Independent Transitions between Monsoonal and Arid Biomes Revealed by Systematic Revison of a Complex of Australian Geckos (<i>Diplodactylus</i>; Diplodactylidae)

<div><p>How the widespread expansion and intensification of aridity through the Neogene has shaped the Austral biota is a major question in Antipodean biogeography. Lineages distributed across wide aridity gradients provide opportunities to examine the timing, frequency, and direction of transitions between arid and mesic regions. Here, we use molecular genetics and morphological data to investigate the systematics and biogeography of a nominal Australian gecko species (<i>Diplodactylus conspicillatus sensu lato</i>) with a wide distribution spanning most of the Australian Arid Zone (AAZ) and Monsoonal Tropics (AMT). Our data support a minimum of seven genetically distinct and morphologically diagnosable taxa; we thus redefine the type species, ressurrect three names from synonymy, and describe three new species. Our inferred phylogeny suggests the history and diversification of lineages in the AAZ and AMT are intimately linked, with evidence of multiple independent interchanges since the late Miocene. However, despite this shared history, related lineages in these two regions also show evidence of broadly contrasting intra-regional responses to aridification; vicarance and speciation in older and increasingly attenuated mesic regions, versus a more dynamic history including independent colonisations and recent range expansions in the younger AAZ.</p></div

Holotype of <i>D</i>. <i>barraganae</i> sp. nov. (NTM R21395).

<p>Musselbrook Reserve, Border Waterhole, Northern Territory/Queensland border. (Image: Jeff Wright).</p

Variation in snout colouration and scalation.

<p>(A) Canthal stripe present (<i>D</i>. <i>conspicillatus</i> SAMA R32133); (B) Canthal stripe absent or very weakly developed (<i>D</i>. <i>platyurus</i> AMS R158426). Condition A applies to all members of the <i>D</i>. <i>conpicillatus</i> group except <i>D</i>. <i>platyurus</i>. (C) 1^st supralabial (1) greatly enlarged and contacting nasal scale (N) (<i>D</i>. <i>conspicillatus</i> SAMA R42589); (D) 1^st supralabial (1) not enlarged and widely separated from ventral edge of nasal scale (N) (<i>D</i>. <i>platyurus</i> AMS R 158426). Condition C is found in all members of the <i>D</i>. <i>conspicillatus</i> group except <i>D</i>. <i>platyurus</i>. Note in images C & D that R = rostral scale (Images: A & B Jeff Wright, QM; C & D Geoff Thompson, QM).</p

Lectotype of <i>Gymnodactylus laevis</i> (SMF8242).

<p>Hermannsburg Mission, Northern Territory. (Image: Dr Hal Cogger). This specimen was removed from the gut of a <i>Varanus gouldii</i> and is partially digested and in poor condition.</p

Summary of key meristic and mensural data for species in the <i>D</i>.<i>conspicillatus</i> complex.

<p>Summary of key meristic and mensural data for species in the <i>D</i>.<i>conspicillatus</i> complex.</p

Distribution of species in the <i>Diplodactylus conspicillatus</i> complex based on morphological analyses of holdings in Australian museums.

<p>Pink = <i>D</i>. <i>custos</i><b>sp. nov</b>., Blue = <i>D</i>. <i>hillii</i>, Green = <i>D</i>. <i>barraganae</i><b>sp. nov</b>., Purple = <i>D</i>. <i>platyurus</i>, Red = <i>D</i>. <i>conspicillatus</i>, White = <i>D</i>. <i>laevis</i>, Yellow = <i>D</i>. <i>bilybara</i><b>sp. nov</b>. Dashed lines indicate approximate locations of biogeographic breaks mentioned in the text.</p

Museum Voucher and locality details of all specimens included in phylogenetic analyses.

<p>Museum Voucher and locality details of all specimens included in phylogenetic analyses.</p

Holotype of <i>D</i>. <i>hillii</i> (QMJ 1994).

<p>Port Darwin, Northern Territory (Image—Jeff Wright, QM).</p

Holotype of <i>Diplodactylus bilybara</i> sp. nov. (WAM R174500).

<p>21km south of Barradale, Western Australia. (Image: Peter Waddington, QM).</p

Distribution of genetically sampled individuals for major genetic lineages in the <i>D</i>. <i>conspicillatus</i> complex.

<p>Pink = <i>D</i>. <i>custos</i><b>sp. nov</b>., Blue = <i>D</i>. <i>hillii</i>, Green = <i>D</i>. <i>barraganae</i><b>sp. nov</b>., Purple = <i>D</i>. <i>platyurus</i> (circle = lineage F, star = lineage G, squares = lineage H), Red = <i>D</i>. <i>conspicillatus</i> (squares = northern lineage, circles = southern lineage), White = <i>D</i>. <i>laevis</i>, Yellow = <i>D</i>. <i>bilybara</i><b>sp. nov</b>. The dashed line corresponds to the transition between regions with a moisture index (mean annual rainfall divided by evaporation) less than 0.4 (arid) to greater than 0.4 (semiarid to mesic) and is widely used as an approximate boundary of the Australian Arid Zone. Inset map on the top left corner indicates putative regions of endemism mentioned in the text; P = Pilbara, K = Kimberley, TE = “Top End”, G = Gulf country.</p