Ecophysiological consequences of variability in diapause intensity

Diapause intensity (DI) is a physiological trait represented by the duration of diapause under given conditions of environment. In many species, it is highly variable, probably being controlled by multiple genes and tends to form a cline in response to the latitudinal gradient of selection pressure. DI clines could be established artificially by crossing between lines of a cricket selected for different levels of DI, indicating the importance of genetic factors in the adaptive variation of DI. However, DI may be modified in response to seasonal cues both before and after the onset of diapause. Polymorphism in the intensity of prolonged diapause may split adults of a single population to emerge in different years. A unimodal distribution of DI may also result in polymodal termination of diapause, if DI variation is so large that chilling in one winter is not enough to terminate diapause for all members of a population. Bimodal termination of diapause after overwintering suggests heterogeneity in the final phase of diapause that requires high temperatures in spring. Polymodal termination of diapause subserves a bet-hedging strategy. Variability in DI thus provides insects with an important means of adaptation to their environments changing in space and time