Circadian clock is not ticking in the Antarctic midge, Belgica antarctica

We present the first insights into the molecular mechanism of the circadian clock in a polar insect species, the Antarctic midge (Belgica antarctica). The Antarctic Peninsula, natural habitat of the Antarctic midge, has one of the most dramatic seasonal changes in daylength, ranging from constant light during a summer to extremely short nights in winter. Such light conditions are known to exert a significant impact on the circadian clock in insects living in temperate and tropical zones. Particularly, exposure to constant light causes a temporary shutdown of the circadian clock and subsequent behavioral arrythmicity. Surprisingly, we have shown that the circadian clock of B. antarctica is permanently turned off regardless of external light / dark conditions, in both larvae and adults. The conclusion is based on daily expression profiles of two crucial circadian clock genes period (per) and timeless (tim). Although per and tim genes are expressed in larval and adult heads, they never oscillate in abundance under given photoperiods (constant light or darkness, LD 12h:12h; LD 18:6; LD 6:18) at a constant temperature of 10°C or under field conditions during the Antarctic summer. Additionally, we have demonstrated that locomotor activity is not under circadian control in this species. Larval and adult activity is rather a direct response to changes in light intensity and temperature in field conditions. The Antarctic midge may be the first reported insect species with no apparent circadian clock utilization, which suggests an interesting adaptation for life in a polar region.