Date of Award


Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)



First Advisor

Liam J. Revell

Second Advisor

Ron Etter

Third Advisor

R. Graham Reynolds


Island subpopulations of a widespread species can provide important insights into the process of divergence and diversification. Here, we examined the phylogeography and population structure of the tropical lizard species, Anolis cristatellus, on the Puerto Rican Bank island of Vieques. We first estimated a mitochondrial DNA (mtDNA) gene tree for 379 samples obtained from Vieques Island, the main island of Puerto Rico, and the United States and British Virgin Islands using mitochondrial-gene NADH dehydrogenase 2 (ND2) DNA sequences generated de novo combined with data obtained from GenBank. Subsequently, we genotyped 3,407 single nucleotide polymorphic sites from a subsample of 48 individuals using genotype by sequencing (GBS). First, we found that samples of A. cristatellus from Vieques did not form a monophyletic group in our mtDNA gene tree analysis. Rather, we discovered that samples from Vieques Island belonged to two main subclades: one most closely allied with samples obtained from other Virgin Islands, and the other closely related to samples from the Puerto Rican main island, a pattern that we initially suspected might have been due to the anthropogenic introduction of foreign genetic material from mainland populations to Vieques. Subsequent analysis of our SNP data revealed genetic differentiation across the island of Vieques that is consistent with isolation by distance between the western and eastern ends of the island, but that showed only modest congruence with the aforementioned divergent mtDNA clades. Overall, we conclude that the presence of multiple mtDNA clades on Vieques is natural in origin, not anthropogenic, and suspect that the overall genetic pattern that we have measured across markers likely reflects primary intergradation with a mitochondrial break on the historical Puerto Rican Bank paleo-island (emergent as recently as the Pleistocene) that happens to coincide with the present-day island of Vieques, although we cannot rule out historical allopatry followed by secondary contact.


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