Immune genotypes, immune responses, and survival in a wild bird population.

Individuals vary in their immune genotype, inbreeding coefficient f, immune responses, survival to adulthood, and adult longevity. However, whether immune genes predict survival or longevity, whether such relationships are mediated through immune responses, and how f affects immune genotype remain unclear. We use a wild song sparrow (Melospiza melodia) population in which survival to adulthood, adult longevity, and f were measured precisely, and in which immune responses have previously been assessed.

Stronger population differentiation at infection-sensing than infection-clearing innate immune loci in songbirds: Different selective regimes for different defenses.

Parasite-mediated selection is widespread at loci involved in immune defense, but different defenses may experience different selective regimes. For defenses involved in clearing infections, purifying selection favoring a single most efficacious allele likely predominates. However, for defenses involved in sensing and recognizing infections, evolutionary arms races may make positive selection particularly important.

Preen gland microbiota of songbirds differ across populations but not sexes.

Metabolites produced by symbiotic microbes can affect the odour of their hosts, providing olfactory cues of identity, sex or other salient features. In birds, preen oil is a major source of body odour that differs between populations and sexes. We hypothesized that population and sex differences in preen oil chemistry reflect underlying differences in preen gland microbiota, predicting that these microbes also differ among populations and between the sexes.

Many loci make light work: High individual diversity despite low population diversity and random mating at class I MHC in a Critically Endangered island songbird.

Multi-cellular organisms are under constant attack from parasites, making immune defence a critical aspect of fitness. In vertebrate animals, genes of the major histocompatibility complex (MHC) determine the breadth of pathogens to which individuals can respond. Having many MHC alleles can confer better protection against infectious disease, and balancing selection at MHC is widespread.

"Balancing" balancing selection? Assortative mating at the major histocompatibility complex despite molecular signatures of balancing selection.

In vertebrate animals, genes of the major histocompatibility complex (MHC) determine the set of pathogens to which an individual's adaptive immune system can respond. MHC genes are extraordinarily polymorphic, often showing elevated nonsynonymous relative to synonymous sequence variation and sharing presumably ancient polymorphisms between lineages. These patterns likely reflect pathogen-mediated balancing selection, for example, rare-allele or heterozygote advantage.

Wax Ester Composition of Songbird Preen Oil Varies Seasonally and Differs between Sexes, Ages, and Populations.

Chemical signaling has been well studied in invertebrates and mammals but less so in birds, due to the longstanding misconception that olfaction is unimportant or even non-existent in this taxon. However, recent findings suggest that olfaction plays an important role in avian mate choice and reproductive behavior, similar to other taxa. The leading candidate source for compounds involved in avian chemical communication is preen oil, a complex mixture secreted from the uropygial gland.

Purifying Selection in the Toll-Like Receptors of Song Sparrows Melospiza melodia.

Variation in immune gene sequences is known to influence resistance to infectious diseases and parasites, and hence survival and mate choice, across animal taxa. Toll-like receptors (TLRs) comprise one essential gene family in the vertebrate innate immune system and recognize evolutionarily conserved structures from all major microorganism classes. However, the causes and consequences of TLR variation in passerine birds remain largely unexplored.

Exposing migratory sparrows to Plasmodium suggests costs of resistance, not necessarily of infection itself.

Migratory birds move through multiple habitats and encounter a diverse suite of parasites. This raises concern over migrants' role in transporting infectious disease between breeding and wintering grounds, and along migratory flyways. Trade-offs between flight and immune defenses could interfere with infected individuals' migratory timing and success, potentially affecting infection dynamics.

Immune profiles vary seasonally, but are not significantly related to migration distance or natal dispersal, in a migratory songbird.

A central tenet of ecoimmunology is that an organism's environment shapes its optimal investment in immunity. For example, the benefits of acquired (relatively pathogen specific) versus innate (nonspecific) immune defenses are thought to vary with the risk of encountering familiar versus unfamiliar pathogens. Because pathogen communities vary geographically, individuals that travel farther during seasonal migration or natal dispersal are predicted to have higher exposure to novel pathogens, and lower exposure to familiar pathogens, potentially favoring investment in innate immunity.

Song sparrows have a home-field advantage in defending against sympatric malarial parasites.

Hosts and parasites interact on both evolutionary and ecological timescales. The outcome of these interactions, specifically whether hosts are more resistant to their local parasites (sympatric) than to parasites from another location (allopatric), is likely to affect the spread of infectious disease and the fitness consequences of host dispersal. We conducted a cross-infection experiment to determine whether song sparrows () have an advantage in dealing with sympatric parasites.

Testosterone, migration distance, and migratory timing in song sparrows Melospiza melodia.

In seasonally migratory animals, migration distance often varies substantially within populations such that individuals breeding at the same site may overwinter different distances from the breeding grounds. Shorter migration may allow earlier return to the breeding grounds, which may be particularly advantageous to males competing to acquire a breeding territory. However, little is known about potential mechanisms that may mediate migration distance.

