Repeatability of parental effort in male and female Pied Flycatchers as measured with doubly labeled water

Abstract

Intensity of parental care is one of the critical factors affecting offspring growth and final size and thus is a key variable in life-history evolution. In the study population of Pied Flycatchers (Ficedula hypoleuca), it was previously shown that maternal daily energy expenditure was an important source of variance in offspring size and likelihood of infection by blood parasites. Thus, energy expenditure may be considered a parental-performance effect, and variation among females in the intensity of parental care they provide might itself be influenced by genetic differences, affording the opportunity for evolutionary change. To address whether parental work load is a consistent trait and thus may retain additive genetic variance, the same individuals were scored for mass-independent daily energy expenditure (DEE) across two consecutive breeding seasons, while feeding nestlings close to fledging. While DEE of females was significantly repeatable between years, this was not the case for males. DEE may retain additive genetic variance in females, although its expression may be obscured in males by their less constrained activity budgets and lower confidence of paternity.