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.

Physiological responses of host parents to rearing an avian brood parasite: An experimental study.

Raising an obligate avian brood parasite is costly for host parents because it redirects valuable parental resources from one's own offspring to genetically unrelated young. The costs of raising a brood parasite may be mediated by physiological stressors for foster parents if it requires greater or biased parental effort compared to raising non-parasitized broods. For example, upregulating glucocorticoid hormones or reducing immune responses may mediate a trade-off between resource allocation to a current brood versus future reproductive opportunities, but published data on parasitized hosts' physiology are scarce. Here we used an experimental approach to test if host parents respond to the presence of brood parasitic young through dynamic changes in their own physiology. We conducted our experiments with parasitic brown-headed cowbirds (Molothrus ater) fostered into nests of host prothonotary warblers (Protonotaria citrea). Relative to parents caring for non-parasitized control broods, parasitism increased baseline corticosterone levels and reduced body mass in adult male, but not in female, hosts. Immune responses to a novel antigen were depressed in both parents of parasitized broods compared to parents of non-parasitized broods. Additionally, we found that immune function increased along the breeding season regardless of treatment. These experiments also confirmed prior observational data that parasitized adult males have reduced return rates to breeding sites in years subsequent to raising cowbirds. The findings demonstrate diverse physiological effects of parasitism on the foster parents in our particular host-brood parasite system, yet we found no evidence of individual trade-offs between endocrine and immune responses of adult hosts.

Antiviral Activity and Adaptive Evolution of Avian Tetherins.

Tetherin/BST-2 is an antiviral protein that blocks the release of enveloped viral particles by linking them to the membrane of producing cells. At first, BST-2 genes were described only in humans and other mammals. Recent work identified BST-2 orthologs in nonmammalian vertebrates, including birds. Here, we identify the BST-2 sequence in domestic chicken (Gallus gallus) for the first time and demonstrate its activity against avian sarcoma and leukosis virus (ASLV). We generated a BST-2 knockout in chicken cells and showed that BST-2 is a major determinant of an interferon-induced block of ASLV release. Ectopic expression of chicken BST-2 blocks the release of ASLV in chicken cells and of human immunodeficiency virus type 1 (HIV-1) in human cells. Using metabolic labeling and pulse-chase analysis of HIV-1 Gag proteins, we verified that chicken BST-2 blocks the virus at the release stage. Furthermore, we describe BST-2 orthologs in multiple avian species from 12 avian orders. Previously, some of these species were reported to lack BST-2, highlighting the difficulty of identifying sequences of this extremely variable gene. We analyzed BST-2 genes in the avian orders Galliformes and Passeriformes and showed that they evolve under positive selection. This indicates that avian BST-2 is involved in host-virus evolutionary arms races and suggests that BST-2 antagonists exist in some avian viruses. In summary, we show that chicken BST-2 has the potential to act as a restriction factor against ASLV. Characterizing the interaction of avian BST-2 with avian viruses is important in understanding innate antiviral defenses in birds.IMPORTANCE Birds are important hosts of viruses that have the potential to cause zoonotic infections in humans. However, only a few antiviral genes (called viral restriction factors) have been described in birds, mostly because birds lack counterparts of highly studied mammalian restriction factors. Tetherin/BST-2 is a restriction factor, originally described in humans, that blocks the release of newly formed virus particles from infected cells. Recent work identified BST-2 in nonmammalian vertebrate species, including birds. Here, we report the BST-2 sequence in domestic chicken and describe its antiviral activity against a prototypical avian retrovirus, avian sarcoma and leukosis virus (ASLV). We also identify BST-2 genes in multiple avian species and show that they evolve rapidly in birds, which is an important indication of their relevance for antiviral defense. Analysis of avian BST-2 genes will shed light on defense mechanisms against avian viral pathogens.

Geographic variation in baseline innate immune function does not follow variation in aridity along a tropical environmental gradient.

