral responses, and heterophil: lymphocyte ratios in response to rapid temperature changes corresponding to realistic changes in body temperature between winter and summer. We found that during summer, rapid temperature reduction caused a series of changes in immunity, including reduced bactericidal ability (P = 0.002), reduced humoral response (P < 0.0001), and increased heterophil:lymphocyte ratios (P < 0.0001). During winter, we found that a temperature increase provided no benefit to immunity. Specifically, there was no increase in bactericidal ability as was predicted by the lag hypothesis. In winter, humoral responses were significantly reduced as a result of rapid warming (P = 0.011) and the rapid warming caused a significant reduction in heterophil:lymphocyte ratios (P < 0.0001). Independent of temperature, we found a significant acclimation effect of winter relative to summer conditions in humoral response (P < 0.001), which showed an overall increase in this parameter during winter. Our findings demonstrate that rapid temperature change, regardless of its direction, is a constraint on immunity in ectothermic vertebrates.

Interaction Between Familial Transmission and a Constitutively Active Immune System Shapes Gut Microbiota in Drosophila melanogaster.

Resident gut bacteria are constantly influencing the immune system, yet the role of the immune system in shaping microbiota composition during an organism’s life span has remained unclear. Experiments in mice have been inconclusive due to differences in husbandry schemes that led to conflicting results. We used Drosophila as a genetically tractable system with a simpler gut bacterial population structure streamlined genetic backgrounds and established cross schemes to address this issue. We found that, depending on their genetic background, young flies had microbiota of different diversities that converged with age to the same Acetobacteraceae-dominated pattern in healthy flies. This pattern was accelerated in immune-compromised flies with higher bacterial load and gut cell death. Nevertheless, immune-compromised flies resembled their genetic background, indicating that familial transmission was the main force regulating gut microbiota. In contrast, flies with a constitutively active immune system had microbiota readily distinguishable from their genetic background with the introduction and establishment of previously undetectable bacterial families. This indicated the influence of immunity over familial transmission. Moreover, hyperactive immunity and increased enterocyte death resulted in the highest bacterial load observed starting from early adulthood. Cohousing experiments showed that the microenvironment also played an important role in the structure of the microbiota where flies with constitutive immunity defined the gut microbiota of their cohabitants. Our data show that, in Drosophila, constitutively active immunity shapes the structure and density of gut microbiota.

Life-history dependent relationships between body condition and immunity, between immunity indices in male Eurasian tree sparrows

In free-living animals, recent evidence indicates that innate, and acquired, immunity varies with annual variation in the demand for, and availability of, food resources. However, little is known about how animals adjust the relationships between immunity and body condition, and between innate and acquired immunity to optimize survival over winter and reproductive success during the breeding stage. Here, we measured indices of body condition (size-corrected mass [SCM], and hematocrit [Hct]), constitutive innate immunity (plasma total complement hemolysis activity [CH50]) and acquired immunity (plasma immunoglobulin A [IgA]), plus heterophil/lymphocyte (H/L) ratios, in male Eurasian tree sparrows (Passer montanus) during the wintering and the breeding stages. We found that birds during the wintering stage had higher IgA levels than those from the breeding stage. Two indices of body condition were both negatively correlated with plasma CH50 activities, and positively with IgA levels in wintering birds, but this was not the case in the breeding birds. However, there was no correlation between CH50 activities and IgA levels in both stages. These results suggest that the relationships between body condition and immunity can vary across life-history stage, and there are no correlations between innate and acquired immunity independent of life-history stage, in male Eurasian tree sparrows. Therefore, body condition indices predict immunological state, especially during the non-breeding stage, which can be useful indicators of individual immunocompetences for understanding the variations in innate and acquired immunity in free-living animals.

Inducible versus constitutive social immunity: examining effects of colony infection on glucose oxidase and defensin-1 production in honeybees.

Honeybees use a variety of defence mechanisms to reduce disease infection and spread throughout the colony. Many of these defences rely on the collective action of multiple individuals to prevent, reduce or eradicate pathogens—often referred to as ‘social immunity’. Glucose oxidase (GOX) and some antimicrobial peptides (e.g. defensin-1 or Def1) are secreted by the hypopharyngeal gland of adult bees on larval food for their antiseptic properties. Because workers secrete these compounds to protect larvae, they have been used as ‘biomarkers’ for social immunity. The aim of this study was to investigate if GOX and Def1 are induced after pathogen exposure to determine whether its production by workers is the result of a collective effort to protect the brood and colony in response to a pathogen challenge. Specifically, we quantified GOX and Def1 in honeybee adults before and after colony-level bacterial infection by American foulbrood ((AFB), Paenibacillus larvae). Overall, our results indicate that levels of GOX and Def1 are not induced in response to pathogenic infections. We therefore conclude that GOX and Def1 are highly constitutive and co-opted as mechanisms of social immunity, and these factors should be considered when investigating immunity at the individual and colony level in social insects.

