Evolution and expression of genetic variation in nestling traits

Environmental conditions experienced during early life are known to impact upon the development of passerinenestlings, as well as on their performance and fitness as adults. Nevertheless, little is yet known about the relative importanceof different types of maternal, environmental and genetic effects as proximate determinants of variation in nestling traits, andin particular, how the relative importance of these components is affected by the characteristics of the growth environment.Evidence from a number of studies suggests that the expression of both genetic and maternal effects can be highly environmentdependent,together with their impact upon fitness variation among individuals. Again relatively little is known about howselection acts upon this variation. According to one popular scenario, selection acts mainly on environmental, not genotypicvariation. Using data from a long-term study of collared flycatchers (Ficedula albicollis) from the Swedish island of Gotland,we demonstrate that: (1) common environmental/parental effects have a strong influence on variation in nestling traits, and (2)different traits are affected differentially by early vs late effects. We further demonstrate that (3) selection acts on genetic, aswell as environmental, variation. These results suggest that common environmental/parental effects may be more importantsources of variation in nestling traits than previously acknowledged, and that the time-window for these effects differs fordifferent traits. Furthermore, our analyses reinforce the conclusion that selection on environmental deviations cannot aloneexplain the lack of expected selection responses in heritable nestling traits under directional selection.

Juha Merila, Loeske E.B. Kruuk, B.C. Sheldon, Acta Zoologica Sinica 52(Supplement): 666-669, 2006