Ontogeny shapes vulnerability to climate change underground: Larvae of a subterranean beetle are more sensitive to temperature increase than adults

Although the effects of climate change on biodiversity are increasingly well documented, subterranean ecosystems remain largely understudied. These environments, characterized by stable temperatures and permanent darkness, offer a unique opportunity to assess the vulnerability of low-dispersal species to warming. While recent studies have shown that subterranean invertebrates are highly sensitive to rising temperatures, most research has focused exclusively on adult stages, overlooking the thermal sensitivity of other life stages. Here, we compared the upper thermal limits (LT 50 ) of larvae and adults of Anillochlamys tropica , a cave-dwelling beetle endemic to the southeastern Iberian Peninsula. Individuals were exposed to constant temperatures ranging from 17 °C to 27.5 °C for seven days in controlled laboratory experiments. Adults tolerated temperatures up to 25 °C but died within 24 h at 27.5 °C. In contrast, larvae were significantly more sensitive, showing reduced survival at 23 °C and 25 °C, and exhibiting a lower LT 50 (21.47 ± 0.53 °C) than adults (26.1 ± 0.73 °C). Notably, the current cave temperatures approach the larvae’s thermal limit, meaning that the species could have a narrow thermal safety margin. These findings demonstrate that the early life stages of subterranean beetles are particularly vulnerable to climate warming and underscore the importance of considering all developmental stages when evaluating the impacts of climate change on subterranean biodiversity.