Circulating Antimicrobial Peptide LL-37 Status in Type 1 Diabetes Mellitus and its Relation with Glycemic Control

Antimicrobial-peptides are important molecules of constitutive innate immunity. Though patients with diabetes mellitus are generally prone to infections, there is limited information on their antimicrobialpeptide status. We assessed the circulating LL-37 antimicrobial peptide (also referred as cathelicidin) levels in patients with type 1 diabetes mellitus and its relation with their glycemic status. The LL-37 mRNA expression was assessed in the peripheral blood mononuclear cells (PBMC) by quantitative RT-PCR usingβ-actin and cytochrome-C1 as the reference genes in 154 subjects (Type 1 diabetes, n=111 and healthy subjects, n=43). Serum LL-37 was quantified using sandwich-ELISA. Average HbA1c over last 2 years and current HbA1c were used to determine long-term and short-term glycemic status. LL-37 mRNA expression and serum LL-37 levels were correlated with the glycemic status. The LL-37 mRNA copies were comparable between type 1 diabetes and healthy subjects [median (IQR) = 6.7 (1.8–15.28) vs. 7.2 (2.23–21.86), respectively, P = 0.42]. There was no significant difference in serum LL-37 levels between the two groups [median (IQR) = 3.9 (2.88–7.52) vs. 5.0 (3.19–9.05) ng/ml, respectively, P = 0.52]. The LL-37 mRNA and its protein concentration showed no significant correlation with the average or current HbA1c values. The constitutive circulating antimicrobial peptide LL-37 status is not significantly altered in patients with type 1 diabetes mellitus and also not affected by their glycemic status.

Cheetahs have a stronger constitutive innate immunity than leopards

As a textbook case for the importance of genetics in conservation, absence of genetic variability at the major histocompatibility complex (MHC) is thought to endanger species viability, since it is considered crucial for pathogen resistance. An alternative view of the immune system inspired by life history theory posits that a strong response should evolve in other components of the immune system if there is little variation in the MHC. In contrast to the leopard (Panthera pardus), the cheetah (Acinonyx jubatus) has a relatively low genetic variability at the MHC, yet free-ranging cheetahs are healthy. By comparing the functional competence of the humoral immune system of both species in sympatric populations in Namibia, we demonstrate that cheetahs have a higher constitutive innate but lower induced innate and adaptive immunity than leopards. We conclude (1) immunocompetence of cheetahs is higher than previously thought; (2) studying both innate and adaptive components of immune systems will enrich conservation science.

Immune function trade-offs in response to parasite threats

Immune function is often involved in physiological trade-offs because of the energetic costs of maintaining constitutive immunity and mounting responses to infection. However, immune function is a collection of discrete immunity factors and animals should allocate towards factors that combat the parasite threat with the highest fitness cost. For example, animals on dispersal fronts of expanding population may be released from density-dependent diseases. The costs of immunity, however, and life history trade-offs in general, are often context dependent. Trade-offs are often most apparent under conditions of unusually limited resources or when animals are particularly stressed, because the stress response can shift priorities. In this study we tested how humoral and cellular immune factors vary between phenotypes of a wing dimorphic cricket and how physiological stress influences these immune factors. We measured constitutive lysozyme activity, a humoral immune factor, and encapsulation response, a cellular immune factor. We also stressed the crickets with a sham predator in a full factorial design. We found that immune strategy could be explained by the selective pressures encountered by each morph and that stress decreased encapsulation, but not lysozyme activity. These results suggest a possible trade-off between humoral and cellular immunity. Given limited resources and the expense of immune factors, parasite pressures could play a key factor in maintaining insect polyphenism via disruptive selection.

Inducible versus constitutive social immunity: examining effects of colony infection on glucose oxidase and defensin-1 production in honeybees

Inducible versus constitutive social immunity: examining effects of colony infection on glucose oxidase and defensin-1 production in honeybees

Sources of variance in immunological traits: evidence of congruent latitudinal trends across species.

