Sexuelle Selektion und die Evolution von Kopulationen außerhalb des Paarbundes = sexual selection and the evolution of extra-pair copulation : Spielregeln der Weibchen : rules of the game from the females' point of view

In view of Darwin's fundamental thesis on sexual selection, which appeared in 1871, it is no longer a secret that a peacock can spread his tail because the females want it that way. It is generally acknowledged that the peacock is polygamous; whichever male has the most attractive plumage wins the most females and therefore achieves the greatest reproductive success. It is due to selective breeding by the females, i.e. "female choice" that the males have become what they are today. In monogamous mating systems, however, the source of striking colouring in males could not be explained the same way until evidence for the common occurrence of "extra-pair copulation" became more accepted. This mating behaviour offers an explanation of how certain males, even in monogamous species, can produce more offspring than others. Only in recent years was it recognised that it is often the females which play the active role in the initiation of extra-pair copulation. What fitness gains can the females expect to achieve through this behaviour? This review commences with an introduction to fundamental theories of sexual selection. Progressing from this, the current discussion of extra-pair copulation (EPC) is reviewed. Conceivable fitness gains for the females, which may have resulted in the evolution of EPC, are summarised. A connection is noted between the various possible fitness gains in their effect on the "total reproductive value" of the females. The necessity of considering all of these theories from a more general perspective, without having to dismiss any explanations from the outset, is made clear Gowaty's "constrained female hypothesis" (1996) is one example in which this has been achieved. This hypothesis proposes that females can be obliged to engage in EPC in order to obtain any kind of extra fitness gain, since they are often constrained in their choice of a partner (e.g. by the males themselves). In conclusion, possible directions are suggested for the testing of these hypotheses in field studies; in future more emphasis should be put on intrinsic quality differences between the females while investigating their mating behaviour.