Winter moth (Operophtera brumata) adaptation to climate change: plasticity in embryonic response to temperature

One of the key predictors for larval density in winter moth populations is the amount of synchrony between winter moth egg hatching and host tree bud burst. In four Dutch populations, timing of winter moth egg hatching shows rapid genetic adaptation in response to climate change. Eggs now need higher temperatures to complete development compared to 10 years ago, leading to a better phenological match with timing of their food source, emergence of young oak leaves. The mechanism of how winter moth egg development time responds to temperature remains unclear. To study this, embryonic development was characterized by imagining eggs with epifluorescence microscopy in a split-brood experiment, where eggs were transferred to a warmer or colder temperature compared to baseline at different times during development. Additionally, to identify the genes underlying the response of winter moth egg hatching to temperature, transcriptomes of eggs before and after transfer were sequenced. This study outlines for the first time the different stages of embryonic development in the winter moth, as well as the consequences of temperature in- or decreases on embryonic growth and gene expression at different stages of development. These insights into the mechanism of seasonal timing of egg hatching will help predict future responses of winter moth populations to climate change.