At the time, though, chickens and turkeys were not considered ‘real’ birds – rather they were the artificial product of thousands of years of domestication and selective breeding. But it was here that many of the answers lay, especially with respect to reproductive anatomy and physiology, including the period when a female could be fertilized, the so-called fertile period. In fact, it had been
known for over two thousand years that hens could store sperm and produce viable offspring 2 or 3 weeks after her last copulation, later confirmed by poultry biologists who also showed the time course of fertility (Romanoff, 1960). From the mid 1980s onwards, studies of sperm competition in more and more taxa started to appear, including mammals, fish, amphibia and different invertebrates. Smith’s (1984) JQ1 edited volume, the outcome of a prescient symposium he organized in Tucson in 1980, was a landmark, providing up-to-date information on all major taxonomic groups. The discovery of DNA fingerprinting as a way of detecting extra-pair paternity in birds (Burke & Bruford, 1987) transformed the field, and over the next decades, molecular methods for parentage assignment were developed for a
hypoxia-inducible factor pathway range of taxa. Sperm competition studies progressed along two broad fronts. One made use of the new molecular methods to document
the widespread nature of female promiscuity – eventually showing that true genetic monogamy was the exception rather than the norm among birds – and focusing on the adaptive significance of promiscuity (Griffith, Owens & Thuman, 2002). The other approach focused on mechanisms. I will deal with each in turn. The adaptive significance of behaviour was the essence of the behavioural ecology approach and bird researchers were interested in the number of additional offspring a male fathered through his promiscuity. This question was more difficult to answer than initially expected because in order to measure male reproductive success it was necessary to assign paternity unambiguously 17-DMAG (Alvespimycin) HCl (rather than simply identify genetic mismatches), and this was difficult both in terms of the fieldwork and the molecular methods. In the few studies where this has been done, some males do seem to father more offspring through their extra-pair activities, and of course, some lose paternity. Much more difficult to answer was the question of the adaptive significance of extra-pair copulations for females. The male-biased view of extra-pair behaviour was transformed by a study of black-capped chickadees Poecile atricapillus in which Susan Smith (1988) showed that females actively sought extra-pair partners.