Amidst the current climate emergency, scientists are renewing their efforts to accurately predict and anticipate the impact of climate change on biodiversity. To comply with this grand challenge, several global syntheses and strategic action plans have delineated biodiversity and climate change targets. Unfortunately, the subterranean environment- likely, the most widespread non-marine environment on Earth- has been systematically neglected in these global strategies. Subterranean ecosystems are some of the most understudied ecosystems on Earth and only recently we began to grasp their eco-evolutionary importance and economic value. So, what impediments prevent the establishment of effective protection of subterranean biota and their inclusion in global conservation goals? the lack a mechanistic understanding of subterranean species response to global change seems to have stalled most attempts so far. With this project, we take advantage of the unique natural laboratory offered by caves for ecological research to establish direct links between species' physiology and vulnerability to climate change. One of the main limitations of mechanistic approaches to predict species vulnerability to climate change is that obtaining physiological information for species is costly, and thus the main insights provided in this fields are derived from a reduced set of species. Recently, we have demonstrated that the specialization process to live in deep subterranean habitats involves a reduction of upper lethal limits, but not an adjustment to habitat temperature in a clade of subterranean beetles from the Pyrenees. Thus, as the selective pressures during the process to specialization to live in deep subterranean environments appear to have generated convergent syndromes spanning both morphological and physiological traits, we firstly expect to be able to predict the heat tolerance values for the complete clade (ca. 160 species) just using morphological traits as predictive variables (much easier to obtain than physiological data). However, predictions of species vulnerability to climate change based on physiological data could be refined at a deeper level by considering other factors that affect species thermal tolerance (i.e., plasticity (acclimation capability) of heat tolerance and a decrease in relative humidity). Within the theoretical framework of the climactic variability hypotheses we expect that the decrease in heat tolerance caused by desiccation stress will be higher for highly specialized species, exposed to lower climatic variability, and also that these species have lost (or reduced) the ability to acclimate to different ambient temperatures. Finally, combining all this information we aim to assess the
capability of different species and populations to face climate change, providing the most accurate prediction of species response to climate change so far for a complete clade of subterranean species. Thus, contrary to the general theory that high altitude species will be at higher extinction risk under future climatic conditions, we could demonstrate that highly specialized subterranean species living in the warmer areas will be the most vulnerable to an increase in temperature. The results of this project will provide important insights to develop the field of conservation physiology for subterranean biodiversity.