Adaptive Differences in Circadian Clock Gene Expression Patterns and Photoperiodic Diapause Induction in<i>Nasonia vitripennis</i>

Abstract

Day length (photoperiod) and temperature oscillate daily and seasonally and are important cues for season-dependent behavior. Larval diapause of the parasitoid <i>Nasonia vitripennis</i> is maternally induced following a certain number of days (switch point) of a given critical photoperiod (CPP). Both the switch point and the CPP follow a latitudinal cline in European <i>N. vitripennis</i> populations. We previously showed that allelic frequencies of the clock gene <i>period</i> correlate with this diapause induction cline. Here we report that circadian expression of four clock genes-<i>period</i> (<i>per</i>), <i>cryptochrome-2</i> (<i>cry-2</i>), <i>clock</i> (<i>clk</i>), and <i>cycle</i> (<i>cyc</i>)-oscillates as a function of photoperiod and latitude of origin in wasps from populations from the extremes of the cline. Expression amplitudes are lower in northern wasps, indicating a weaker, more plastic clock. Northern wasps also have a later onset of activity and longer free-running rhythms under constant conditions. RNA interference of <i>per</i> caused speeding up of the circadian clock, changed the expression of other clock genes, and delayed diapause in both southern and northern wasps. These results point toward adaptive latitudinal clock gene expression differences and to a key role of <i>per</i> in the timing of photoperiodic diapause induction of <i>N. vitripennis</i>.