Assessing the vulnerability of subterranean biodiversity to climate change from an experimental perspective

Research into the impacts of climate change on subterranean biodiversity has made significant progress in recent years, revealing profound effects occurring at gene to community levels, with varying strength and direction. However, our knowledge of how subterranean organisms, often constrained by a reduced capacity for dispersal or microhabitat selection, cope with environmental variation is still very limited. In this context, basic aspects of their thermal biology remain largely unexplored, such as their capacity to adjust thermal tolerance through physiological plasticity and evolutionary change, or the factors that affect such thermal tolerance and hence, their sensitivity to climate change. Experimental approaches exploring relevant physiological traits for coping with environmental stress are essential for providing insights into these questions. Indeed, subterranean ecosystems ideally exemplify how experimental data can provide more realistic predictions of species responses to climate change than traditional approaches based on correlative species distribution models.

I will give an overview of recent advances in climate change research on subterranean fauna based on such an experimental perspective. I will especially focus on the work conducted by my research group using mainly insects as study models. Our early studies revealed that specialization to the climatically stable deep subterranean environment involved a reduction of the physiological capacity and plasticity to withstand thermal variability. Surprisingly, a wide gap between upper thermal limits and mean habitat temperature has been found across different and disparate arthropod groups, suggesting a lack of adjustment of heat tolerance to current local temperature in subterranean ectotherms. These findings point to a key role of thermal variability in shaping thermal tolerance, apparently irrespective of mean temperature. Prediction exercises of species responses to climate change that account for experimentally measured thermal tolerance draw a different and less dramatic fate for subterranean species than those based only on projected changes in habitat availability modeled from distribution data. I will discuss future perspectives on how such predictions might be further refined by different complementary approaches. For example, exploring thermally sensitive processes at the molecular level to identify early signs of sublethal stress, as well as accounting for other limiting factors for subterranean species, which may potentially interact with temperature, could provide a more ecologically relevant approach to organismal physiological tolerance. Our ongoing research is also directed towards estimating rates of evolutionary change from experimentally measured thermal tolerance traits to predict the margin for evolutionary rescue of subterranean species under a rapidly changing climate.

Despite the technical obstacles that experimental work entails in these habitats, the subterranean environment provides unique opportunities for advancing the field of conservation physiology. Integrating physiological knowledge into vulnerability assessments should be a priority to design informed conservation strategies that effectively protect subterranean biodiversity amidst the challenges posed by global change.