Maternal Age-Related Depletion of Offspring Genetic Variance in Immune Response to Phytohaemagglutinin in the Blue Tit (Cyanistes caeruleus)

Abstract

Studies examining age-specific patterns in genetic variance have focussed primarily on changes in the genetic variance within cohorts. It remains unclear whether parental age may affect the genetic variance among offspring. To date, such an effect has been reported only in a single study performed in a wild bird population. Here, we provide experimental evidence that the additive genetic variance (V_A) observed among offspring may be related to parental age in a wild passerine-the blue tit (Cyanistes caeruleus). To separate genetic and environmental components of phenotypic variance in nestling body size and immune function we cross-fostered nestlings between pairs of broods born to young and old mothers and used an animal model to estimate V_A. We show that the genetic variance in immune response to phytohaemagglutinin (PHA) and body weight among offspring depends on maternal age. V_A in response to PHA appeared to be lower among nestlings of older mothers. Such a tendency was not observed for tarsus length. We argue that the lower V_A may result either from depletion of additive genetic variation due to selection acting on parents across age classes or from environmental effects confounded with parental age. Thus, our study suggests that parental age may significantly affect estimates of quantitative genetic parameters in the offspring.

Keywords: Age; Blue tit; Genetic interaction; Heritability; Immunocompetence.

Fig. 1

Schematic illustration of experimental design. Solid-line rectangles depict individual nests, between which nestlings where cross-fostered (arrows). Full and dashed circles depict individual experimental nestlings, open circles depict donor nestlings used in the brood-size manipulation experiment. Note that for clarity only six experimental nestlings are depicted for each clutch, a number that differed depending on the original clutch-size

Fig. 2

Age-specific differences in heritabilities (with their SE’s) of tarsus length, body mass and PHA response. Values for body mass and tarsus length were extracted from unsupported age-specific models to allow direct comparisons with PHA response