The cuticle modulates ultraviolet reflectance of avian eggshells

ABSTRACT Avian eggshells are variedly coloured, yet only two pigments, biliverdin and protoporphyrin IX, are known to contribute to the dramatic diversity of their colours. By contrast, the contributions of structural or other chemical components of the eggshell are poorly understood. For example, unpigmented eggshells, which appear white to the human eye, vary in their ultraviolet (UV) reflectance, which may be detectable by birds. We investigated the proximate mechanisms for the variation in UV-reflectance of unpigmented bird eggshells using spectrophotometry, electron microscopy, chemical analyses, and experimental manipulations. We specifically tested how UV-reflectance is affected by the eggshell cuticle, the outermost layer of most avian eggshells. The chemical dissolution of the outer eggshell layers, including the cuticle, increased UV-reflectance for only eggshells that contained a cuticle. Our findings demonstrate that the outer eggshell layers, including the cuticle, absorb UV-light, probably because they contain higher levels of organic components and other chemicals, such as calcium phosphates, compared to the predominantly calcite-based eggshell matrix. These data highlight the need to examine factors other than the known pigments in studies of avian eggshell colour

Intra-specific brood parasitism revealed by DNA micro-satellite analyses in a sub-oscine bird, the vermilion flycatcher

Extra-pair reproduction is known to occur in many avian species. However, among passerines, the majority of studies on extra-pair reproduction have been carried out in oscine birds from temperate regions. Conversely, sub-oscines species, and particularly, species that inhabit tropical regions, have been studied to a much lesser extent. Given that a majority of avian species live in the tropics, it is important to study more tropical and sub-oscine species to have a more accurate picture of the rates of extra-pair reproduction among passerines, and a better understanding of the adaptive function of extra-pair reproduction in birds. Tropical species differ from temperate species in several ecological and life history traits, that may influence the occurrence of different modes of extra-pair reproduction and their prevalence. In this study we asked whether extra-pair reproduction occur in a sexually dimorphic and socially monogamous sub-oscine, the vermilion flycatcher (Pyrocephalus rubinus). We report cases of extra-pair paternity, extra-pair maternity and intra-specific brood parasitism, and discuss our results in the view of other studies with passerines.</p