Monday, November 30, 2015

[Herpetology • 2016] Mitochondrial Introgression via Ancient Hybridization, and Systematics of the Australian Endemic Pygopodid Gecko genus Delma

Fig. 3. Geographic distributions and interspecific relationships within major species groups:
(A) Delma australis group and D. concinna, image of Delma hebesa from Fitzgerald River National Park, WA;
(B) ‘inornate’ group, and image of Delma nasuta from Pannawonica, WA;
(C) D. mitella, and morphologically similar D. fraseri and D. plebeia groups, image of Delma fraseri from Kalbarri, WA;
(D) northwestern Australia group and D. labialis, image of Delma borea from El Questro Station, WA.
 (E) shows extent of the Australian arid zone in grey, and proposed Miocene shrubland corridors adapted from Cracraft (1986), with image of potential vegetative corridor, Acacia and Eucalyptus canopy with tussock grass and shrubby understory from near Kellerberrin, WA. All photos courtesy of Ryan Ellis.

• Molecular phylogenetic methods identify four major species groups within Delma.
• Multiple instances of hybridization belie previous phylogenetic assessment.
• Most species lineages are young, diverging <10 MYA, during Miocene aridification.
• Further work towards understanding species boundaries in Delma is necessary.

Of the more than 1500 species of geckos found across six continents, few remain as unfamiliar as the pygopodids – Family Pygopodidae (Gray, 1845). These gekkotans are limited to Australia (44 species) and New Guinea (2 species), but have diverged extensively into the most ecologically diverse limbless radiation save Serpentes. Current phylogenetic understanding of the family has relied almost exclusively on two works, which have produced and synthesized an immense amount of morphological, geographical, and molecular data. However, current interspecific relationships within the largest genus Delma Gray 1831 are based chiefly upon data from two mitochondrial loci (16s, ND2). Here, we reevaluate the interspecific relationships within the genus Delma using two mitochondrial and four nuclear loci (RAG1, MXRA5, MOS, DYNLL1), and identify points of strong conflict between nuclear and mitochondrial genomic data. We address mito-nuclear discordance, and remedy this conflict by recognizing several points of mitochondrial introgression as the result of ancient hybridization events. Owing to the legacy value and intraspecific informativeness, we suggest the continued use of ND2 as a phylogenetic marker. Results identify strong support for species groups, but relationships among these clades, and the placement of several enigmatic taxa remain uncertain. We suggest a more careful review of Delma australis and the ‘northwest Australia’ clade. Accurately assessing and addressing species richness and relationships within this endemic Australian Gekkotan genus is relevant for understanding patterns of squamate speciation across the region.

Keywords: Mitochondrial capture; Introgression; Biogeography; Pygopodidae; Gekkota

Ian G. Brennan, Aaron M. Bauer and Todd R. Jackman. 2016. Mitochondrial Introgression via Ancient Hybridization, and Systematics of the Australian Endemic Pygopodid Gecko genus Delma.  Molecular Phylogenetics and Evolution. 94, Part B; 577–590. DOI: 10.1016/j.ympev.2015.10.005