Molecular mechanisms underlying plasticity in a thermally varying environment

Adaptation to environmental variability is a prerequisite for species’ persistence in their natural environments. With climate change predicted to increase the frequency and severity of temperature fluctuations, ectothermic organisms may increasingly depend on acclimation capacity to accommodate thermal variability. To elucidate the molecular basis of fluctuating temperature induced phenotypic plasticity, we investigated heat tolerance and the mechanisms induced by acclimation to thermal variability as compared to those seen at constant temperature. We ran genome-wide transcriptomic analysis on Drosophila melanogaster subjected to acclimation at constant (19 ± 0°C) and fluctuating (19 ± 8°C) temperatures and contrasted the induction of molecular mechanisms in adult males, adult females, and larvae. We found life stage and sex specific dynamics of the acclimation responses to fluctuating temperatures. Adult flies exposed to temperature fluctuations showed a constitutive improvement in heat tolerance while heat tolerance of larvae tracked thermal fluctuations. A constitutive down-regulation of gene expression was observed for several genes in the case of larvae exposed to fluctuations. Our results for adult females showed that, for several genes, fluctuating temperature acclimation resulted in canalization of gene expression. Both transcriptional and post-transcriptional machinery were greatly affected by fluctuations in the case of adult males. Gene ontology analysis showed enrichment of heat stress response involving several major heat shock proteins in both larvae and adults exposed to fluctuating temperatures, even though fluctuations were in a benign range of temperatures. Finally, molecular mechanisms related to environmental sensing seem to be an important component of insect response to thermal variability.

Methods
Phenotypic data from time to knock-down assays performed at different timepoints during larval and adult stage of Drosophila melanogaster. Experimental insects were placed in wells within experimental arenas which were further placed in an incubator set to a high temperature for recording the knock-down time. See the Materials and Methods section of the associated publication for further details.