Effects of photoperiod and aging on the adult spermatogenesis of Polygonia c-aureum (Lepidoptera: Nymphalidae), in relation to adult diapause
Adult spermatogenesis of Polygonia c-aureum was compared between non-diapausing and diapausing butterflies before overwintering. This butterfly has seasonal polyphenism, i.e., summer and autumnal forms. Summer form butterflies that emerged in summer reproduce shortly after emergence, while autumnal forms that emerged in autumn mate in spring. Immatures were reared under either a long photoperiod, which produced the summer form without diapause or under a short photoperiod, which produced the autumnal form with diapause. We found almost no differences in adult spermatogenesis between the two seasonal forms, indicating that adult spermatogenesis is not related to adult diapause. Although adult diapause in the autumnal form is maintained under short photoperiods and terminated under long photoperiods, such a photoperiod did not affect the spermatogenesis of the autumnal form. Our earlier studies indicate that relatively few eupyrene and apyrene sperm are produced after overwintering. Although apyrene spermatogenesis occurred in young adults, eupyrene spermatogenesis did in a small scale before overwintering. These results suggest strongly that male autumnal form butterflies prepare the sperm until overwintering, which had been formed during the larval, pupal and young adult stages.