Sperm competition and fertilization success

Much of our understanding of the reproductive physiology of birds is derived from research by poultry biologists. Starting in the 1970s behavioural ecologists began to explore the evolutionary consequences of female promiscuity across a range of taxa, but mainly insects and birds, focusing on the fact that, if females copulate with two or more males in a single reproductive cycle, selection will favour the male that fertilizes the female's ova. Since male-male competition and female choice can continue after copulation, this area of research is known as post- copulatory sexual selection and comprises both sperm competition and cryptic female choice. Behavioural ecologists concentrated initially on functional (ultimate) issues (the adaptive significance of particular traits) but later also started to address mechanistic (proximate) questions. Information on the reproductive biology of domesticated birds from poultry research and collaboration between poultry biologists and behavioural ecologists provided an unusually productive opportunity for understanding some of the mechanisms of post- copulatory sexual selection in birds within an evolutionary context. We review those studies to identify the factors that determine male and female reproductive success. © CAB International 2009.