Geographic variation in aridity determines environmental productivity patterns, including large-scale variability in pathogens, vectors and associated diseases. If disease risk decreases with increasing aridity and is matched by immune defense, we predict a decrease in innate immune function along a gradient of increasing aridity from the cool-wet forest to the hot-dry Sahel, from south to north in Nigeria. We sampled blood and measured five innate immune indices from 286 Common Bulbuls Pycnonotus barbatus between 6 and 13°N. We sampled in the dry season; we resampled the first location (Jos) also as the last sample location to test temporal change in immune function. Immune indices did not decrease with aridity. One immune index, nitric oxide concentration showed a weak quadratic pattern. In Jos, ovotransferrin concentration, haemagglutination and haemolysis titres increased 12 weeks into the dry season, contrary to expectations that immune indices should decrease with increased dryness. In this tropical system, innate immune function does not decrease with increasing aridity but temporal factors within a location may influence immune function more strongly than spatial variation in aridity, suggesting that immune variation does not follow a simple environmental productivity pattern. Consequently, caution should probably be exercised in predicting effects of climate variability on immune function or disease risk.

Association between louse abundance and MHC II supertypes in Galápagos mockingbirds.

Major histocompatibility complex class II (MHC II) is an essential molecule triggering the adaptive immune response by the presentation of pathogens to helper T cells. The association between individual MHC II variants and various parasites has become a frequent finding in studies of vertebrate populations. However, although bird ectoparasites have a significant effect on their host's fitness, and the host's immune system can regulate ectoparasitic infections, no study has yet investigated the association between MHC II polymorphism and ectoparasite infection in the populations of free-living birds. Here, we test whether an association exists between the abundance of a chewing louse (Myrsidea nesomimi) and MHC II polymorphism of its hosts, the Galápagos mockingbirds (Mimus). We have found that the presence of two MHC II supertypes (functionally differentiated clusters) was significantly associated with louse abundance. This pattern supports the theory that a co-evolutionary interaction stands behind the maintenance of MHC polymorphism. Moreover, we have found a positive correlation between louse abundance and heterophil/lymphocyte ratio (an indicator of immunological stress) that serves as an additional piece of evidence that ectoparasite burden is affected by immunological state of Galápagos mockingbirds.

Immunogenetic response of the bananaquit in the face of malarial parasites.

BACKGROUND: In the arms race between hosts and parasites, genes involved in the immune response are targets for natural selection. Toll-Like Receptor (TLR) genes play a role in parasite detection as part of the innate immune system whereas Major Histocompatibility Complex (MHC) genes encode proteins that display antigens as part of the vertebrate adaptive immune system. Thus, both gene families are under selection pressure from pathogens. The bananaquit (Coereba flaveola) is a passerine bird that is a common host of avian malarial parasites (Plasmodium sp. and Haemoproteus sp.). We assessed molecular variation of TLR and MHC genes in a wild population of bananaquits and identified allelic associations with resistance/susceptibility to parasitic infection to address hypotheses of avian immune response to haemosporidian parasites. RESULTS: We found that allele frequencies are associated with infection status at the immune loci studied. A consistent general trend showed the infected groups possessed more alleles at lower frequencies, and exhibited unique alleles, compared to the uninfected group. CONCLUSIONS: Our results support the theory of natural selection favoring particular alleles for resistance while maintaining overall genetic diversity in the population, a mechanism which has been demonstrated in some systems in MHC previously but understudied in TLRs.

Mitigating the impact of microbial pressure on great (Parus major) and blue (Cyanistes caeruleus) tit hatching success through maternal immune investment.

