Genetic and environmental components of the colour of mouth, flanges and skin in spotless starling (Sturnus unicolor)

Abstract

The begging display of avian nestlings includes visual and acoustical signals of their phenotypic condition and needs that parents use to, for instance, decide feeding effort and the individual nestlings to feed. Flamboyant colouration of mouths and flanges, as well as the UV colouration of nestlings’ skin, are pivotal characters in parent-offspring communication. Coloration of begging related traits should therefore be phenotypically plastic. However, these traits vary interspecifically in association with species-specific parental visual characteristics and light conditions of nests and, thus, should also have a genetic component allowing its evolution. As far as we know, the genetic component of begging related trait has never been quantified. Here, do so in a spotless starling (Sturnus unicolor) population by comparing phenotypes of 10 days old nestlings that were cross-fostered among 15 pairs of nests at the time of hatching. We measured the colour of the mouth, flanges and skin with a spectrophotometer and estimated different chromatic and achromatic colour components, either, considering or not characteristics of the starling colour vision. Results confirm a strong environmental component for most colours and measured traits of nestlings, while evidence of genetic components appeared mainly for coloration of nestling traits that were known to reflect its phenotypic quality (ultraviolet colour of skin, and yellow-red colouration of mouths and/or flanges). Interestingly, we also detected a genetic component of visual contrasts that considered parental visual characteristics, which further suggest that the evolution of these colourations is driven by parents and parental favouritism toward nestlings of particular colouration.