Abstract
Understanding how natural selection acts on the genome and contributes to the process of speciation is a primary aim of the study of evolution. Here we used natural variation in two subspecies of the Guadeloupean anole (Anolis marmoratus ssp.), from the island of Guadeloupe in the Lesser Antilles, to explore the genomic basis of adaptation and speciation in Anolis lizards. These subspecies inhabit distinct ecological environments and display marked differences in adult male color and pattern. We sequenced the complete genomes of 20 anoles, 10 from each subspecies, at 1.4× coverage. We used genome-wide scans of population differentiation, allele frequency spectrum, and linkage disequilibrium to characterize the genomic architecture within and between the subspecies. While most of the genome was undifferentiated, we observed five large divergent regions. Within these regions we identified blocks, 5 kb pairs in length, enriched for fixed single nucleotide polymorphisms. These blocks encompass 97 genes, two of which are candidate pigmentation genes. One is melanophilin (mlph), which helps transport melanosomes within melanocytes. The other is a cluster of differentiation 36 (cd36), which regulates carotenoid pigment sequestration. We used high-pressure liquid chromatography to confirm that carotenoid pigments are significantly more abundant in the conspicuous orange-pigmented skin of male A. m. marmoratus suggesting that cd36 may be regulating pigment deposition in this tissue. We identified for the first time a carotenoid gene that is a potential target of divergent sexual selection and may be contributing to the early stages of speciation in Anolis lizards.