Genetic Basis Underlying Rapid Evolution of an Introduced InsectOphraella communa(Coleoptera: Chrysomelidae): Heritability of Photoperiodic Response

The introduced beetle Ophraella communa LeSage has adapted to local environments in Japan in a short period by adjusting the photoperiodic response for induction of reproductive diapause. Based on these results, we predicted that the O. communa population has significant genetic variation in this trait on which natural selection should act. To examine the type and amount of genetic variation in photoperiodic response in O. communa, we performed artificial selection on this trait in opposite directions, i.e., directions of diapausing and nondiapausing under a photoperiod of 13:11 (L:D) h, using three Tsukuba (Japan) lines derived from different years (2005, 2006, and 2012). Bidirectional selection shifted the diapause incidence to 100% in six or seven generations (diapausing selection) or 0% in five to eight generations (nondiapausing selection). The offspring produced by hybridization between diapausing and nondiapausing lines exhibited a wide range of diapause incidence under a photoperiod of 13:11 (L:D) h, depending on the differences in the number of selected generations between the two parental lines. These results show that the photoperiodic response of O. communa is not inherited in a simple Mendelian manner but under polygenic control. Based on the results of artificial selection, we estimated the heritability of photoperiodic response, assuming polygenic inheritance. The heritability estimates were 0.770 to 0.856 in diapausing lines and 0.208 to 0.620 in nondiapausing lines, indicating substantial genetic variation in this trait. Thus, genetic variation in photoperiodic response of O. communa is one factor allowing the beetle to adapt rapidly to newly colonized habitats.