Abstract
The green anole (Anolis carolinensis) has been widely used as an animal model in physiology and neurobiology but has recently emerged as an important genomic model. The recent sequencing of its genome has shed new light on the evolution of vertebrate genomes and on the process that govern species diversification. Surprisingly, the patterns of genetic diversity within natural populations of this widespread and abundant North American lizard remain relatively unknown. In the present study, we use 10 novel nuclear DNA sequence loci (N = 62 to 152) and one mitochondrial locus (N = 226) to delimit green anole populations and infer their historical demography. We uncovered four evolutionarily distinct and geographically restricted lineages of green anoles using phylogenetics, Bayesian clustering, and genetic distance methods. Molecular dating indicates that these lineages last shared a common ancestor ∼2 million years ago. Summary statistics and analysis of the frequency distributions of DNA polymorphisms strongly suggest range-wide expansions in population size. Using Bayesian Skyline Plots, we inferred the timing of population size expansions, which differ across lineages, and found evidence for a relatively recent and rapid westward expansion of green anoles across the Gulf Coastal Plain during the mid-Pleistocene. One surprising result is that the distribution of genetic diversity is not consistent with a latitudinal shift caused by climatic oscillations as is observed for many co-distributed taxa. This suggests that the most recent Pleistocene glacial cycles had a limited impact on the geographic distribution of the green anole at the northern limits of its range.
Highlights
Anolis carolinensis, or the green anole lizard, is the first lepidosaurian reptile to have its entire genome sequenced [1]
Intronic sequences ranged in length from 688 bp to 1288 bp and anonymous loci ranged from 211 bp to 557 bp
How Many Populations? The mtDNA phylogeny and STRUCTURAMA analysis both indicate that there are at least four distinct green anole populations. We identify these populations as (1) the Everglades in southern FL, (2) the Suwannee on the Gulf coast of FL, (3) the Gulf-Atlantic and (4) the North Carolina (NC) clade (Carolinas for nDNA)
Summary
The green anole lizard, is the first lepidosaurian reptile to have its entire genome sequenced [1]. The sequence of events during the evolution of vertebrate axial skeleton segmentation as revealed by the Anolis genome [3] suggests that cyclically expressed patterns in the ‘‘segmentation clock’’ have not necessarily undergone a stepwise pattern from fish to mammals. The relative paucity of isochores in the Anolis genome [4] suggests that variation in GC composition is less integral to genomic structure than previously thought. In addition to these recent contributions to the field of comparative genomics, anoles as a group have been the focus of investigators in ecology and evolution for decades. The Anolis genome will shed light on the genetic basis of morphological and ecological adaptation but the process of speciation itself [6]
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