Abstract
Most male lepidopterans produce fertile eupyrene sperm and non-fertile apyrene sperm, both of which are transferred to the female in a spermatophore during mating. Apyrene sperm outnumbers eupyrene sperm and both sperm types migrate from the bursa copulatrix to the spermatheca after mating. While eupyrene sperm are maintained in the spermatheca until oviposition, the number of apyrene sperm decreases with time. It is unclear whether apyrene sperm disappear from all sperm storage organs in females because both sperm types are often observed in the spermathecal gland. To investigate this, the numbers of both sperm types were estimated in the spermatheca and spermathecal gland of female Byasa alcinous (a monandrous butterfly) 6, 12, 48, 96, and 192 h after mating terminated. Apyrene sperm arrived in the spermatheca earlier than eupyrene sperm; however, some eupyrene and apyrene sperm migrated to the spermathecal gland from the spermatheca at almost the same time. The number of apyrene sperm reached a peak 12 h after the termination of mating and then decreased with time in both the spermatheca and spermathecal gland. Our results suggest that the role of apyrene sperm might be completed early after arriving in the spermatheca of B. alcinous.
Highlights
Most male lepidopterans produce fertile eupyrene sperm and non-fertile apyrene sperm, both of which are transferred to the female in a spermatophore during mating
Two models to explain the length of the spermathecal gland were compared: the null model (BIC = 170.681, df = 32) had a lower Bayesian information criteria (BIC) value than an alternative model that included forewing length as an explanatory variable (BIC = 173.075, df = 31), indicating that the length of spermathecal gland did not depend on forewing length
Rapid declines in apyrene spermatozoa from the spermatheca have been quantitatively demonstrated in polyandrous species such as Pseudaletia separate[20], Papilio xuthus[19], and Eurema mandarina[12]
Summary
Most male lepidopterans produce fertile eupyrene sperm and non-fertile apyrene sperm, both of which are transferred to the female in a spermatophore during mating. A study of the polyandrous green-veined white butterfly, Pieris napi, by Cook and Wedell supports this h ypothesis[11]: females that store a larger number of apyrene sperm show a lower receptivity for re-mating This hypothesis is more controversial in other species[12,13,14]. Apyrene sperm is necessary for complete dissociations of eupyrene sperm bundles in Bombyx mori[9] This may be one reason for the sterility and failure of sperm migration in B. mori males that produce abnormal apyrene s perm[7,15]. These hypotheses are not mutually exclusive; apyrene sperm could have multiple functions[2]
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