Data from: Temperature has an overriding role compared to photoperiod in regulating the seasonal timing of winter moth egg hatching

To accurately predict species’ phenology under climate change, we need to
gain a detailed mechanistic understanding of how different environmental
cues interact to produce the seasonal timing response. In the winter moth
(Operophtera brumata), seasonal timing of egg hatching is strongly
affected by ambient temperature and has been under strong climate
change-induced selection over the past 25 years. However, it is unclear
whether photoperiod received at the egg stage also influences timing of
egg hatching. Here, we investigated the relative contribution of
photoperiod and temperature in regulating winter moth egg development
using two split-brood experiments. We experimentally shifted the
photoperiod eggs received by 2-4 weeks compared to the actual calendar
date and measured the timing of egg hatching, both at a constant
temperature and in combination with two naturally changing temperature
treatments – mimicking a cold and a warm year. We found an eight-fold
larger effect of temperature compared to photoperiod on egg development
time. Moreover, the very small photoperiod effects we found were
outweighed by both between- and within-clutch variation in egg development
time. Thus, we conclude that photoperiod received at the egg stage does
likely not play a substantial role in regulating the seasonal timing of
egg hatching in the winter moth. These insights into the regulatory
mechanism of seasonal timing could have important implications for
predicting insect climate change adaptation, as we might expect different
targets of selection depending on the relative contribution of different
environmental cues.