Early-life stress has sex-specific effects on immune function in adult song sparrows.

Multiple components of the immune system are modulated by environmental factors, including exposure to stressors. In particular, chronic stressors can impair development of the immune system, leading to alterations in immune function in adulthood. While these effects have been well established in mammals, less is known about how developmental stress modulates immunity in nonmammalian species.

Developmental stress, condition, and birdsong: a case study in song sparrows.

Sexual-selection theory posits that ornaments and displays can reflect a signaler's condition, which in turn is affected both by recent and developmental conditions. Moreover, developmental conditions can induce correlations between sexually selected and other traits if both types of traits exhibit developmental phenotypic plasticity in response to stressors. Thus, sexually selected traits may reflect recent and/or developmental characteristics of signalers.

Developmental timing of signals affects information content: song complexity but not consistency reflects innate immune strategy in male song sparrows.

In short-lived animals, innate immunity is an important component of fitness and quality. Although receivers cannot generally assess a signaler's immune function directly, sexually selected displays such as birdsong may reflect past or current condition. We investigated the degree to which song complexity and consistency, thought to reflect condition over different developmental timescales, predict multiple aspects of innate immunity in male song sparrows (Melospiza melodia).

Developmental programming of the HPA and HPG axes by early-life stress in male and female song sparrows.

Variation in early environmental conditions can have long-term effects on physiology and behavior, a process referred to as developmental programming. In particular, exposure to early-life stressors can have long-term effects on regulation of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes. Although these effects have been well documented in mammals, less is known about how early-life stress affects regulation of these endocrine systems in non-mammalian species.

HPA axis regulation, survival, and reproduction in free-living sparrows: Functional relationships or developmental correlations?

A growing body of theoretical and empirical work has addressed the relationship between hypothalamus-pituitary-adrenal (HPA) function and fitness. For example, the corticosterone (CORT)-fitness and CORT-condition hypotheses predict that baseline and/or stress-induced levels of glucocorticoids should relate to fitness, and recent empirical studies have reported relationships between HPA function and fitness-related sexually selected traits. Here we introduce a framework for evaluating whether such relationships reflect functional relationships or developmental correlations.

Developmental stress has sex-specific effects on nestling growth and adult metabolic rates but no effect on adult body size or body composition in song sparrows.

Variation in the prenatal and postnatal environments can have long-term effects on adult phenotype. In humans and other animals, exposure to stressors can lead to long-term changes in physiology. These changes may predispose individuals to disease, especially disorders involving energy metabolism.

Regulation of the HPA axis is related to song complexity and measures of phenotypic quality in song sparrows.

Regulation of the hypothalamic-pituitary-adrenal (HPA) axis is a key component of the vertebrate stress response. Prior studies have found that variation in HPA responses were correlated to measures of fitness and physiological condition. In addition, sexually-selected traits have also been found to correlate to measures of condition.

Local song elements indicate local genotypes and predict physiological condition in song sparrows Melospiza melodia.

Geographical variation in birdsong is taxonomically widespread and behaviourally salient, with females often preferring local over non-local song. However, the benefits associated with this preference remain poorly understood. One potential explanation is that song may reflect a male's place of origin and thus allow females to obtain genes well adapted to the local environment.

Estradiol modulates brainstem catecholaminergic cell groups and projections to the auditory forebrain in a female songbird.

In songbirds, hearing conspecific song induces robust expression of the immediate early gene zenk in the auditory forebrain. This genomic response to song is well characterized in males and females of many species, and is highly selective for behaviorally relevant song. In white-throated sparrows, the selectivity of the zenk response requires breeding levels of estradiol; we previously showed that in non-breeding females with low levels of plasma estradiol, the zenk response to hearing song is no different than the response to hearing frequency-matched tones.

Song repertoire size varies with HVC volume and is indicative of male quality in song sparrows (Melospiza melodia).

Complex birdsong is a classic example of a sexually selected ornamental trait. In many species, females prefer males with large song repertoires, possibly because repertoire size is limited by the size of song control nuclei which reflect developmental success. We investigated whether song repertoire size was indicative of brain area and male quality in song sparrows (Melospiza melodia) by determining if repertoire size was related to the volume of song control nucleus HVC, as well as several morphological, immunological and genetic indices of quality.

Parasite-mediated heterozygote advantage in an outbred songbird population.

Coevolution with parasites is thought to maintain genetic diversity in host populations. However, while there are sound theoretical reasons to expect heterozygosity and parasite resistance to be related, this pattern has generally been shown only in inbred laboratory and island populations. This leaves doubt as to whether parasite-mediated selection for genetic diversity is in fact a general process.

Effects of day-length and food availability on food caching, mass and fat reserves in black-capped chickadees (Poecile atricapillus).

Many animals seasonally change energy stores such as food caches and fat deposits. Two factors that potentially influence energy stores are changes in day-length and food availability. We investigated food storing and fat levels in black-capped chickadees to determine how they are affected by changes in duration of light period and duration of food availability.