Distinct Physiological Mechanisms Induce Latitudinal and Sexual Differences in the Photoperiodic Induction of Diapause in a Fly

Abstract

Many temperate insects enter diapause (dormancy) for overwintering in response to short days (long nights). A latitudinal cline in the critical day lengths for the photoperiodic induction of diapause has been reported in a variety of insect species. However, the physiological mechanisms underlying this cline have remained elusive. We approached this issue in the flesh fly Sarcophaga similis, in which the photoperiodic time measurement system meets the 'external coincidence model'. In this model, measuring day lengths depends on whether the photoinducible phase (φi), determined by a circadian clock, is exposed to light or not. First, we detected a clear latitudinal cline in the critical day lengths of flies collected from four localities at different latitudes. The phase positions of the φi, which can be verified by night interruption photoperiods, also showed a clear latitudinal cline. This result supports the hypothesis that the latitudinal cline in the critical day lengths is produced by the difference in the phase positions of the φi among different strains. A sexual difference in the critical day lengths for photoperiodic induction has also been detected in various species. In this study, a sexual difference in the critical day lengths was observed in the southern strains, but p. 3 there was no sexual difference in the phase positions of the φi. This result indicates that both sexes measure photoperiods in the same manner. Males are less sensitive than females to the light pulse given at the φi, suggesting a quantitative difference in the photoperiodic time measurement and counter systems. This study clearly reveals that distinct mechanisms induce latitudinal and sexual differences in the critical day lengths for the photoperiodic induction of diapause in a fly.

Latitudinal clines in the timing and temperature‐sensitivity of photoperiodic reproductive diapause in Drosophila montana

“…Latitudinal variation in CDL represents an adaptation to early and rapid arrival of winter at higher latitudes, and small changes in photoperiod on either side of the CDL produce a dramatic shift in diapause incidence (Bale and Hayward 2010). Accordingly, most studied insect species have been found to show latitudinal variation in this trait (Bradshaw and Lounibos 1977, Lankinen 1986, Kimura and Bessho 1993, Shimizu and Kawasaki 2001, Tyukmaeva et al 2011, Wang et al 2012, Lankinen et al 2013, Paolucci et al 2013, Lehmann et al 2015, Yamaguchi and Goto 2019. In addition, rapid changes in CDL have been detected in several invasive species after colonization (Gomi et al 2007, Bean et al 2012, Urbanski et al 2012, Tanaka et al 2015 or as a response to climate warming (Bradshaw andHolzapfel 2001, Dalin 2011).…”

Clock-talk: have we forgotten about geographic variation?

“…2) Pterostichus nigrita 2p,2° 24, 120, 8 Gulf Cos Thiele ( 1977 , Fig. 1A) Sarcophaga similis 4p,11° 24, 120, 12 Mid (15) Yamaguchi and Goto ( 2019 , Figs. 4,5) Tetranycus urticae 1p 24, 60, 10 Gulf & NC Cos (10) Vaz Nunes and Veerman ( 1984 , Fig.…”

“…The substance accumulates in the counter system. When the level of the accumulated substance exceeds a certain ‘internal threshold,’ diapause induction is determined, whereas nondiapause development is determined when the accumulation is lower than the threshold…” (Yamaguchi and Goto 2019 , pp. 294 & 296).…”

Urban warming and artificial light alter dormancy in the flesh fly

“…By contrast, males are more likely to enter diapause, as late-emerging males are penalized in terms of fewer mating opportunities [ 60 ]. Female features that tend to avert diapause [ 50 , 61 ] imply that urban environments affect each sex differently. This hypothesis should be tested in a future study.…”