The hatching success of a bird's egg is one of the key determinants of avian reproductive success, which may be compromised by microbial infections causing embryonic death. During incubation, outer eggshell bacterial communities pose a constant threat of pathogen translocation and embryo infection. One of the parental strategies to mitigate this threat is the incorporation of maternal immune factors into the egg albumen and yolk. It has been suggested that habitat changes like forest fragmentation can affect environmental factors and life-history traits that are linked to egg contamination. This study aims at investigating relationships between microbial pressure, immune investment and hatching success in two abundant forest bird species and analyzing to what extent these are driven by extrinsic (environmental) factors. We here compared (1) the bacterial load and composition on eggshells, (2) the level of immune defenses in eggs, and (3) the reproductive success between great (Parus major) and blue (Cyanistes caeruleus) tits in Belgium and examined if forest fragmentation affects these parameters. Analysis of 70 great tit and 34 blue tit eggshells revealed a similar microbiota composition (Enterobacteriaceae, Lactobacillus spp., Firmicutes and Bacteroidetes), but higher bacterial loads in great tits. Forest fragmentation was not identified as an important explanatory variable. Although a significant negative correlation between hatching success and bacterial load on the eggshells in great tits corroborates microbial pressure to be a driver of embryonic mortality, the overall hatching success was only marginally lower than in blue tits. This may be explained by the significantly higher levels of lysozyme and IgY in the eggs of great tits, protecting the embryo from increased infection pressure. Our results show that immune investment in eggs is suggested to be a species-specific adaptive trait that serves to protect hatchlings from pathogen pressure, which is not directly linked to habitat fragmentation.

Evidence for sexual conflict over major histocompatibility complex diversity in a wild songbird.

Sex differences in parasite load and immune responses are found across a wide range of animals, with females generally having lower parasite loads and stronger immune responses than males. Intrigued by these general patterns, we investigated if there was any sign of sex-specific selection on an essential component of adaptive immunity that is known to affect fitness, the major histocompatibility complex class I (MHC-I) genes, in a 20-year study of great reed warblers. Our analyses on fitness related to MHC-I diversity showed a highly significant interaction between MHC-I diversity and sex, where males with higher, and females with lower, MHC-I diversity were more successful in recruiting offspring. Importantly, mean MHC-I diversity did not differ between males and females, and consequently neither sex reached its MHC-I fitness optimum. Thus, there is an unresolved genetic sexual conflict over MHC-I diversity in great reed warblers. Selection from pathogens is known to maintain MHC diversity, but previous theory ignores that the immune environments are considerably different in males and females. Our results suggest that sexually antagonistic selection is an important, previously neglected, force in the evolution of vertebrate adaptive immunity, and have implications for evolutionary understanding of costs of immune responses and autoimmune diseases.

Health hazards to wild birds and risk factors associated with anthropogenic food provisioning.

Provision of supplementary food for wild birds at garden feeding stations is a common, large-scale and year-round practice in multiple countries including Great Britain (GB). While these additional dietary resources can benefit wildlife, there is a concomitant risk of disease transmission, particularly when birds repeatedly congregate in the same place at high densities and through interactions of species that would not normally associate in close proximity. Citizen science schemes recording garden birds are popular and can integrate disease surveillance with population monitoring, offering a unique opportunity to explore inter-relationships between supplementary feeding, disease epidemiology and population dynamics. Here, we present findings from a national surveillance programme in GB and note the dynamism of endemic and emerging diseases over a 25-year period, focusing on protozoal (finch trichomonosis), viral (Paridae pox) and bacterial (passerine salmonellosis) diseases with contrasting modes of transmission. We also examine the occurrence of mycotoxin contamination of food residues in bird feeders, which present both a direct and indirect (though immunosuppression) risk to wild bird health. Our results inform evidence-based mitigation strategies to minimize anthropogenically mediated health hazards, while maintaining the benefits of providing supplementary food for wild birds.This article is part of the theme issue 'Anthropogenic resource subsidies and host-parasite dynamics in wildlife'.

Purifying selection and concerted evolution of RNA-sensing toll-like receptors in migratory waders.

