Where Angels Fear to Tread: Developments in Cave Ecology

Heat tolerance and acclimation capacity in subterranean arthropods living under common and stable thermal conditions

Cave-dwelling ectotherms, which have evolved for millions of years under stable thermal conditions, could be expected to have adjusted their physiological limits to the narrow range of temperatures they experience and to be highly vulnerable to global warming. However, most of the few existing studies on thermal tolerance in subterranean invertebrates highlight that despite the fact that they show lower heat tolerance than most surface-dwelling species, their upper thermal limits are generally not adjusted to ambient temperature. The question remains to what extent this pattern is common across subterranean invertebrates. We studied basal heat tolerance and its plasticity in four species of distant arthropod groups (Coleoptera, Diplopoda, and Collembola) with different evolutionary histories but under similar selection pressures, as they have been exposed to the same constant environmental conditions for a long time. Adults were exposed at different temperatures for 1 week to determine upper lethal temperatures. Then, individuals from previous sublethal treatments were transferred to a higher temperature to determine acclimation capacity. Upper lethal temperatures of three of the studied species were similar to those reported for other subterranean species (between 20 and 25°C) and widely exceeded the cave temperature (13-14°C). The diplopod species showed the highest long-term heat tolerance detected so far for a troglobiont (i.e., obligate subterranean) species (median lethal temperature after 7 days exposure: 28°C) and a positive acclimation response. Our results agree with previous studies showing that heat tolerance in subterranean species is not determined by environmental conditions. Thus, subterranean species, even those living under similar climatic conditions, might be differently affected by global warming.

Shedding light on the hidden world of subterranean fauna: A transdisciplinary research approach

Subterranean environments contain a diverse and unique obligate fauna: either aquatic living in the groundwater or terrestrial living in voids above the water table. In the arid region of the western part of the Australian continent, a particularly rich subterranean fauna coincides with a concentration of natural resource extraction operations. Since the inclusion of subterranean fauna in assessments of environmental impact in the mid-1990s, taxonomic research in Australia on this group of mainly invertebrates has grown exponentially. However, remaining knowledge gaps continue to frustrate both environmental regulators and development proponents due to high uncertainty in the decision-making process. In early 2017, the Western Australian Biodiversity Science Institute was tasked with leading the development of a research program to improve on the current state of knowledge of subterranean fauna. To balance the diverse environmental, economic and social needs of a range of stakeholders, transdisciplinary principles were applied to program development. A clear consensus on five broad focus areas to progress include: (1) data consolidation; (2) resilience to disturbance; (3) survey and sampling protocols; (4) abiotic and biotic habitat requirements; and (5) species delineation. In the context of these focus areas; we describe the research program development, reviewing the status of knowledge within each focus area, and the research initiatives to close the gaps in knowledge. We argue that, by adopting a transdisciplinary approach, the likelihood of success of the research program, as measured by the effective translation and adoption of research findings, will be maximized. This review is timely given the ever-increasing demand on groundwater systems for water extraction worldwide. A holistic understanding of the influence of anthropogenic activities on these ecosystems, and the functional role of organisms within them, will help to ensure that their health is not compromised.