日本産オオミズアオ属(ヤママユガ科)の地理的変異と亜種間交雑

In this paper, the subspecific characteristics of the eggs, larvae and adults of lunar moths, Actias gnoma (BUTLER) and A. artemis(BREMER et GREY), are described. Results of inter-subspecific crossing of the moths and discussion on the zoogeography of the two species are also given. 1. In adults, A. gnoma mandschurica from Hokkaido and A. gnoma gnoma from Honshu are similar but A. gnoma miyatai from the Izu islands is definitely different from them. The latter has smaller body and fore-wing with small eye-spot and soft curved apex than the former two. The adults of two subspecies of A. artemis, A. a. artemis from Hokkaido and A. a. aliena from Honshu, show no detectable differences in the morphological characters. The male of subsp. artemis has blue wings instead of yellow ones found in A. a. aliena. While, the non-diapausing pupae of A. a. artemis, reared at high temperature (25℃) and long-day conditions, yield yellowish males which are similar to the summer form of subsp. aliena. 2. There are obvious differences in the coloration among the 1st inster larvae of Actias subspecies. The head, prothoracic shield, setae and body surface are black in A. gnoma mandschurica and A. artemis artemis from Hokkaido blackish-brown in A. gnoma gnoma, yellowish-brown in A. artemis aliena from Honshu and pale reddish-yellow (Hachijo-jima) or reddish-brown (Kozu-shima and Miyake-jima) in A. gnoma miyatai from the Izu Islands. The variation of the larval coloration can be regard as adaptation to temperature in their habitats. 3. The male genitalic structure of A. g. miyatai is different from the other subspecies. In the former, the uncus has dorsal lamellar plates which are laid to overlap each other and incurved, while in the latter two, uncus has broad lamellar ones which are recurved. The length of the juxta in subsp. miyatai is shorter than in subsp. gnoma and the processes from juxta in the former are nearly symmetrical but those of the latter are asymmetrical, that is, the right process is longer than the left. The symmetrical juxta of the former may be considered more primitive than the latter, because asymmetrical ones are found related species, A. selene and A. neidhoeferi. 4. Hybrids of crossing among these subspecies showed the intermediate characters of their parents in the first (F_1) and the second (F_2) generations. 5. The difference of geographical distribution of the two species may have been due not only to differences of their food plants but also to difference of their invasion periods into Japanese Islands in Old ages (perhaps in cold climate Pleistocene). A. artemis is general feeder of broad-leaved deciduous trees. On the other hand, A. gnoma is oligophagous on alders (Alnus species). As was pointed out by PEIGLER (1986), A. gnoma would have changed it's food plant into alders in the glacial period. Perhaps, a factor preventing immigration of A. gnoma to Kyushu might have been effuse distribution of the food plant. 6. The allopatric distribution of two ssp. of A. gnoma, A. g. miyatai from Kozu-shima to Aoga-shima Islands and A. g. gnoma from Honshu to Izu-o-shima Islands, is particularly interesting. This phenomenon seems to be the result of difference of historical ages of the invasions of the two subspecies. It seems that A. g. miyatai did not specialize in the Izu Islands but arose in somewhere in the Continent Asia. After the settlement of miyatai, the Izu Islands were isolated and the new dominant subspecies, gnoma, could invaded only Izu-o-shima which is volcanic and the closest to Honshu.