Cryptic female choice and other types of post-copulatory sexual selection

Abstract

This chapter discusses sexual selection by cryptic female choice (CFC) and other possible types of selection on traits involved in male-female interactions during and following copulation. Morphological, behavioral, and probably also physiological traits all show the typical earmarks of sexual selection: Puzzlingly extravagant, apparently non-utilitarian design; and rapid divergent evolution. I discuss ways to attempt to distinguish CFC from other possibilities, and their potential overlap. Differentiating narrow-sense from broad-sense male-female conflict may help clear up some current confusion. The most central differences between the leading hypotheses concern the expected effects of selectively granting paternity on a female’s fitness. Unfortunately, convincing tests of these effects have not been feasible due to technical limitations; published claims regarding such measurements must be treated with caution. Several types of data that provide less direct tests, including defensive designs of females, the presence of female sense organs specialized to sense courtship stimuli from males, physical damage inflicted on the female by the male during copulation, and physical male-female struggles, are discussed. Different types of selection may operate simultaneously in some species, and all may be applicable in particular cases; the major questions concern the relative frequencies of species in which each type of selection occurs. The hypotheses nevertheless provide useful theoretical contexts for understanding multiple aspects of reproductive biology. One promising area for future studies, in which arthropods can provide both experimental and comparative data, is the role of non-genitalic male copulatory courtship structures in stimulating or physically coercing females during sexual interactions.