Forced Matings in Natural Populations of Drosophila.

Forced mating has been reported for a number of vertebrate and invertebrate taxa. The implications of forced copulation for mating system evolution, however, has received the greatest consideration for birds (Gowaty and Buschhaus 1998). Insect species in which females mate before full maturation represent a different slant on forced mating. Some lepidoptera, for example, exhibit the unusual phenomenon of pupal mating, in which males are attracted to uneclosed females and mate with them before their emergence (Brower 1997). The degree to which females in pupal-mating species exercise mate choice is questionable. Species of the genus Drosophila, especially Drosophila melanogaster, provide one of the most popular model systems for the study of sexual selection and sexual isolation. Studies of reproductive behavior in Drosophila have commonly assumed that females control whether a mating will take place and with whom. Exceptions include conditions of artificially high density, such as in laboratory population cages (Burnet and Connolly 1974), in which females, unlike under natural conditions, cannot escape the advances of courting males. The assumption of female control is reflected in the names of the experimental paradigms employed, such as the “female choice” design and the “no choice” design. Laboratory studies always employ sexually mature flies that are several days old. While the merits of one design over another depend upon the question being addressed, all have two common assumptions. The first assumption is that under the conditions of the tests, flies