Adaptive significance of the recurrent photoperiodic response in a spring-breeding carabid beetle, Carabus yaconinus

Abstract

Seasonal changes in the photoperiodic sensitivity for reproduction in adults of a spring-breeding carabid beetle, Carabus yaconinus (Coleoptera: Carabidae), were examined by transferring adults from outdoor to photoperiodic conditions in various seasons. Newly-emerged adults transferred to the laboratory in September to December showed a long-day photoperiodic response, but lost photoperiodic sensitivity gradually during winter. In late April, overwintered adults were not sensitive to the photoperiod, with females continuing to have mature eggs under both long-day and short-day conditions. In contrast, in late June and late July, the adults were sensitive to the photoperiod, with only those kept under short-day conditions re-entering reproductive diapause. This recovery of photoperiodic sensitivity appears to play a definitive role in maintenance of diapause in autumn for adults that have reproduced. The adults collected in late April regained photoperiodic sensitivity in two months even after being kept under unchanged conditions. Therefore, no environmental cue is required for recovery of photoperiodic sensitivity, which apparently recovers with the lapse of time. Our results suggest that the recurrent photoperiodic response is required in long-living adults of C. yaconinus to regulate the timing of reproduction, and also indicate a difference in photoperiodic sensitivity in summer between overwintered and newly-emerged adults.