Migratory birds encounter a broad range of pathogens during their journeys, making them ideal models for studying immune gene evolution. Despite the potential value of these species to immunoecology and disease epidemiology, previous studies have typically focused on their adaptive immune gene repertoires. In this study, we examined the evolution of innate immune genes in three long-distance migratory waders (order Charadriiformes). We analysed two parts of the extracellular domains of two Toll-like receptors (TLR3 and TLR7) involved in virus recognition in the Sanderling (Calidris alba), Red-necked Stint (Calidris ruficollis), and Ruddy Turnstone (Arenaria interpres). Our analysis was extended to 50 avian species for which whole-genome sequences were available, including two additional waders. We found that the inferred relationships among avian TLR3 and TLR7 do not match the whole-genome phylogeny of birds. Further analyses showed that although both loci are predominantly under purifying selection, the evolution of the extracellular domain of avian TLR3 has also been driven by episodic diversifying selection. TLR7 was found to be duplicated in all five wader species and in two other orders of birds, Cuculiformes and Passeriformes. The duplication is likely to have occurred in the ancestor of each order, and the duplicated copies appear to be undergoing concerted evolution. The phylogenetic relationships of wader TLR7 matched those of the five wader species, but that of TLR3 did not. Instead, the tree inferred from TLR3 showed potential associations with the species' ecology, including migratory behaviour and exposure to pathogens. Our study demonstrates the importance of combining immunological and ecological knowledge to understand the impact of immune gene polymorphism on the evolutionary ecology of infectious diseases.

Chickadees Faced with Unpredictable Food Increase Fat Reserves but Certain Components of Their Immune Function Decline.

In winter, temperate resident birds are often faced with periodic low natural food availability. This reduction or unpredictability in resource availability might then have a negative impact on immune function, given that immune system support is highly resource dependent. We investigated the balance between energetic and immune management in captive black-capped chickadees (Poecile atricapilus) by manipulating the predictability of resources. The control group received food ad lib. every day, while the experimental group received a reduced amount of food on random days and food ad lib. on all other days. We measured two key metrics of energetic management (body and fat mass) as well as a suite of immune system components. Compared with control birds, experimental birds maintained significantly higher total body and fat mass, had lower acute phase protein concentrations, and had decreased body temperature and lost more body mass during the fever response following injection with lipopolysaccharides. Interestingly, birds in both groups had similar levels of complement lysis, delayed-type hypersensitivity response (phytohemagglutinin), and primary antibody production (keyhole limpet hemocyanin). This experiment demonstrates that black-capped chickadees strategically increase their fat mass in response to decreased food availability and that this might allow the birds to maintain most of the immune system unaltered, except some of the most costly immune components.

The genome sequence and insights into the immunogenetics of the bananaquit (Passeriformes: Coereba flaveola).

Avian genomics, especially of non-model species, is in its infancy relative to mammalian genomics. Here, we describe the sequencing, assembly, and annotation of a new avian genome, that of the bananaquit Coereba flaveola (Passeriformes: Thraupidae). We produced ∼30-fold coverage of the genome with an assembly size of ca. 1.2 Gb, including approximately 16,500 annotated genes. Passerine birds, such as the bananaquit, are commonly infected by avian malarial parasites (Haemosporida), which presumably drive adaptive evolution of immunogenetic loci within the host genome. In the context of our research on the distribution of avian Haemosporida, we specifically characterized immune loci, including toll-like receptor (TLR) and major histocompatibility complex (MHC) genes. Additionally, we identified novel molecular markers in the form of single nucleotide polymorphisms (SNPs), both genome-wide and within identified immune loci. We discovered nine TLR genes and four MHC genes and identified five other TLR- or MHC- associated genes. Genome-wide, over 6 million high-quality SNPs were annotated, including 568 within TLR genes and 102 in MHC genes. This newly described genome and immune characterization expands the knowledge base for avian genomics and phylogenetics and allows for immune genotyping in the bananaquit, providing tools for the investigation of host-parasite coevolution.

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.

Landscape-scale variation in an anthropogenic factor shapes immune gene variation within a wild population.

Understanding the spatial scale at which selection acts upon adaptive genetic variation in natural populations is fundamental to our understanding of evolutionary ecology, and has important ramifications for conservation. The environmental factors to which individuals of a population are exposed can vary at fine spatial scales, potentially generating localized patterns of adaptation. Here, we compared patterns of neutral and major histocompatibility complex (MHC) variation within an island population of Berthelot's pipit (Anthus berthelotii) to assess whether landscape-level differences in pathogen-mediated selection generate fine-scale spatial structuring in these immune genes. Specifically, we tested for spatial associations between the distribution of avian malaria, and the factors previously shown to influence that distribution, and MHC variation within resident individuals. Although we found no overall genetic structure across the population for either neutral or MHC loci, we did find localized associations between environmental factors and MHC variation. One MHC class I allele (ANBE48) was directly associated with malaria infection risk, while the presence of the ANBE48 and ANBE38 alleles within individuals correlated (positively and negatively, respectively) with distance to the nearest poultry farm, an anthropogenic factor previously shown to be an important determinant of disease distribution in the study population. Our findings highlight the importance of considering small spatial scales when studying the patterns and processes involved in evolution at adaptive loci.

