Facing lethal temperatures: heat shock response in desert and temperate ants

Several genera of desert ants have adapted to endure prolonged exposure to high temperatures. The study of these ants is thus essential to unravel how species respond and adapt to thermal stress. We investigated the thermal tolerance and the transcriptomic heat stress response of three desert ant genera adapted to withstand high temperatures (Cataglyphis, Melophorus and Ocymyrmex) and two temperate genera (Formica and Myrmica) to explore convergent and specific adaptations. We found a variable transcriptomic response among desert species exposed to similar levels of physiological heat-stress: Cataglyphis holgerseni and Melophorus bagoti differentially regulated very few transcripts (54 and 53, respectively), while Cataglyphis bombycina and Ocymyrmex robustior showed greater expression alterations (affecting 253 and 698 transcripts, respectively). These two responsive mechanisms of lower and higher gene expression changes were related to desert species thermal tolerance survival pattern and convergently evolved in distinct desert ant genera. Moreover, the two temperate species tested differentially expressed thousands of genes more than desert ants in response to heat stress, suggesting that keeping restrained gene expression is an important adaptation in heat adapted species. Finally, we found a significant overlap of the molecular pathways activated in response to heat-stress in temperate and desert species. This indicates that the molecular processes involved in heat-stress survival appears to be evolutionary conserved in ants, even though taxonomically restricted genes also participated in the heat stress response.