Extraordinary micro-endemism in Australian desert spring amphipods.

Increasing pressure for water in the Australian arid zone is placing enormous stress on the diverse endemic communities inhabiting desert springs. Detailed information about the evolutionary processes occurring within and between individual endemic species will help to develop effective and biologically relevant management strategies this fragile ecosystem. To help determine conservation priorities, we documented the genetic structure of the endemic freshwater amphipod populations in springs fed by the Great Artesian Basin in central Australia. Phylogenetic and phylogeographic history and genetic diversity measures were examined using nuclear and mitochondrial DNA from approximately 500 chiltoniid amphipods across an entire group of springs. Pronounced genetic diversity was identified, demonstrating that levels of endemism have been grossly underestimated in these amphipods. Using the GMYC model, 13 genetically divergent lineages were recognized as Evolutionarily Significant Units (ESUs), all of which could be considered as separate species. The results show that due to the highly fragmented ecosystem, these taxa have highly restricted distributions. Many of the identified ESUs are endemic to a very small number of already degraded springs, with the rarest existing in single springs. Despite their extraordinarily small ranges, most ESUs showed relative demographic stability and high levels of genetic diversity, and genetic diversity was not directly linked to habitat extent. The relatively robust genetic health of ESUs does not preclude them from endangerment, as their limited distributions ensure they will be highly vulnerable to future water extraction.