Is eggshell pigmentation a condition-dependant strategy? Implications for egg crypsis in Japanese quail.

摘要

Avian eggshell colouration fulfills multiple adaptive functions, including egg camouflage. The potential role of the two main eggshell pigments in oxidative stress, biliverdin and protoporphyrin, may be behind a relationship between female immunocompetence and eggshell pigment investment strategies. In this study, environmental conditions were manipulated during different life cycle stages, via a variety of methods, including food-restriction and stress hormone exposure in female Japanese quails (Coturnix coturnix japonica), in order to experimentally test the condition-dependence of eggshell pigmentation, and to give first insights into the possible implications for egg crypsis. I demonstrated that eggshell pigmentation strategy is not only affected by female current body condition, but is also shaped by its early life experience such as exposure to stress, and that eggshell colouration is a key factor involved in egg crypsis in Japanese quail. Eggshell colour and maculation were both independently affected by breeding conditions; which stresses the complexity of the relationship between eggshell pigment concentrations and its appearance. My findings imply that eggshell appearance is a female extended phenotypic trait, and that trade-offs between eggshell pigmentation and immune-functions may lead to inter-females differences in their ability to maximise egg crypsis.