The Dynamics of Natural Selection and Vicariance in the Dominican Anole: Patterns of Within-Island Molecular and Morphological Divergence

Abstract

Abstract. The larger islands of the Lesser Antilles are ecologically and geologically complex and are inhabited by single, but morphologically variable, Anolis species. Although earlier work has indicated that a large part of the morphological variation in Anolis oculatus from Dominica can be attributed to selection, a history of recurrent volcanic activity over the last few million years suggests that vicariance may have also played a significant role. We report a study of variation in the cytochrome b gene of mitochondrial DNA across the island to address this issue. We uncovered a very high degree of polymorphism, with an overall gene diversity of 0.97 and a nucleotide diversity of 0.04. Sequences, on average, differ by 3.82% and the maximum pairwise divergence (corrected for multiple hits) is 9.29%. Most haplotypes are restricted to single localities (a pattern not changed by increasing the sample size). Phylogenetic analysis revealed the presence of two distinct lineages on the island with strong phylogeographic structure. One of these is geographically restricted to a relatively small part of the central Caribbean coast. Sublineages were also discernible within the other more widely distributed lineage, but resolution within and support for these sublineages was poor. The phylogeographic pattern is not congruent with generalized body shape and scalation, but is significantly correlated with color pattern. Even when correcting for this lineage effect with partial Matrix correspondence tests, the relationship between color pattern and vegetation is reaffirmed, suggesting that although both vicariance and selection have played a role in the morphological differentiation of this species, selection for current environmental conditions has been more important. We discuss the causes of the phylogeographic structure in light of the volcanic history of the island and highlight the exceptional instance of congruence between all morphological character systems and lineage boundaries, which occurs at the transition between the northern and southern Caribbean ecotypes.

The relative importance of ecology and geographic isolation for speciation in anoles

“…Hence, while populations on small islands may often be thought of as fragile, it appears that anole populations may be very large and robust on small islands. This is compatible with the observations that currently no island or habitable islet in the Lesser Antilles is without anoles, and they may withstand even cataclysmic volcanic activity (Malhotra & Thorpe 2000). Consequently, this suggests that anole populations may increase rapidly in size after the founding colonization, and that, while bottlenecks may occur, they are not particularly vulnerable to prolonged bottlenecks after establishment.…”

Early stages of divergence: phylogeography, climate modeling, and morphological differentiation in the South American lizard Liolaemus petrophilus (Squamata: Liolaemidae)

“…Because a fossil calibration for L. petrophilus is currently lacking, we calibrated the tree by fitting a lognormal distribution around a sequence divergence rate of 1.6% per million years with a standard deviation of 0.12, and a relaxed uncorrelated lognormal clock model (see Results). The distribution of mutation rates encompassed the three substitution rates used in previous studies of Liolaemus (Morando et al 2003) and is derived from previous studies using cytochrome b from other squamate reptiles (Giannasi 1997; Zamudio and Greene 1997; Malhotra and Thorpe 2000). Because we were working with intraspecific data, we used a constant size tree prior, as this model is more appropriate for these type of data (Ho 2007).…”

Replicated ecological landscapes and the evolution of morphological diversity amongGasterosteuspopulations from an archipelago on the west coast of Canada

“…One of the dominant themes to emerge in such investigations is the primacy of selection in structuring morphological and behavioural adaptations among taxa (Reimchen 1994;Baldwin 1997;Grant 1998;Losos et al 1998;Malhotra and Thorpe 2000;Grant and Grant 2002).…”