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)
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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.
KeywordsApyrene sperm Eupyrene sperm Seasonal polyphenism Spermatheca Spermatophore
We thank Dr. T. Yokoi, Assistant Professor, University of Tsukuba, for valuable comments on this research. This work was supported in part by JSPS KAKENHI grant no. 24570019 (MW).
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