EVIDENCE FOR LOCK-AND-KEY MECHANISMS IN THE INTERNAL GENITALIA OF THEAPAMEA MOTHS (LEPIDOPTERA, NOCTUIDAE)

Fifty of the fifty-six species of the genus Apamea known from North Am erica and three Palaearctic species were analysed for lock-and-key cha racters in their internal genitalia, mainly in the male vesica and the female bursa copulatrix. There were an average of 4.5 such characters per species, structurally corresponding in the two sexes. Anatomicall y they form a postcopulatory but prezygotic isolation mechanism. In so me closely related species, the internal genitalia are very similar, b ut these species have a precopulatory isolation mechanism in the prese nce or absence of male abdominal coremata. Closely related species did not have more lock-and-key characters than unrelated species, which i s taken to indicate absence of character displacement. The anatomical distribution of the lock-and-key characters was examined and the organ s of eight species are illustrated. The lock-and-key hypothesis has be en abandoned by several earlier authors but mainly on consideration of external genitalia. In Apamea the invariable functional correspondenc e between sexes in the sperm transferring organs, and the overall spec ies-specificity of characters but non-existence of interspecific diffe rences under a precopulatory mechanism indicate that (a) lock-and-keys are functioning and (b) they act as isolation mechanisms. Alternative hypotheses of genitalic evolution are reviewed.