Phylogeny, ecology, and the nature of cladogenesis in Australian pygopopid lizards
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All five groups of lizards in Australia underwent adaptive radiations within this continent. Most investigations into this phenomenon have taken place from the community ecology level. Evolutionary perspectives, on the other hand, have lagged behind, because of the lack of phylogenetic hypotheses for these groups. In this study, I chose the lizard family Pygopodidae as a model group from which to examine this problem. Pygopodids are a group of limb-reduced and elongate lizards consisting of 36 extant species that are endemic to Australia and New Guinea. In Chapter 1, I examine the systematics of pygopodids. Analyses of morphological, mtDNA, and nDNA data using parsimony, maximum likelihood, and Bayesian methods yielded trees with similar ingroup topologies. However, rooting trees with the two outgroup taxa (Diplodactylus spp.) led to much uncertainty about the true location of the root, owing to probable long-branch attraction problems. To resolve this rooting issue, I rooted molecular trees using a molecular clock. I resolved intergeneric relationships by evaluating several hypotheses via the method of parametric bootstrapping. A revised phylogenetic hypothesis for pygopodids emerged from these analyses, and a new species of Delma is described. In Chapter 2, I analyzed body size and tail proportion variation among pygopodids. Pygopodids show strong positive ontogenetic allometry of tail length. This pattern was also found among species, but a size-independent increase in tail size was observed for the Delma clade, compared to its sister clade. Analysis of body size evolution in the group suggests that ancestral pygopodids were large-bodied, which according to allometric trends observed among extant species, suggests that these ancestral lizards also had relatively long tails. This finding therefore suggests the mechanism by which pygopodids underwent the transition from a gecko-like animal to a snake-like animal, namely they may have evolved into diurnal grass or shrub-dwelling specialists. In Chapter 3, I analyzed cladogenetic patterns in the group. Analysis of lineage-through time plots, which were calibrated with an early Miocene pygopodid fossil, and biogeographic patterns, suggest that most extant pygopodid species have originated since the early Miocene, a finding that is consistent with the hypothesis that climate change, particularly aridification, may have played a role in Australian lizard diversifications.