Traditional population genetics theory assumed that at some level in the hierarchy of genetic diversity there existed 'demes' in which males and females mate at random. Polygynous mating systems or individual variance in reproductive success were considered complications which altered estimates of effective population size and the calculation of F-statistics. Recent breeding group models bridge the gap between behavioural ecology and population genetics, and illustrate how genetic approaches can aid the study of mating systems, and vice versa.
At the practical level, molecular genetic tools such as DNA fingerprinting and microsatellites have revolutionized our understanding of the fitness consequences of different mating behaviours. We describe how the molecular methods we have used in studies of avian mating systems illustrate two important practical challenges. The first example uses the tree swallow to describe the difficulties of working with a large, open population of potential fathers. The second example summarizes work on two Australian miner species, which breed cooperatively. The practical challenges came in dealing with genetic relatedness of helpers at nests, both to explain helping, and to assign parentage in the few cases it was necessary. The fact that helpers were kin, coupled with some inbreeding, revealed the limits of even the most modern molecular approaches to mating systems. Traditional behavioural observations of known individuals will often still be needed to understand the complex pedigrees in such systems.
On the theoretical side, it is increasingly apparent that evolutionary explanations for the diversity of mating systems will have to be supported by rigorous genetic models. Most passerines were assumed to be monogamous, yet we now know there is little correspondence between their behavioural and genetic mating systems. It appears that EPP is often under female control, and much effort is being devoted to understanding how females distinguish between behavioural and genetic mates. Genetic explanations for EPP include the genetic diversity, genetic compatibility and good genes models. Our work with chickadees allows us to predict which males are likely to be chosen by females for EPP, but only a small number of other studies have found any correlates of male EPP success. Often genetic explanations of EPP are not well articulated, and there remains a real need to determine if behavioural ecologists are proposing genetical theories which are likely to apply in real populations in a reasonable amount of evolutionary time.