Forests of opportunities and mischief: disentangling the interactions between forests, parasites and immune responses.

Habitat characteristics determine the presence of individuals through resource availability, but at the same time, such features also influence the occurrence of parasites. We analyzed how birds respond to changes in interior forest structures, to forest management regimes, and to the risk of haemosporidian infections. We captured and took blood samples from blackcaps (Sylvia atricapilla) and chaffinches (Fringilla coelebs) in three different forest types (beech, mixed deciduous, spruce). We measured birds' body asymmetries, detected avian haemosporidians, and counted white blood cells as an immune measure of each individual per forest type. We used, to our knowledge for the first time, continuous forest structural parameters to quantify habitat structure, and found significant effects of habitat structure on parasite prevalence that previously have been undetected. We found three times higher prevalence for blackcaps compared with chaffinches. Parasite intensity varied significantly within host species depending on forest type, being lowest in beech forests for both host species. Structurally complex habitats with a high degree of entropy had a positive effect on the likelihood of acquiring an infection, but the effect on prevalence was negative for forest sections with a south facing aspect. For blackcaps, forest gaps also had a positive effect on prevalence, but canopy height had a negative one. Our results suggest that forest types and variations in forest structure influence the likelihood of acquiring an infection, which subsequently has an influence on host health status and body condition; however, responses to some environmental factors are host-specific.

Innate immunity and testosterone rapidly respond to acute stress, but is corticosterone at the helm?

When faced with a stressor, vertebrates can rapidly increase the secretion of glucocorticoids, which is thought to improve the chances of survival. Concurrent changes in other physiological systems, such as the reproductive endocrine or innate immune systems, have received less attention, particularly in wild vertebrates. It is often thought that glucocorticoids directly modulate immune performance during a stress response, but, in many species, androgens also rapidly respond to stress. However, to our knowledge, no study has simultaneously examined the interactions between the glucocorticoid, androgen, and innate immune responses to stress in a wild vertebrate. To address this issue, we tested the hypothesis that the change in plasma corticosterone (CORT) in response to the acute stress of capture and restraint is correlated with the concurrent changes in plasma testosterone (T) and innate immune performance (estimated by the capacity of plasma to agglutinate and lyse foreign cells) in the Abert's Towhee (Melozone aberti). Furthermore, to broaden the generality of the findings, we compared male and female towhees, as well as males from urban and non-urban populations. Acute stress increased plasma CORT, decreased plasma T in males, and decreased innate immune performance, but the increase in CORT during stress was not correlated with the corresponding decreases in either plasma T or innate immunity. By contrast, the plasma T stress response was positively correlated with the innate immune stress response. Collectively, our results challenge the proposition that the glucocorticoid stress response is correlated with the concurrent changes in plasma T, a key reproductive hormone, and innate immunity, as estimated by agglutination and lysis.

Causes and Consequences of Partial Migration in a Passerine Bird.

Many animal species have populations in which some individuals migrate and others remain on the breeding grounds. This phenomenon is called partial migration. Despite substantial theoretical work, empirical data on causes and consequences of partial migration remain scarce, mainly because of difficulties associated with tracking individuals over large spatial scales. We used stable hydrogen isotopes in claw material to determine whether skylarks Alauda arvensis from a single breeding population in the Netherlands had migrated or remained resident in the previous winter and investigated whether there were causes or consequences of either strategy. Age and sex had no influence on the propensity to migrate, but larger individuals were more likely to be residents. The wintering strategy was not fixed within individuals. Up to 45% of individuals measured in multiple years switched strategies. Reproductive parameters were not related to the wintering strategy, but individuals that wintered locally experienced lower future return rates, and this was directly correlated with two independent measures of immune function. Our results suggest that partial migration in skylarks is based neither on genetic dimorphism nor on an age- and sex-dependent condition. Instead, the wintering strategy is related to structural size and immune function. These new insights on causes and consequences of partial migration advance our understanding of the ecology, evolution, and coexistence of different life-history strategies.

