No abstract

Major histocompatibility complex (MHC) genes encode proteins involved in the recognition of parasite-derived antigens. Their extreme polymorphism is presumed to be driven by co-evolution with parasites. Host-parasite co-evolution was also hypothesized to optimize within-individual MHC diversity at the intermediate level. Here, we use unique data on lifetime reproductive success (LRS) of female collared flycatchers to test whether LRS is associated with within-individual MHC class II diversity. We also examined the association between MHC and infection with avian malaria. Using 454 sequencing, we found that individual flycatchers carry between 3 and 23 functional MHC class II B alleles. Predictions of the optimality hypothesis were not confirmed by our data as the prevalence of blood parasites decreased with functional MHC diversity. Furthermore, we did not find evidence for an association between MHC diversity and LRS.

Although immune function usually declines with age in humans and captive animals, little is known about whether immune function deteriorates with age in natural populations. Here we present evidence for such an age‐related deterioration in humoral immune function from a wild population of the Collared Flycatcher (Ficedula albicollis). In this study, young (1‐year old), mid‐age (3‐year old) and old (5–6‐year old) females were challenged with a nonpathogenic antigen, sheep red blood cells (SRBC), while provisioning their nestlings. The level of antibodies against SRBC was measured thereafter. Old females showed markedly lower humoral immune response and produced fledglings of lower body mass in comparison with the other two age classes. Moreover, the age classes differed in the relationship between immune response and fledgling body mass with mid‐age females showing a significant positive relationship while the relationship was negative but nonsignificant among young and old females. The results are discussed in light of existing theories of optimal resource allocation, ageing and the theory of terminal investment.

Differential reproductive investment by the mother can critically influence offspring development and phenotype, and strong selection is therefore expected to act on such maternal effects. Although a genetic basis is a prerequisite for phenotypic traits to respond to selection and thus to evolve, we still know very little about the extent of heritable variation in maternal effects in natural populations. Here, we present the first estimates of intrafemale repeatability across breeding seasons and estimates of heritability of hormonemediated maternal effects in a wild population of collared flycatchers (Ficedula albicollis). We found that maternal yolk testosterone (T) concentrations, yolk mass, and egg mass were moderately to highly repeatable within females across years, whereas intrafemale consistency of maternal yolk androstenedione (A4) deposition was low yet statistically significant. Furthermore, maternal yolk T transfer, yolk mass, and egg mass were significantly heritable, whereas yolk A4 transfer was not. These results strongly suggest that two major maternal yolk androgens are differentially regulated by genes and the environment. Selection on heritable variation in maternal yolk T deposition has the potential to shape the rate and direction of phenotypic change in offspring traits and can thereby accelerate or impede the response to selection in natural populations.

This paper aims at partitioning genetic and environmental contribution to the phenotypic variance in nestling immune function measured with the hypersensitivity test after inoculation with phytohaemagglutinin. A cross‐fostering experiment with artificial enlargement of some broods was conducted. Variation in nestling immune response was related to their common origin, which suggests heritable component of cell‐mediated immunity. A common rearing environment also explained a significant part of variation. However, deterioration of rearing conditions as simulated by enlargement of brood size did not affect nestling immunocompetence, although it affected nestling body mass. Variation in body mass explained some of the variation in immune response related to rearing environment, which means that growth is more sensitive to the shifts in rearing conditions than the development of immune function. Heritable variation in immune response suggests that there should be potential for selection to operate and the micro evolutionary changes in immunity of flycatcher nestlings are possible.