Size and shape assortative mating in Japanese beetles (Popilliajaponica)

Abstract

Assortative mating is hypothesized to be a product of sexual selection, mating constraints, or temporal autocorrelation. I test these hypotheses in the Japanese beetle (Popillia japonica Newman, 1841), a sexually size dimorphic invasive insect pest in North America, by measuring the size and shape of bodies and wings of pair members in a wild population. Because male P. japonica prefer to mate with larger females and larger males outcompete rivals for mating opportunities, sexual selection is expected to produce size-related assortative mating. The current study did not support this hypothesis. The mating constraints hypothesis was also not supported because beetle pairs did not have similar body shapes. I, however, did find support for the temporal autocorrelation hypothesis as the wing size and shape of pair members were significantly correlated. This mating pattern likely arises due to individuals with larger and more slender wings arriving earlier at aggregation sites and pairing according to their arrival sequence. Although I found less support for the sexual selection hypothesis, I argue that mate choice might play an important, but secondary, role to temporal autocorrelation in explaining assortative mating in Japanese beetles.