Adaptive significance of the mating of autumn-morph females with non-overwintering summer-morph males in the Japanese Common Grass Yellow, Eurema mandarina (Lepidoptera: Pieridae)

Abstract

Autumn-morph adults of the Japanese Common Grass Yellow, Eurema mandarina (de l’Orza), overwinter with reproductive diapause, while the summer-morph adults do not. A low temperature and short photoperiod induce autumn-morph adults. Because of different critical photoperiods between the sexes, the summer-morph males coexist with the autumn-morph adults in late autumn. While autumn-morph males show little mating activity, mating between summer-morph males and autumn-morph females frequently occurs. Thereafter, mated autumn-morph females re-mate with autumn-morph males the following spring. Two hypotheses, a nuptial gift hypothesis and a risk-hedge hypothesis, explaining the adaptive significance of pre-overwinter copulation by autumn-morph females were examined. Wild autumn-morph females were collected in November, late March, April and early May. The decrease in the number of eggs contained in autumn-morph females indicated that they started oviposition in mid-April. The shape of the spermatophore suggested that autumn-morph females could re-mate with autumn-morph males before mid-April. Although the eupyrene sperm of the summer-morph males remained in the spermatheca just after overwintering, the nuptial gift hypothesis is more plausible than the risk-hedge hypothesis because most females re-mated in the spring before the onset of oviposition. A counter-adaptation of summer-morph males acting as a strategy for mating with autumn-morph females was also discussed.