Timing of increased temperature sensitivity coincides with nervous system development in winter moth embryos

Climate change is rapidly altering the environment and many species will
need to genetically adapt their seasonal timing to keep up with these
changes. Insect development rate is largely influenced by temperature, but
we know little about the mechanisms underlying temperature sensitivity of
development. Here we investigate seasonal timing of egg hatching in the
winter moth, one of the few species which has been found to genetically
adapt to climate change, likely through selection on temperature
sensitivity of egg development rate. To study when during development
winter moth embryos are most sensitive to changes in ambient temperature,
we gave eggs an increase or decrease in temperature at different moments
during their development. We measured their developmental progression and
timing of egg hatching, and used fluorescence microscopy to construct a
timeline of embryonic development for the winter moth. We found that egg
development rate responded more strongly to temperature once embryos were
in the fully extended germband stage. This is the phylotypic stage at
which all insect embryos have developed a rudimentary nervous system.
Furthermore, at this stage timing of ecdysone signaling determines
developmental progression, which could act as an environment dependent
gateway. Intriguingly, this may suggest that, from the phylotypic stage
onward, insect embryos can start to integrate internal and environmental
stimuli to actively regulate important developmental processes. As we
found evidence that there is genetic variation for temperature sensitivity
of egg development rate in our study population, such regulation could be
a target of selection imposed by climate change.