ABSTRACT

Females can have important, but often underestimated effects on the likelihood that any given copulation will result in fertilization of their eggs. Examples of at least 15 different processes that occur during or after intromission, and in which females can selectively favor one male's chances of paternity over those of another, are given for insects and arachnids.

Two general phenomena suggest that such ‘cryptic’ female choice is not a rare biological curiosity, but rather a widespread and common phenomenon. Male courtship behavior in insects and spiders often (probably usually) begins or continues after intromission has occurred; the most likely explanation of this otherwise paradoxical behavior is that it serves to influence cryptic female choice. In addition, male seminal products in insects and ticks commonly influence several aspects of female reproductive physiology. Several kinds of evidence indicate that these male products have evolved under sexual selection, usually as triggering mechanisms rather than as nutrients. They may constitute ‘chemical genitalia’ that influence cryptic female choice.

Several widely held ideas about sexual selection and courtship should be modified to take into account the fact that females are less passive in male–female interactions than has previously been supposed.