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

Abstract

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.

VIEWPOINT. Is the Australian subterranean fauna uniquely diverse?

“…data). These findings have been observed in other crustaceans, particularly amphipods and parabathynellids (Cooper et al 2007Guzik et al 2008; K. M. Abrams, unpubl. data).…”

“…Using DNA alone~90 new crustacean 'lineages' were identified from published studies (e.g. up to 21 Pilbara amphipods (Finston and Johnson 2004;Finston et al 2007Finston et al , 2009, 22 Yilgarn amphipods (Cooper et al 2007), 1 anchialine shrimp (Page et al 2008), 24 aquatic isopods ) and 17 parabathynellids (Guzik et al 2008)). Each of these studies also demonstrated geographic isolation for each of the lineages (as above) confirming our species concept using a combined approach as exemplified by Harvey et al (2008) where both morphological and molecular data reinforced conclusions.…”

“…In particular, it was shown in several studies that major geographic barriers inhibit geneflow between regions, i.e. tributaries (Pilbara amphipods Finston and Johnson 2004;Finston et al 2007Finston et al , 2009 or geology of calcrete aquifers (Cooper et al 2007Guzik et al 2008). (3) Genetically divergent lineages were conservatively 16% for pairwise distances based on a Kimura 2-parameter (Kimura 1980) model (i.e.…”

“…While other potentially diverse groups have not been investigated in detail, either because of a lack of attention by existing specialists or a general lack of expertise for specific groups, they are still likely to represent significant diversity. For the 367 undescribed taxa, the majority represent geographically isolated monophyletic lineages, based on molecular studies, reflecting long-term isolated populations that are likely to be equivalent to distinct species, especially for crustaceans, such as parabathynellids (Guzik et al 2008), amphipods (Finston and Johnson 2004;Cooper et al 2007;Finston et al 2007) and isopods . Based on the data presented in Table 1, we predict for the stygofauna that copepods, isopods and beetles are the most poorly known groups, with less than 20% described species, followed by gastropods and amphipods, and for the troglofauna, hexapods (comprising mostly Collembola, Coleoptera, Blattodea and Hemiptera) are the least known relative to the number predicted.…”

Biodiversity, functional roles and ecosystem services of groundwater invertebrates

“…This functional approach to the provision of groundwater ecosystem services complements current studies of stygofaunal systematics and phylogenetics (e.g. Cooper et al 2002Cooper et al , 2007Watts and Humphreys 2006), revealing how groundwater ecosystem services may vary with changes in assemblage composition over time, the likely effects of species loss or invasion, and potential influences of aquifer habitat fragmentation. Such insights can guide protection and restoration of aquifers and their ecosystem services as well as contributing to one of the most exciting fundamental ecological questions of our time.…”