Sexual variation in heritability of body size in The Pied Flycatcher - an experimental approach.

There is increasing evidence that recent climatic warming affects various aspects of ecological communities. Most studies to date have used cross-sectional data in order to relate variation in temperature to population trends and various life history trai ts. However such correlative studies can not tell weather the changes observed are caused by phenotypic plasticity or a change in gene frequencies. Selection acts on the phenotype and will only result in a evolu- tionary response if the phenotypic variati on is at least partly based on underlying additive genetic variation. Therefore if we are to predict any evolutionary response to changes in the environment, we need knowledge about the amount of additive genetic variation expressed in populations. There is also very few that have considered the effect of sex when estimating heritability in different environments. This is both surprising and worrying, because sex- ual differences in heritability may strongly influence evolutionary processes. In the presen t project we use an experimental approach to examine the differences in additive genetic vari- ance in body size among male and female pied flycatcher (Ficedula hypoleuca) raised in different environments. We use a novel design (feeding and clutch size ma nipulation) aimed to separate the influence of maternal effects on heritability on body size in different environments. To our knowledge this is the first experiment to address this question in any detail.