Evolution and Latitudinal Variation in Life Cycles of Oak Macrolepidopterans

Combining two life history characteristics, the overwintering and the larval growing periods, the life cycles of oak Macrolepidopterans in four different climatic zones were classified into nine types and five subtypes. The frequency of the spring-growing types increases and that of the summer-growing types decreases northward. The summer-growing types are considered to be more adaptive to the long growth season at lower latitudes, while the spring-growing types to the short growth season at higher latitudes. From this geographic pattern, the life cycle evolution in oak Macrolepidopterans is inferred as follows. Probably, the ancestral species had a nondiapause asynchronous life cycle in the tropics. With expansion of the distribution range to the subtropical and temperate zones, synchronous life cycles with diapause would have evolved as adaptation to the seasonal conditions. In the course of this evolution, diapause in each of the five developmental stages (egg, larva, prepupa, pupa and adult) would have originated independently of one another. With further expansion northward, life cycles of the spring-growing type adaptive to the cool temperate and boreal zones would have evolved from life cycles of the summer-growing types adaptive to the subtropics and the warm temperate zone.