Temperature compensation of circasemilunar timing in the intertidal insectClunio

Abstract

In cultures of a subtropical population of the one-hour midgeClunio tsushimensis, semilunar rhythms of emergence with a period of 15 days can be entrained by using artificial moonlight cycles of 30 days in otherwise invariant 24-h lightdark cycles (0.3 lux over four successive nights every 30 days of LD 12∶12). After changing to an invariant photoperiod (LD 12∶12 without the moonlight programme) or even to continuous darkness, freerunning semilunar rhythms were observed for up to 3 months using cultures of a mixed age structure containing all larval instars. The mean period was 14.2 days at 19 °C, i.e. clearly shorter than under entraining conditions (14.7 days in nature, 15.0 days with the artificial zeitgeber). In the range 14°–24 °C (corresponding to the mean seawater temperatures at the place of origin in winter and summer) there was only slight temperature dependence. The Q10 of the circasemilunar period, however, was not significantly different from 1.0. In continuous darkness the freerunning period was about 15.2 days. Both experiments provide supporting evidence for the existence of a temperature-compensated circasemilunar oscillator acting as an endogenous clock mechanism controlling the timing of imaginal disc formation and pupation in the intertidal chironomid.