Among-population differences in immunological traits allow assessment of both evolutionary and plastic changes in organisms' resistance to pathogens. Such knowledge also provides information necessary to predict responses of such traits to environmental changes. Studies on latitudinal trends in insect immunity have so far yielded contradictory results, suggesting that multispecies approaches with highly standardised experimental conditions are needed. Here, we studied among-population differences of two parameters reflecting constitutive immunity-phenoloxidase (PO) and lytic activity, using common-garden design on three distantly related moth species represented by populations ranging from northern Finland to Georgia (Caucasus). The larvae were reared at different temperatures and on different host plants under a crossed factors experimental design. Haemolymph samples for measurement of immune status were taken from the larvae strictly synchronously. Clear among-population differences could be shown only for PO activity in one species (elevated activity in the northern populations). There was some indication that the cases of total absence of lytic activity were more common in southern populations. The effects of temperature, host and sex on the immunological traits studied remained highly species specific. Some evidence was found that lytic activity may be involved in mediating trade-offs between immunity and larval growth performance. In contrast, PO activity rarely covaried with fitness-related traits, and neither were the values of PO and lytic activity correlated with each other. The relatively inconsistent nature of the detected patterns suggests that studies on geographic differences in immunological traits should involve multiple species, and rely on several immunological indices if general trends are a point of interest.

Diet effects on bumblebee health

Among physiological processes, the maintenance of immunity is one of the most energetically costly in invertebrates. Disease resistance can be quantified by measuring immunocompetence, which is defined as the ability of an organism to mount an immune response, either in cellular, humoral or behavioural forms. In insects, immune capacity can be affected by a variety of factors including pesticides, genetic diversity or diet. Here we focus on an important species of domesticated pollinator, Bombus terrestris, and the potential impact of a poor pollen diet (low nutritional content and toxic) on its health. We investigate three responses at both colony and individual levels: behavioural, humoral and cellular. Our results show that poor pollen diets decrease larval and pupal masses and increase larval ejection as well as adult constitutive immunity (i.e., prophenoloxidase assays). The susceptibility of bumblebees to disease and infection might therefore be greater after a nutritive stress. These findings raise the importance of available plant hosts, especially floral plant species providing pollen with suitable nutritive quality (i.e., nutrient pollen content) for bumblebees.

Negative impact of urban habitat on immunity in the great tit Parus major.

Urban habitats are described as having an overall negative influence on many fitness-related traits in several bird species, but a vital function such as immunity remains poorly studied. The immune response is strongly linked to individual condition, which partly depends on resource availability and the parasitic context that often differ between urban and natural habitats. A difference between the immunity of populations dwelling in urban areas and populations from more natural habitats can, therefore, be hypothesized. We conducted a 2-year experimental study on great tits (Parus major) in urban and forest areas. We stimulated the constitutive immunity of nestlings and assessed both the inflammatory response by measuring the plasma levels of haptoglobin, an inflammatory marker, and its activation cost through the loss of body mass. In addition, we checked the nestlings for ectoparasites and assessed haemosporidian prevalence in adults. Nestlings from urban sites produced relatively less haptoglobin and lost more body mass than those from forest sites, which suggests that the activation of constitutive immunity is more costly for birds living in urban sites than for those living in the forest. We detected no ectoparasite in birds in both habitats. However, urban adults showed lower haemosporidian prevalence than forest ones, suggesting a reduced exposure to these parasites and their vectors in towns. Overall, our study provides evidence for an immune difference between urban and forest populations. Because immunity is crucial for organism fitness, it is of prime interest to identify causes and processes at the origin of this difference.

Seasonal Acclimation of Constitutive Immunity in Gopher Tortoises Gopherus polyphemus.

Studies have suggested a role for natural seasonal change to drive patterns of disease, especially within ectothermic vertebrates. In light of recent climate change, it is important to understand baseline disease resistance in a seasonal context to further understand the role that changes in seasonal weather patterns may have in increasing disease frequency. Herein we found support for the seasonal acclimation hypothesis in Gopherus polyphemus (gopher tortoise), which indicated that natural seasonal variation causes differences in baseline immune function across seasonal acclimation states. We found that an innate immune parameter, bactericidal ability (BA), was significantly elevated in the summer (P < 0.00001). Circulating leukocyte profiles varied significantly among seasons, with heterophils and monocytes increased (P = 0.00019 and P = 0.0001, respectively) and lymphocytes decreased (P < 0.00001) during winter. We assayed baseline glucocorticoid concentration (e.g., corticosterone [CORT]) across seasons and sampling conditions to test whether CORT drove the seasonal pattern in immunological acclimation. CORT was significantly lowest during winter and in animals temporarily maintained in seminatural conditions. These changes in CORT occurred independently of the immunological adjustments, suggesting that the seasonal pattern of immunity was not mediated by CORT secretion. The reduction in lymphocytes and BA and also BA during winter suggest that seasonal acclimation is likely a restraint on energetic output when temperature is low and physiological performance is thermally constrained. While these parameters were reduced in winter, the increase in heterophils and monocytes may indicate a compensatory immune adjustment to increase the number of innate phagocytic cells.

