Eupyrene sperm migrates to spermatheca after apyrene sperm in the swallowtail butterfly, Papilio xuthus L. (Lepidoptera: Papilionidae)

Abstract

When swallowtail butterflies, Papilio xuthus, are mated by the hand-pairing method, both types of sperm, eupyrene and apyrene sperm, are transferred from the male to the spermatheca via the spermatophore in the bursa copulatrix. This mechanism is demonstrated by two different kinds of experiments. The first set of experiments employed interrupted copulation, and the second set was examination of the sperm in the spermatophore and spermatheca after the termination of copulation. The sperm was transferred 30 min after the start of copulation. The eupyrene sperm was still in the bundle; the number of the bundles ranged from 9 to 108 (mean, 42.7; n ϭ 27). The bundles were gradually released after the completion of copulation, and the free eupyrene spermatozoa then remained in the spermatophore at least 2 h before migrating to the spermatheca. On the other hand, about 160 000 apyrene spermatozoa were transferred to the spermatophore and remained there for more than 1 h. We observed 11 000 apyrene spermatozoa in the spermatheca 12 h after the completion of copulation, but most of this type of sperm disappeared shortly thereafter. In contrast, the eupyrene sperm arrived in the spermatheca more than 1 day after the completion of copulation and remained there at least 1 week. Therefore, these findings suggest that apyrene sperm migrate from the spermatophore to the spermatheca earlier than eupyrene sperm. Accordingly, if females mated multiply, the time difference might avoid the mixing of sperm. In addition, the predominance of sperm from the last mating session may occur not in the bursa copulatrix but in the spermatheca.

Dynamics of eupyrene and apyrene sperm storage in ovipositing females of the swallowtail butterfly Papilio xuthus (Lepidoptera: Papilionidae)

“…The procedure used for counting sperm is described in detail by Watanabe et al . (1998a,b; 2000). We evaluated the number of both types of spermatozoa that a male delivered to a female by counting the number of spermatozoa in the transferred spermatophore.…”

“…1998b). Watanabe et al . (2000) examined the number of eupyrene and apyrene spermatozoa in the reproductive organ of the female swallowtail butterfly Papilio xuthus (Linnaeus, 1767) after copulation, and counted 10 000 eupyrene and 160 000 apyrene spermatozoa in a single spermatophore and 1500 eupyrene and 10 000 apyrene spermatozoa in the spermatheca.…”

“…(2000) examined the number of eupyrene and apyrene spermatozoa in the reproductive organ of the female swallowtail butterfly Papilio xuthus (Linnaeus, 1767) after copulation, and counted 10 000 eupyrene and 160 000 apyrene spermatozoa in a single spermatophore and 1500 eupyrene and 10 000 apyrene spermatozoa in the spermatheca. Although the bursa copulatrix is capable of elongating with the number and the volume of spermatophores it contains, the spermatheca seems to remain constant in size during the female lifespan, regardless of the number of spermatozoa it contains (Watanabe et al . 2000).…”

“…Watanabe et al . (2000) also described a spermathecal gland leading from the distal end of the spermatheca.…”

Female receptivity in butterflies and moths

“…Apyrene sperm are highly active at ejaculation, whereas eupyrene sperm usually remain in bundles. Apyrene sperm also appear to reach the female's spermatheca before the fertile sperm in both butterflies and moths (Silberglied et al, 1984;Tschudi-Rein and Benz, 1990;Watanabe et al, 2000;Marcotte et al, 2003). Non-fertile sperm seem to be critical to male reproductive success, because males do not decrease investment in apyrene relative to eupyrene sperm when reared on a restricted diet (Gage and Cook, 1994;Cook and Wedell, 1996).…”