Conservation of subterranean biodiversity in Western Australia: using molecular genetics to define spatial and temporal relationships in two species of cave-dwelling Amphipoda

Abstract

The Jewel Cave karst system in southwestern Australia contains a community of aquatic invertebrates that is listed as critically endangered owing to lowering water levels in cave lakes. A key question for conservation of biodiversity patterns was to determine the most appropriate spatial scale; viz. lake microscale, cave mesoscale, catchment macroscale, or regional megascale). A second key question was to understand the historical relationship between the community and cave water levels, necessary to evaluate the risk of extinction related to predictions of drying climate in southwestern Australia. This study used molecular genetic techniques (allozyme electrophoresis and mitochondrial DNA sequencing) to assess spatial and temporal relationships in two species of crangonyctoid amphipods (Uroctena sp. and Perthia cf. acutitelson Straškraba) from the Jewel Cave system and other karst drainage systems, springs and surface waters in the Leeuwin-Naturaliste karst region. The molecular data indicated the existence of two cryptic species within Perthia cf. acutitelson. Within the Jewel Cave karst system, populations sampled from separate groundwater pools both within and between caves were largely panmictic, with no evidence of population sub-structuring in Uroctena sp. and only a subtle suggestion of heterogeneity in Perthia sp. 1. Beyond the Jewel Cave system, populations of Perthia sp. 1 occurring in separate karst drainage systems and surface catchments are strongly differentiated at the population genetic level. For conservation of biodiversity patterns in Perthia sp. 1 and Uroctena sp., the most appropriate spatial scale is the macrohabitat represented by the karst aquifer or hydrogeologic system. The minimum age estimates, based on molecular clock methods, for divergence of the cave populations from nearby surface populations are > 250 ka. The molecular data support the likelihood that the amphipods in Jewel Cave survived in situ lower watertable levels experienced 11 to 13 ka, that coincided with the phase of regional aridity in southwestern Australia near the end of the Pleistocene. However, if the present trend of declining rainfall in southwestern Australia continues, and if water levels in the Jewel Cave system decline below 22.7 m above sea level (ASL), then most of the lakes will become dry and the aquatic invertebrate community will be more vulnerable to extinction because of reduced habitat and consequent reduced population size.