Geographical Range and Circadian Rhythms

Abstract

WHILE studying the effect of different photoperiods on the circadian rhythm of flight activity in the mosquito Aedes aegypti (L.), I observed that within a certain range of photoperiods the phase-setting effects of light-on (“dawn”) and light-off (“dusk”) reinforce each other; the range over which this reinforcement occurs coincides with that of the photoperiod which is usually encountered by this species throughout its natural geographical range¹. If these two phenomena are associated in Ae. aegypti, one would expect the association also to hold in other species. I have recently carried out tests on various species of mosquito, deriving theoretical geographical ranges from their circadian rhythms and comparing these with the actual known ranges. The fit was very close in almost every case.