Causes and consequences of quantitative trait variation for reproductive performance in hole nesting birds

Abstract: This thesis examines the causes and consequences of environmental variability and individual morphological differences on breeding success and survival in three hole nesting birds.An analysis of directional and stabilising natural selection in Collared Flycatchers (Ficedula albicollis) suggested that forces of selection acting on quantitative traits are weak and cannot explain the observed sexual size dimorphism (SSD) in this species. The hypothesis that food niche differentiation might enhance reproductive success and explain the evolution of SSD was not supported by studies of Great and Blue Tits (Parus major and P. caeruleus). Analysis of natural selection on nestling body condition in Blue Tits revealed weak positive directional selection on this trait. This observation is consistent with the moderate heritability (h2 = 0.4) of body condition uncovered by a quantitative genetic analyses.Territorial quality had a greater effect on breeding success than parental quality in Blue Tits. Nevertheless male, but not female quality, affected offspring condition. Climatic fluctuations were found to affect laying date and male tarsus length in Collared Flycatchers. The effects of individual-specific features were found to be more important than environmental factors in determining laying date and variation in morphological traits in this species. The high degree of concordance between cross-sectional and longitudinal analyses of the effect of environmental factor on laying date suggests the observed response can be explained entirely in terms of phenotypic plasticity.