The circadian clock gene (Clock) regulates photoperiodic time measurement and its downstream process determining maternal induction of embryonic diapause in a cricket

response, occurs in advance of diapause, the most extreme example of which is when this sensitive stage occurs in one generation and diapause in the next (i.e. a maternal effect) (Mousseau & Dingle, 1991).The circadian clock that regulates the rhythm of locomotor activity comprises at least a dozen circadian clock genes, including period (per), timeless (tim), mammaliantype cryptochrome (cry-m or cry2), cycle (cyc), Clock (Clk), Par domain protein 1 (Pdp1), vrille and clockwork orange (Tomioka, 2014;Tomioka & Matsumoto, 2015;Patke et al., 2020).The principal mechanism associated with these genes is a transcription-translation feedback loop, which takes approximately 24 h to complete.Involvement of the circadian clock in photoperiodic time measurement was fi rst proposed by Erwin Bünning in the 1930s (Bünning, 1936), and subsequently, further models were proposed, initially a modifi ed version of Bünning's original model, referred to as the 'external coincidence model', and thereafter an alternative hypothesis, the 'internal coincidenceThe circadian clock gene (Clock) regulates photoperiodic time measurement and its downstream process determining maternal induction of embryonic diapause in a cricket *