Latitudinal variation in circadian rhythmicity in Nasonia vitripennis

Many physiological processes of living organism show circadian rhythms governed by an endogenous clock. This clock has a genetic basis and is entrained by external cues such as light and temperature. Other physiological processes exhibit seasonal rhythms, that are also responsive to light and temperature. We previously reported a natural latitudinal cline of photoperiodic diapause induction in the parasitic wasp Nasonia vitripennis in Europe and a correlated haplotype frequency for the circadian clock gene period (per). To evaluate if this correlation is reflected in circadian behaviour, we investigated circadian locomotor activity of seven populations from the cline. We found that the proportion of rhythmic males is higher than females in constant darkness, and that mating decreased rhythmicity of both sexes. Only for virgin females tau increased weakly with latitude. Wasps from the most southern locality had an overall lower level of circadian locomotor activity and an onset, peak and offset of activity earlier during the 24 h period, than wasps from the most northern locality. We evaluate this variation in rhythmicity as a function of period haplotype frequencies in the populations and discuss its functional significance in the context of local adaptation.