Blood-feeding ectoparasites as developmental stressors: Does corticosterone mediate effects of mite infestation on nestling growth, immunity and energy availability?

How resources are distributed to growth and self-maintenance early in life is likely to impact survival and reproduction. Early resource allocation decisions may be particularly critical in altricial birds, as they have rapid developmental trajectories, and may be highly susceptible to environmental factors that can perturb development. The aim of this study was to determine if blood-feeding ectoparasites act as developmental stressors in European starling (Sturnus vulgaris) nestlings, driving a trade-off between growth and immunity. We hypothesized that because ectoparasites compete for resources they would induce growth-immunity trade-offs in parasitized nestlings. We also tested the hypothesis that changes in plasma corticosterone mediate the effects of ectoparasites on growth and immunity. Throughout development we assessed between-nest variation in ectoparasite density, measured growth, and a variety of blood parameters, including plasma corticosterone. We also assessed immune function across development. We found that nestlings from nests with high levels of ectoparasites were smaller, had elevated blood glucose, lower hematocrit levels, and appeared to engage in compensatory growth prior to fledging. They also had elevated innate immune responses early, but reduced responses later relative to nestlings from nests with low levels of ectoparasites. Plasma corticosterone was not affected by ectoparasite load, but did increase with nestling age. Overall, we find evidence that ectoparasites are developmental stressors that affect growth-immunity trade-offs, but their effects do not appear to be mediated by changes in circulating levels of corticosterone.

Empirical evidence of cold stress induced cell mediated and humoral immune response in common myna (Sturnus tristis).

Common myna (Sturnus tristis) is a bird indigenous to the Indian subcontinent that has invaded many parts of the world. At the onset of our investigation, we hypothesized that the immunological profile of myna makes it resistant to harsh/new environmental conditions. In order to test this hypothesis, a number of 40 mynas were caught and divided into two groups, i.e., 7 and 25 °C for 14 days. To determine the effect of cold stress, cell mediated and humoral immune responses were assessed. The macrophage engulfment percentage was significantly (P < 0.05) higher at 25 °C rather than 7 °C either co-incubated with opsonized or unopsonized sheep red blood cells (SRBC). Macrophage engulfment/cell and nitric oxide production behaved in a similar manner. However, splenic cells plaque formation, heterophil to lymphocyte (H/L) ratio, and serum IgM or IgG production remained non-significant. There was a significant increase of IgG antibody production after a second immunization by SRBC. To the best of our knowledge, these findings have never been reported in the progression of this bird's invasion in frosty areas of the world. The results revealed a strengthened humoral immune response of myna and made this bird suitable for invasion in the areas of harsh conditions.

Epaulet size and current condition in red-winged blackbirds: examining a semistatic signal, testosterone, immune function, and parasites.

Some sexually selected signals are thought to convey information about the current condition and genetic/epigenetic quality of the individual signaling, including the ability to resist parasites. However, it is unclear whether semistatic sexual signals that develop periodically and remain stable over protracted periods, such as avian breeding plumage, can relate to measures of current condition and health. We examined a semistatic signal (wing epaulet size) in male red-winged blackbirds (Agelaius phoeniceus) during the breeding season and looked for relationships between this trait and circulating testosterone (T), hematocrit, bacteria-killing ability (BKA) of the blood, and the infection status, richness, and abundance of four functional categories of parasite. We found that epaulet size was positively related to circulating levels of T and ectoparasite infections. We found no relationships between T and parasite infections. In adult males there was a negative relationship between T and BKA, whereas in yearling males there was no relationship. We found no evidence for a general reduction in immunocompetence in males with larger epaulets but rather an increase in susceptibility to specific types of parasites. Our results suggest that semistatic signals can be linked to measures of current condition, and we postulate that these relationships are modulated via activity levels related to breeding-season activities.