“Adaptive differences in circadian clock gene expression patterns and photoperiodic diapause induction in Nasonia vitripennis”
Elena Dalla Benetta, Leo W. Beukeboom, and Louis van de Zande (June 2019)
Knock down of the clock gene period changes the pace and the phase of the circadian clock and delays diapause response
Adaptive differences in circadian clock gene expression patterns and photoperiodic diapause induction in Nasonia vitripennis
In 2017, the Nobel prize in medicine was awarded for the discovery of the endogenous circadian clock, that enables organisms from bacteria to plants and animals to exhibit biological rhythms adapted to daily (circadian) and annual environmental oscillations. Studies on the genetics of the clock have revealed much complexity and variation. The Marie Skłodowska-Curie Initial Training Network (ITN) INsecTIME was initiated to train early scientists to investigate the (neuro)genetics that underlie biological timing. Here we report variation in circadian clock gene expression patterns in the parasitoid wasp Nasonia vitripennis. This wasp has a photoperiodically induced larval dormancy state called diapause When adult females experience certain critically short daylight conditions, which is dependent on geographical location, they produce diapausing larvae that resume development when conditions are favorable. The study reveals that geographical differences in circadian clock gene regulation under different photoperiods may play a role in regulating this seasonal adaptation. In particular the expression of the clock gene period is important for setting the pace and the phase of Nasonia daily rhythms as well as in the timer mechanism responsible for diapause induction. This shows that genes of the circadian clock are involved in seasonal timing as well, and therefore links the evolution of circadian and circannual adaptive mechanisms.
Day length (photoperiod) and temperature oscillate daily and seasonally and are important cues for season-dependent behavior. Larval diapause of the parasitoid Nasonia vitripennis is maternally induced following a certain number of days (switch point) of a given critical photoperiod (CPP). Both the switch point and CPP follow a latitudinal cline in European N. vitripennis populations. We previously showed that allelic frequencies of the clock gene period correlate with this diapause induction cline. Here, we report that circadian expression of four clock genes, period (per), cryptochrome-2 (cry-2), clock (clk) and cycle (cyc), 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 in constant conditions. Per RNAi 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 towards adaptive latitudinal clock-gene expression differences and to a key role of per in the timing of photoperiodic diapause induction of N. vitripennis.