産卵期におけるモリアオガエルの生態について : 第2報 産卵時の行動・その他

抄録

The green frog, Rhacophorus schlegelii var. arborea OKADA et KAWANO has a peculier breeding habit, i.e., a female deposits the eggs on leaves of trees and grasses near ponds with special assistance of three of four males. The coupling occurs usually at night or at day-break and the coupled frogs begin to walk to and fro, but are seldom found in the day time. Just after or before the onset of the oviposition, the males found near the path of this pair come together one by one to make a ovipositing group. In many cases they occupy the position on the dorsal or lateral side of the other early joined male as is shown on the left of Fig.3,but sometimes a certain male in the ovipositing group does not take the position on the upside of the early joined male but holds to the small twigs of trees near the ovipositing place (right of Fig.3). Regarding the sizes of the males in ovipositing group, two cases are distinguished. The one in which the sizes are larger in the more early participated male than in the latter one (Table 1,type II), in a ward these accord with their participation order. The sizes in the other case are not in accord (types III and IV). Near the end of oviposition, the males begin to leave the egg mass ; in type II this retreat takes palce inversely to the participation order, but in types III or IV it is independent of this order. However, in both cases the largest male among the ovipositing group remains until the end of oviposition. Hence, the writer is inclined to consider that the body size of the male and its position in the group are involved in its duration joining in the egg oviposition. The eggs are laid with gelatinous substance, which is beat up by the rotatory movement of the hind legs of the males and the female, into a foamy mass. Between the rotatory movement and the next movement the frogs take breath, this breathing time shows the prolonging tendency with the progress of the oviposition. The movement of the male takes place together with that of the female, regardless of their participation order and body size (Fig. 5). Further it was confirmed by microscopical examination that all males in the ovipositing group participated in fertilizing the eggs. It was observed that some males joined again in the ovipositing group. Consequently, at least, that the sex-ratio observed at the time of oviposition became 1 : 3-4 seems not to mean the actual ratio in number of each sex. However it seems that the sex-ratio of this variety is about 1 : 1 when the other facts are considered.