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Eunuchs: The Role of Apyrene Sperm in Lepidoptera?

1984; University of Chicago Press; Volume: 123; Issue: 2 Linguagem: Inglês

10.1086/284200

1537-5323

Robert E. Silberglied, Julian Shepherd, Janis L. Dickinson,

Animal Behavior and Reproduction

Moths and butterflies (Lepidoptera) generally produce two types of spermatozoa: a typical nucleated (eupyrene) spermatozoon and a smaller anucleate (apyrene) spermatozoon. The apyrene sperm often predominate over the eupyrene sperm in an ejaculate and, in the female, they migrate actively to the sperm storage organ, the spermatheca. There they usually degenerate, apparently not playing any role in fertilization of the eggs. Several hypotheses for the function of the apyrene sperm have been proposed. These center around the notions that the apyrene sperm may assist the eupyrene sperm in their migration from the testes in the male to the spermatheca in the female or that they function as a nutritional supplement in the female. No experimental support for these notions has been adduced and observational evidence seems to argue against them. We propose that apyrene sperm may play, at least additionally, a role in competition between rival sperm deposited by different males. They may either eliminate, by displacement or inactivation, eupyrene sperm from previous matings or prevent or delay further mating by the female. Several peculiar attributes of the apyrene sperm support these hypotheses. Their much simplified morphology and frequent large preponderance over the eupyrene sperm, their immediate activation during ejaculation and consequent rapid migration to the spermatheca, suggest they might act to overwhelm any sperm stored there from previous matings. The same attributes would also serve to stuff the spermatheca as efficiently and completely as possible, thus perhaps signaling a successful insemination to the female and thereby reducing her receptivity to further mating. We suggest that apyrene sperm are a morphological manifestation of a more widespread phenomenon wherein accessory sperm may play an important role in sperm competition.