森林に生息する陸生端脚類
1974 年 24 巻 2 号 p. 123-139
詳細
1974 年 24 巻 2 号 p. 123-139
The euterrestrial amphipod population of Orchestia platensis japonica, is intricately constructed of three different phases, viz. (1) age (instar) ; (2) generation ; and (3) subpopulation. The breeding period occurs twice a year, viz. during late May to mid-July and late July to late September. Recruitment during these periods are called the 'spring type' and the 'autumn type', respectively. The life cycle of this population is one year. The spring type produces only the next spring type, while the autumn type exclusively the next autumn type. Individuals of each subpopulation show a sigmoid pattern in their body growth. The animal hatched as spring type overwinters at the 10th or 11th in age, that is just before the adult stage. It becomes an adult next spring and then breeds. On the other hand, the animal recruited as the autumn type overwinters at the 6th or so ages. After wintering the animal begins to grow again and breeds in early autumn. The tendency towards the reproductive separation of the two subpopulations is considered to be a possible prestep to an allochronic speciation.