Diet Drives the Collective Migrations and Affects the Immunity of Mormon Crickets and Locusts: A Comparison of These Potential Superspreaders of Disease.

Differential transmission of disease among individuals within a population or among species in a community can result in superspreaders, relatively rare individuals responsible for a large proportion of transmission events. Migrating Mormon crickets and nymphal locusts readily engage in cannibalistic attacks and necrophagy. Typically multiple individuals consume a cadaver, which fosters the spread of disease. Cannibalistic attacks result in aligned, coordinated movement of individuals in massive bands that march daily for weeks at a time. Coordinated movement reduces contact frequency, which not only reduces cannibalism but the risk of disease transmission. When crowded, Mormon crickets and locusts elevate their constitutive immunity, which further reduces the risk of disease transmission. Bands of Mormon crickets show a variety of macronutrient dietary deficiencies that determine whether they will be more susceptible to pathogenic bacteria or fungi. In some migratory bands, Mormon crickets seek carbohydrates and have less anti-bacterial activity. A lipid transport protein that functions in both fuelling migration and anti-bacterial activity may cause a trade-off between the two activities when carbohydrates are limited. In other migratory bands, Mormon crickets prefer protein over carbohydrates, indicating protein-deficiency. In these bands, the generalized immunity of Mormon crickets, measured as phenoloxidase, is compromised, and the insects are more susceptible to Beauveria bassiana fungal infection. In locusts, a high protein diet resulted in greater susceptibility to another entomopathogenic fungus, Metarhizium acridum, whereas in Mormon crickets, both phenoloxidase titers and immunity to M acridum increased with adult age. Color changes associated with death by either of these fungi diminishes cannibalism, but bands may cull infected or encounter cadavers too quickly to effectively reduce fungal transmission. As long as the insects show no signs of infection that ward off their conspecifics, then infected Mormon crickets and locusts in migratory bands could be superspreaders of disease. However, the diseases that they are most likely to harbor and amplify may depend on the dietary deficiencies exhibited by members of the band.

Coevolutionary feedback elevates constitutive immune defence: a protein network model.

BackgroundOrganisms have evolved a variety of defence mechanisms against natural enemies, which are typically used at the expense of other life history components. Induced defence mechanisms impose minor costs when pathogens are absent, but mounting an induced response can be time-consuming. Therefore, to ensure timely protection, organisms may partly rely on constitutive defence despite its sustained cost that renders it less economical. Existing theoretical models addressing the optimal combination of constitutive versus induced defence focus solely on host adaptation and ignore the fact that the efficacy of protection depends on genotype-specific host-parasite interactions. Here, we develop a signal-transduction network model inspired by the invertebrate innate immune system, in order to address the effect of parasite coevolution on the optimal combination of constitutive and induced defence.ResultsOur analysis reveals that coevolution of parasites with specific immune components shifts the host’s optimal allocation from induced towards constitutive immunity. This effect is dependent upon whether receptors (for detection) or effectors (for elimination) are subjected to parasite counter-evolution. A parasite population subjected to a specific immune receptor can evolve heightened genetic diversity, which makes parasite detection more difficult for the hosts. We show that this coevolutionary feedback renders the induced immune response less efficient, forcing the hosts to invest more heavily in constitutive immunity. Parasites diversify to escape elimination by a specific effector too. However, this diversification does not alter the optimal balance between constitutive and induced defence: the reliance on constitutive defence is promoted by the receptor’s inability to detect, but not the effectors’ inability to eliminate parasites. If effectors are useless, hosts simply adapt to tolerate, rather than to invest in any defence against parasites. These contrasting results indicate that evolutionary feedback between host and parasite populations is a key factor shaping the selection regime for immune networks facing antagonistic coevolution.ConclusionParasite coevolution against specific immune defence alters the prediction of the optimal use of defence, and the effect of parasite coevolution varies between different immune components.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0667-3) contains supplementary material, which is available to authorized users.

Lead exposure reduces carotenoid-based coloration and constitutive immunity in wild mallards.

