Gene expression responses associated with temperature acclimation in Lasius ants

Climate is one of the most important abiotic variables organisms must adapt to. Ectothermic organisms are particularly dependent on ambient temperature, affecting everything from development to survival. Among these, especially insects are susceptible to desiccation due to their high surface-to-volume ratio. To protect against evaporation, they carry a layer of cuticular hydrocarbons (CHCs) on their cuticle. Their composition is species-specific and can be adjusted to maintain waterproofing during acclimation. However, the molecular mechanisms behind acclimation, and how they vary across species, are still poorly studied. Here we investigated the gene expression response of three congeneric ant species from different habitats acclimated to two constant and one fluctuating temperature regimes. Next to global gene expression and co-expression, we specifically studied the expression of CHC candidate genes. All acclimation treatments resulted in a small number of differentially expressed genes (DEGs), with the fluctuating regime showing the fewest. This suggests that fluctuating temperatures may mitigate the potentially stressful effects of constant temperatures. Lasius brunneus displayed the weakest acclimation response in terms of gene expression and was also the most strongly affected by desiccation. This suggests low plasticity, and thus potentially a higher vulnerability to climate change. Co-expression network analysis revealed that CHC candidate genes were distributed randomly across co-expression modules in all species. Additionally, module preservation analyses indicated highly similar global gene co-expression patterns across all three species, despite their distinct ecological niches. Our findings highlight the importance of studying gene expression alongside other (or higher-level) phenotypic traits to understand the mechanisms underlying phenotypic plasticity. Furthermore, they suggest that some species may be more susceptible to climate change than others due to limited acclimation capacity.