Some like it hot: physiological responses of hot-rod ants (Hymenoptera: Formicidae) and their interactions with past and future climate change

Small organisms tend to lose water more rapidly than larger ones because of their high surface area relative to their body volume. In hot arid regions, desiccation resistance is an important trait for these organisms as they are exposed to high day temperatures and scarcity of water. For instance, Ocymyrmex ants have evolved physiological adaptations that enable them to survive the dry environments in which they live. These ants are adapted to forage at ground temperatures exceeding 50 °C. In this study, we investigated the physiological traits that enhance thermo-tolerance across selected Ocymyrmex species, collected from different climatic zones in South Africa. We measured and compared desiccation resistance, critical thermal limits, and cuticular hydrocarbon composition of these ants and tested whether these traits are evolutionary conserved or labile. We also investigated whether these adaptations are maintained by evolutionary constraints or environmental factors. Our results demonstrated that these ants have high thermal limits, are resistant to desiccation, and that their cuticular hydrocarbons are composed of long chains dominated by linear alkanes, which are believed to be beneficial for waterproofing. The results also showed a strong phylogenetic signal for desiccation tolerance, which could indicate that desiccation tolerance is an ancestral trait in this group of ants. In contrast, there was weak evidence for phylogenetic signal in critical thermal limits across all species, which could indicate that these traits are ubiquitous rather than varying across species from different environments.