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

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.

Are Partial Mantel Tests Adequate?

“…One may also want to assess the relative importance of environmental factors (e.g., temperature, depth of a river, or altitude) or migration flow on an observed response matrix or vector (e.g., the genetic distance matrix between pairs of samples or the species abundance vector). In this peculiar case, the test generally used is the partial Mantel test (Smouse et al 1986;Leduc et al 1992; Thorpe et al 1994;Malhotra and Thorpe 2000). We demonstrate here that the partial Mantel test is not generally valid and discuss possible alternatives.…”

Contrasting Patterns of Floral and Molecular Variation Across a Cline in Mimulus Aurantiacus

“…This way, the association between flower color and geography could be assessed after accounting for the effect of neutral genetic differentiation and vice versa. If a significant association persists between Q ST and geographic distance after we control for the effects of neutral genetic divergence, we can reject the hypothesis that neutral processes are sufficient to explain the presence of the morphological cline (Malhotra and Thorpe 2000;Storz 2002). …”

“…Conversely, genetic distance has only negligible power to predict phenotypic divergence after controlling for the effects of geographic distance. Therefore, phenotypic differences in flower color across the cline are much greater than a purely neutral model could account for, indicating that current or recent selection is responsible for maintaining floral variation (see also Thorpe et al 1996;Malhotra and Thorpe 2000;Storz 2002). The weak evidence for neutral divergence among the races also argues against the possibility of recent secondary contact after a long period of allopatry.…”

Parallel Evolution and Vicariance in the Guppy (Poecilia Reticulata) Over Multiple Spatial and Temporal Scales

“…Together, these results provide evidence that selection as a consequence of current environmental conditions is likely more important than historical events in shaping patterns of adaptive morphological differentiation in the guppy. Selection for current environmental conditions has also been shown to be more important than vicariant events in the morphological differentiation of Anolis lizards (Losos et al 1998;Malhotra and Thorpe 2000) and rock pocket mice, Chaetodipus intermedius (Hoekstra et al 2005).…”