Geographical variation in egg diapause in Sympetrum frequens

摘要

The effects of photoperiod and temperature on the termination of egg diapause were examined in Sympetrum frequens. Eggs were obtained from adult females collected from three locations in Japan and incubated under short- or long-day photoperiods at a constant temperature of 25, 20, or 15°C. Egg diapause was eventually terminated in all treatments. Because differences in the average developmental time were small among the temperature treatments, it was concluded that the rate of diapause development is more rapid at lower temperatures, as in other Odonata species. A clear geographic trend was not found in the egg period, which may reflect the life cycle of S. frequens: the timing of reproduction is the same or even earlier in higher than in lower latitudes. Relatively large variations in embryonic period were found among populations and even within a population at 15°C, suggesting that the rate of diapause development is also variable. The results also suggested that a short photoperiod might prevent S. frequens eggs from hatching before the onset of winter.