Evolutionary responses of energy metabolism, development, and reproduction to artificial selection for increasing heat tolerance in Drosophila subobscura

Adaptation to warming conditions involves increased heat tolerance and
metabolic changes to reduce maintenance costs and maximize biological
functions close to fitness. Evidence shows that energy metabolism evolves
in response to warming conditions, but we know little about how heat
stress intensity determines the evolutionary responses of metabolism and
life history traits. Here, we evaluated the evolutionary responses of
energy metabolism and life-history traits to artificial selection for
increasing heat tolerance in Drosophila subobscura, using two protocols to
measure and select heat tolerance: slow and fast ramping protocols. We
found that the increase in heat tolerance was associated with reduced
activity of the enzymes involved in the glucose-6-phosphate branchpoint,
but no changes in the metabolic rate in selected lines. We also found that
the evolution of increased heat tolerance increased the early fecundity in
selected lines and increased the egg-to-adult viability only in the
slow-ramping selected lines. This work shows heat tolerance can evolve
under different thermal scenarios but with different evolutionary outcomes
on associated traits depending on the heat stress intensity. Therefore,
spatial and temporal variability of thermal stress intensity should be
taken into account to understand and predict the adaptive response to
ongoing and future climatic conditions.