Abstract
Desert mound springs of the Great Artesian Basin in central Australia maintain an endemic fauna that have historically been considered ubiquitous throughout all of the springs. Recent studies, however, have shown that several endemic invertebrate species are genetically highly structured and contain previously unrecognised species, suggesting that individuals may be geographically ‘stranded in desert islands’. Here we further tested the generality of this hypothesis by conducting genetic analyses of the obligate aquatic phreatoicid isopod Phreatomerus latipes. Phylogenetic and phylogeographic relationships amongst P. latipes individuals were examined using a multilocus approach comprising allozymes and mtDNA sequence data. From the Lake Eyre region in South Australia we collected data for 476 individuals from 69 springs for the mtDNA gene COI; in addition, allozyme electrophoresis was conducted on 331 individuals from 19 sites for 25 putative loci. Phylogenetic and population genetic analyses showed three major clades in both allozyme and mtDNA data, with a further nine mtDNA sub-clades, largely supported by the allozymes. Generally, each of these sub-clades was concordant with a traditional geographic grouping known as spring complexes. We observed a coalescent time between ∼2–15 million years ago for haplotypes within each of the nine mtDNA sub-clades, whilst an older total time to coalescence (>15 mya) was observed for the three major clades. Overall we observed that multiple layers of phylogeographic history are exemplified by Phreatomerus, suggesting that major climate events and their impact on the landscape have shaped the observed high levels of diversity and endemism. Our results show that this genus reflects a diverse fauna that existed during the early Miocene and appears to have been regionally restricted. Subsequent aridification events have led to substantial contraction of the original habitat, possibly over repeated Pleistocene ice age cycles, with P. latipes populations becoming restricted in the distribution to desert springs.
Highlights
Australia’s arid zone, as defined by Byrne et al 2008 [1], comprises one of the largest desert regions in the world
Phylogenetic Analyses Based on MtDNA Overall 597 bp of the mtDNA gene COI were sequenced for 476 individuals from a total of 69 springs from southern Lake Eyre, South Australia (Table S1)
The phylogenetic analysis of COI haplotypes among P. latipes of the mound springs revealed three primary clades, hereafter referred to by their rough geographic position relative to Lake Eyre: C (Central), S (Southern) and N (Northern) (Fig. 2)
Summary
Australia’s arid zone, as defined by Byrne et al 2008 [1], comprises one of the largest desert regions in the world. Despite its low average rainfall of 100–250 mm per year, this region harbours a multitude of diverse and endemic faunal groups, such as lizards [2], birds [3], ants [4], and even aquatic animals [5,6] The origins of this biome date back to the late Tertiary, since central Australia was considered ‘‘warm and wet’’ until the Miocene [1,7]. The immensity and complexity of Australia’s arid region means that additional phylogeographic studies are required for other taxa that have survived aridification before we can fully understand the impact of aridity and the nature of the environment that preceded it Reflecting this need, extant taxa found in relictual, aquatic, arid-land ecosystems are ideally suited for this purpose, since they have survived despite enduring arguably the most dramatic climate shifts experienced by any of the desert faunas [16]
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