Subterranean archipelago in the Australian arid zone: mitochondrial DNA phylogeography of amphipods from central Western Australia.

In 1998, a unique subterranean ecosystem was discovered in numerous isolated calcrete (carbonate) aquifers in the arid Yilgarn region of Western Australia. Previous morphological and genetic analyses of a subterranean water beetle fauna suggest that calcrete aquifers are equivalent to closed island habitats that have been isolated for millions of years. We tested this hypothesis further by phylogeographic analyses of subterranean amphipods (Crangonyctoidea: Paramelitidae and Hyalidae) using mitochondrial DNA sequence data derived from the cytochrome oxidase I gene. Phylogenetic analyses and population genetic analyses (samova) provided strong evidence for the existence of at least 16 crangonyctoid and six hyalid divergent mitochondrial lineages, each restricted in their distribution to a single calcrete aquifer, in support of the 'subterranean island (archipelago) hypothesis' and extending its scope to include entirely water respiring invertebrates. Sequence divergence estimates between proximate calcrete populations suggest that calcretes have been isolated at least since the Pliocene, coinciding with a major aridity phase that led to the intermittent drying of surface water. The distribution of calcretes along palaeodrainage channels and on either side of drainage divides, have had less influence on the overall phylogeographic structure of populations, with evidence that ancestral crangonyctoid and hyalid species moved between catchments multiple times prior to their isolation within calcretes. At least two potential modes of evolution may account for the diversity of subterranean amphipod populations: dispersal/vicariance of stygobitic species or colonization of calcretes by surface species and independent evolution of stygobitic characteristics.

Cooper SJ ，Bradbury JH ，Saint KM ，Leys R ，Austin AD ，Humphreys WF ... -  《MOLECULAR ECOLOGY》

Cryptic speciation in two widespread subterranean amphipod genera reflects historical drainage patterns in an ancient landscape.

The landscape of the Pilbara region of Western Australia has been relatively unchanged for 100 million years. The ancient river systems of this region might be expected to be sources of isolation and divergence for aquatic species. Hence, the occurrence of widespread groundwater taxa in this landscape offers the opportunity to examine associations between genetic diversity and drainage patterns. Pilbarus and Chydaekata are two widespread genera of subterranean amphipods endemic to the Pilbara, each occupying multiple tributaries. We used molecular data to examine the roles of drainage patterns in structuring genetic diversity. Gene flow within a tributary may be facilitated by the occasional occurrence of these amphipods in springs, which results in their downstream dispersal during episodic flooding. However, tributary boundaries may form hydrological barriers to gene flow, resulting in localised isolation of populations and divergence. Samples of both genera, collected throughout three river basins, were examined for sequence divergence in the cytochrome c oxidase I mitochondrial gene. There was no evidence of contemporary gene flow among populations of either genus, and each tributary contained highly divergent lineages, which were not associated with similar morphological differentiation. This suggests cryptic speciation has occurred, and similar phylogenetic signals in both taxa imply similar evolutionary histories. Surface populations may have been driven into subterranean refugia by the cessation of flow in the rivers, associated with Tertiary climate change, while morphological evolution may have been constrained by stabilising selection. The lack of congruence between molecular diversity and morphology raises important practical issues for conservation.

Finston TL ，Johnson MS ，Humphreys WF ，Eberhard SM ，Halse SA ... -  《MOLECULAR ECOLOGY》

Fine-scale comparative phylogeography of a sympatric sister species triplet of subterranean diving beetles from a single calcrete aquifer in Western Australia.

Calcrete aquifers in the arid Yilgarn region of central Western Australia are a biodiversity hotspot for stygofauna. A distinct pattern of interspecific size class variation among subterranean dytiscid beetle species has been observed in 29 of these aquifers where either two or three small, medium and/or large sympatric species are found that are in some cases sister species. We used a 3.5 km(2) grid of bores to sample dytiscids on a fine-scale and employed a comparative phylogeographical and population genetic approach to investigate the origins of a sympatric sister species triplet of diving beetles from a single aquifer. Mitochondrial DNA sequence data from the Cytochrome oxidase c subunit I gene revealed that all three species have high levels of haplotype diversity with ancient (approximately 1 million years ago) intra-specific coalescence of haplotypes, but low levels of nucleotide diversity. Population analyses provide evidence for multiple expansion events within each species. There was spatial heterogeneity in the distribution of genetic variation and abundance both within and among the three taxa. Population analyses revealed significant fine-scale differentiation with isolation by distance for Paroster macrosturtensis and P. mesosturtensis, but not the smallest species P. microsturtensis. Haplotype network analyses provided limited or no evidence for past population fragmentation within the large and small species, but substantial historical divergence was observed in P. mesosturtensis that was not spatially structured. A patchy population structure with contemporaneous and historical isolation by distance in the three species is likely to have been a significant isolating and diversifying force, preventing us from ruling out a potential role for allopatric divergence during speciation of this beetle sister triplet.

Guzik MT ，Cooper SJ ，Humphreys WF ，Austin AD ... -  《-》

Biogeography of the stygobitic isopod Pygolabis (Malacostraca: Tainisopidae) in the Pilbara, Western Australia: evidence for multiple colonisations of the groundwater.

Finston TL ，Francis CJ ，Johnson MS 《-》

Independent colonization and extensive cryptic speciation of freshwater amphipods in the isolated groundwater springs of Australia's Great Artesian Basin.

Murphy NP ，Adams M ，Austin AD 《-》