Friday, December 9, 2016

The Frilled Lizard and its phylogeography

A typical defensive display of a Frilled Lizard.
The savanna-dwelling Australo-Papuan Frilled Lizards' spectacular threat display has made the lizard world famous. They are distributed across northern Australia and southern New Guinea. In a recent  Molecular Phylogenetics and Evolution article Pepper and colleagues (2017) examine the Frilled Lizard's phylogeography as it relates to changes in the savanna vegetation in the Plio/Pleistocene and the associated increase in aridity. The authors generated sequence data for one mitochondrial and four nuclear DNA loci (5052 base pairs) for 83 frilled lizards sampled throughout their range. They also quantified body proportion variation for 279 individuals. Phylogenetic analyses based on maximum likelihood and Bayesian species-tree methods resulted in three shallow clades that replace each other across the monsoon tropics. They found the expected pattern of male biased sexual size dimorphism in both maximum body size and head size but there was no sexual dimorphism in overall body shape or in frill size, relative to head size, supporting the hypothesis that the frill is used primarily as a threat display rather than a sexual display. The genetic clades are broadly consistent with known clinal variation in frill color that gradually shifts from west to east (red, orange, yellow/white) but otherwise show little morphological differentiation in body proportion measures. The biogeographic breaks between clades occur at the Carpentaria Gap and the lowlands surrounding the Ord River. Ecological niche modeling predicts where habitat suitability for Frilled Lizards in these regions. Extremely low intra-clade genetic diversity over vast geographic areas is indicative of recent gene flow that would likely have been facilitated by widespread savanna during interglacials, Or alternatively, may reflect population bottlenecks induced by extreme aridity during Pleistocene glacials. The shallow divergence between Australian and New Guinean samples is consistent with recent connections between Australia and New Guinea that would have been  via a savanna corridor across the Torres Strait. The authors do not support taxonomic recognition of any of the frilled lizard clades and consider C. kingii a single species with shallow phylogeographic structure and clinal variation in frill color.

Pepper M, Hamilton DG, Merkling T, Svedin N, Cser B, Catullo RA, Pryke SR, Keogh JS. Phylogeographic structure across one of the largest intact tropical savannahs: Molecular and morphological analysis of Australia’s iconic frilled lizard Chlamydosaurus kingii. 2017. Molecular Phylogenetics and Evolution. 106:217-27.

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