The ingestion of spent lead (Pb) from ammunition is a known cause of mortality in waterfowl, but little is known about sublethal effects produced by Pb poisoning on birds, especially in wild populations. The authors studied potential sublethal effects associated with Pb exposure in mallards (Anas platyrhynchos) from the Ebro delta (northeastern Spain) after a ban on Pb ammunition. They analyzed the relationships between blood Pb levels and oxidative stress, immune response, and carotenoid-based coloration, which are known to be influenced by oxidative stress. Levels of Pb were reduced by half from 6 yr to 9 yr after the ban. Lipid peroxidation was positively related to Pb levels in females. The δ-aminolevulinic acid dehydratase activity was suppressed by Pb exposure and negatively associated with the activity of antioxidant enzymes. Carotenoid levels were positively associated with blood Pb concentration in both sexes, and males with higher Pb levels presented a less intense coloration in legs and beak. Levels of Pb were positively related to hemolytic activity of circulating immune system components and negatively related to lysozyme levels. In summary, Pb exposure was associated in a gender-specific way with increased oxidative stress, consequences on color expression, and impaired constitutive immunity. In females, antioxidants seemed to be allocated mostly in reproduction rather than in self-maintenance, whereas males seemed to better maintain oxidative balance to the detriment of coloration. Environ Toxicol Chem 2016;35:1516-1525. © 2015 SETAC.

Baculovirus-challenge and poor nutrition inflict within-generation fitness costs without triggering transgenerational immune priming

Invertebrate hosts that survive pathogen challenge can produce offspring that are more resistant to the same pathogen via immune priming, thereby improving the fitness of their offspring in the same pathogen environment. Most evidence for immune priming comes from exposure to bacteria and there are limited data on other groups of pathogens. Poor parental nutrition has also been shown to result in the transgenerational transfer of pathogen resistance and increased immunocompetence. Here, we combine exposure to an insect DNA virus with a change in the parental diet to examine both parental costs and transgenerational immune priming. We challenged the cabbage looper, Trichoplusia ni, with a low dose of the baculovirus, Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and altered dietary protein to carbohydrate ratio (p:c ratio) after virus exposure. Insects fed a low protein diet had lower haemolymph protein concentrations, and exhibited costs of smaller pupae and slower development, while survivors of virus challenge developed more slowly, irrespective of p:c ratio, and those that were virus-challenged and fed on a low protein diet showed a reduction in haemocyte density. In addition, AcMNPV-challenged parents laid fewer eggs earlier in egg laying although egg size was the same as for unchallenged parents. There was no evidence for increased resistance to AcMNPV (immune priming) or changes in haemocyte number (as proxy for constitutive cellular immunity) in the offspring either as a result of parental AcMNPV-challenge or low dietary p:c ratio. Therefore, although pathogen-challenge and nutritional changes can affect host development and reproduction, this does not necessarily translate into transgenerational immune priming. Our findings contrast with an earlier study on another type of baculovirus, a granulovirus, where immune priming was suggested. This indicates that transgenerational immune priming is not universal in invertebrates and is likely to depend on the host-pathogen system, or the level of pathogen exposure and the type of dietary manipulation. Identifying whether immune priming or transgenerational effects are relevant in field populations, remains a challenge.

Vitally important - does early innate immunity predict recruitment and adult innate immunity?

The immune system is one of the most important adaptations that has evolved to protect animals from a wide range of pathogens they encounter from early life onwards. During the early developmental period this is particularly true for the innate immunity, as other components of the immune system are, as yet, poorly developed. But innate immunity may not only be crucial for early life survival, but may also have long‐lasting effects, for example if early life immunity reflects the functioning of the immune system as a whole. For this reason, we investigated the importance of four constitutive innate immune parameters (natural antibodies, complement activity, concentrations of haptoglobin, and concentrations of nitric oxide) for recruitment in free‐living great tits. We compared nestling immunity of recruits with nestling immunity of their nonrecruited siblings. We also investigated within individual consistency of these innate immune parameters for those individuals that recruited, which may be taken as a measure of immune capacity. In accordance with previous studies, we found a clear effect of tarsus length and a trend for body mass on the likelihood to recruit. Nevertheless, we found no evidence that higher levels of constitutive innate immunity as a nestling facilitated local recruitment. Furthermore, individual innate immunity was not consistent across life stages, that is to say, nestling immune parameters did not determine, or respectively, reflect adult innate immune parameters. This plasticity in innate immune components may explain why we did not find long‐lasting survival benefits.