Abstracts (first author)
Interactive effects of paternal genotype and growth environment on offspring condition: a cross-fostering experiment in the pied flycatcher
Conspicuous secondary sexual characters, such as sexually dichromatic plumage traits, are thought to have evolved through sexual selection, because they indicate the genetic or phenotypic quality of the bearer. While directional selection should deplete genetic variation in fitness-related traits, there are many cases where variation is higher than expected. One possible explanation for this is that different phenotypes within a population are adapted to different environmental conditions. The dorsal plumage coloration of pied flycatcher (Ficedula hypoleuca) males varies from almost completely black to dull brown. In addition they have several ornamental patches that also vary greatly in size and shape. We compared the condition and survival of the offspring of male pied flycatchers with different plumage phenotypes under different conditions. In order to create different environmental conditions, we used a partial cross-foster design where the original brood size was pairwise reduced or enlarged by one chick. This design enabled us to separate the effects of offspring genotype from parental effects. Preliminary analysis of the data indicates that there are significant interactions between the phenotype of the biological father (forehead patch size) and environmental conditions (brood manipulation treatment and ambient temperature) on chick condition. This suggests that offspring of different male phenotypes differ in their responses to environmental conditions. Therefore, selection on the trait is likely to be context-dependent and environmental heterogeneity may act as a factor maintaining phenotypic variation.