Mechanisms of antimicrobial defense in avian eggs

Abstract

One of the greatest threats to the survival of avian eggs is the risk of infection by microbes; as such, a large number of parental defense mechanisms have evolved in response to the decreased fitness imposed by microbial infection. The existing literature on this topic has focused largely on the mechanisms of microbial invasion through eggshells and the identification of molecules with antimicrobial properties in eggs of commercial species. However, little is still known about antimicrobial mechanisms in wild birds or how they vary with environmental pressures. This review concentrates on recent findings that shed new light on the role of parental behaviors (including incubation and placement of vegetation with antifungal activity in the nest) and the physical properties of eggshells (including nanometer-scale spheres that prevent microbial attachment) that protect eggs from contamination in high-risk environments. In addition to presenting a summary of current information, we identify evident gaps in knowledge and highlight research avenues for the future.