How ants acclimate: Impact of climatic conditions on the cuticular hydrocarbon profile

1. Organisms from temperate zones are exposed to seasonal changes and must be able to cope with a wide range of climatic conditions. Especially ectotherms, including insects, are at risk to desiccate under dry and warm conditions, the more so given the changing climate. 2. To adjust to current conditions, organisms acclimate through changes in physiology, morphology and/or behaviour. Insects protect themselves against desiccation through a layer of cuticular hydrocarbons (CHC) on their body surface. Hence, acclimation may also affect the CHC profile, changing their waterproofing capacity under different climatic conditions. 3. Here, we investigated the acclimation response of two Temnothorax ant species to different climatic conditions. We analysed CHC profiles of queens, nurses and foragers that were acclimated to different humidityxtemperature regimes, and tested the beneficial acclimation hypothesis by measuring survival of workers under desiccation-heat stress. Both ants possessed a species-specific CHC profile. Nevertheless, they showed similar acclimation responses concerning changes of certain CHC classes, and finally similar survival rates under desiccation-heat stress. Warm-acclimated individuals generally showed longer n-alkanes, fewer dimethyl alkanes, and more (workers) or less (queens) monomethyl alkanes. In contrast, dry conditions resulted in more n-alkanes and fewer mono- and dimethyl alkanes, but these acclimatory changes were only observed in workers and not in queens. Warm- and dry-acclimated workers survived desiccation-heat stress better, but we found no species differences. 4. Our results indicate that both ant species can plastically adjust their cuticular hydrocarbon profile, allowing them to acclimate to different climatic conditions. Although their CHC composition differs in a species-specific manner, they showed similar chemical adjustments and concomitant changes in survival rate. Hence, chemical plasticity may be critical to determine a species' climatic range and its survival under changing climatic conditions.