Abstract
The life cycle of the birthwort swallowtail butterfly, Atrophaneura alcinous depended on both climatic and biotic factors such as quality of food plant, temperature, photoperiod, starvation and crowding. Not only the induction of diapause, but also the period of diapause depended on photoperiods. The period of diapause depended on various other factors that affected diapause incidence, such as isolation, food quality, temperature and food deprivation. The variability was observed not only among populations but also among individuals within a population, causing the life cycle to split within the population. Three populations of A. alcinous from Kobe (Hyogo Prefecture, Japan) were characterized by the habitat, food plant, behavior, coloration, diapause response, growth rate, body size and temperature tolerance. i.e., woody species vs. weedy species, The data suggests that an open-land population has a simple life cycle, producing more annual generations, whereas a wood-land population is polymorphic, diapausing at different phases of its life cycle. The split life cycle was attributed to adaptation to avoid occasional exhaustion of food plants due to overcrowding caused by the escape from the predation by sequestered toxic substances derived from the host plant. Stable wood-land habitat may favor temporal escape strategy from population catastrophe by diapause, whereas unstable open-land habitat may favor migrant r-strategists to spatially escape such a catastrophe.
