Temperature compensation of circasemilunar timing in the intertidal insectClunio

Summary

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.