Trans-biome diversity in Australian grass-specialist lizards (Diplodactylidae: Strophurus)

Abstract

Comparisons of biodiversity patterns within lineages that occur across major climate gradients and biomes, can provide insights into the relative roles that lineage history, landscape and climatic variation, and environmental change have played in shaping regional biotas. In Australia, while there has been extensive research into the origins and patterns of diversity in the Australian Arid Zone (AAZ), how diversity is distributed across this biome and the Australian Monsoonal Tropics (AMT) to the north, has been less studied. We compared the timing and patterns of diversification across this broad aridity gradient in a clade of lizards (Strophurus: phasmid geckos) that only occur in association with a unique Australian radiation of sclerophyllous grasses (Triodia: spinifex). Our results indicate that overall genetic diversity is much higher, older and more finely geographically structured within the AMT, including distantly related clades endemic to the sandstone escarpments of the Kimberley and Arnhem Plateau. Niche modelling analyses also suggest that the distribution of taxa in the AMT is more strongly correlated with variation in topographic relief than in the AAZ. The two broad patterns that we recovered - (i) lineage endemism increases as latitude decreases, and (ii) endemism is tightly correlated to rocky regions - parallel and corroborate other recent studies of habitat generalists and specialised saxicoline lineages occurring across these same regions. Early Miocene diversification estimates also suggest that, soon after Triodia grasses colonised Australia and began to diversify in the Miocene, phasmid geckos with Gondwanan ancestry shifted into these grasses, and have subsequently remained closely associated with this unique vegetation type.

Origins and patterns of endemic diversity in two specialized lizard lineages from the Australian Monsoonal Tropics (Oedura spp.)

“…In this study, we inferred initial diversification of two focal clades of Oedura from the Kimberley around the Miocene–Pliocene boundary. Similar crown ages have been inferred for many other radiations centred on the AMT (Catullo & Keogh, ; Laver, Nielsen, Rosauer, & Oliver, ; Oliver, Doughty, & Palmer, ; Toon et al., ). Furthermore, while some endemic AMT radiations may be younger (e.g.…”

Crypsis and convergence: integrative taxonomic revision of the Gehyra australis group (Squamata: Gekkonidae) from northern Australia

“…The wide distribution of this form across the southern portions of the AMT broadly overlaps with the northern deserts region (sensu Cracraft, 1991; but see González-Orozco et al, 2014). This distribution also mirrors that of several other species and lineages that have likewise only been identified recently, supporting the hypothesis that the southern AMT has a distinct associated endemic biota (Smith et al, 2011;Catullo et al, 2014;Laver et al, 2017). Referred material.…”

“…The SNP data provided a crucial test for the lack of gene flow between closely related taxa in areas of geographic contact or even overlap. Many analyses of mtDNA diversity in other Australian lizard species have revealed similarly deep genetic divergences (Oliver, Doughty & Palmer, 2012;Laver et al, 2017;, but corroborating independent evidence for evolutionary distinctiveness and the absence of contemporary of gene flow has been lacking. Where geographic sampling is sufficiently extensive, SNP data offer the potential to provide for direct tests of lack of recent genetic introgression between such problematic populations (Singhal et al, 2018).…”

“…Etymology. The species epithet is formed from the Latin words calcis (limestone) and tectus (hidden, hideaway), as in 'limestone-hidden' or 'limestone hideaway', in reference to the few loci, have revealed deep and geographically fine-grained phylogeographic structure (Oliver, Doughty & Palmer, 2012;Moritz et al, 2016Moritz et al, , 2018Potter et al, 2016;Laver et al, 2017;. With a few exceptions (Doughty, Ellis & Oliver, 2016;Afonso Silva et al, 2017;Moritz et al, 2018), the taxonomic status of much of this diversity remains to be evaluated.…”

Initial Expansion of C4 Vegetation in Australia During the Late Pliocene

“…In this interpretation, the intensification of the EAWM ( Figure S4 in the supporting information), itself thought to be related to ongoing late Cenozoic global cooling (Herbert et al, 2016;Ge et al, 2013;Lu et al, 2010;Raymo, 1994), for the first time pushed the Intertropical Convergence Zone far enough southward to develop a substantial summer monsoon in northern Australia, characterized by a strong seasonal precipitation contrast and potentially greater incidence of fire. The relatively late appearance of a distinctly monsoonal moisture regime in northern Australia may help to explain the Plio-Pleistocene evolution of animal clades confined to the Australian monsoon tropics today that are nested within lineages more typical of inland, arid Australia (Laver et al, 2017;Nielsen et al, 2016). The establishment of this new climatic regime would have provided the ecological opportunities necessary for the expansion of C 4 vegetation in Australia beginning at~3.5 Ma.…”