Colonization history and genetic diversity: adaptive potential in early stage invasions.

The introduction of Anolis cristatellus from the multiple species anole community of Puerto Rico in the Greater Antilles to the island of Dominica in the Lesser Antilles, with its solitary endemic anole, provides an example of a very recent, timed, single colonization. We investigate the geographic origin and adaptive potential of the Dominican population using a range of methods including mtDNA phylogeography, nuclear microsatellite variation and multiple paternity studies, as well as heritability estimates, common garden experiments and comparative geographic studies of quantitative scalation traits. Phylogeographic analysis of NADH2 and microsatellite studies suggests that the Dominican population arose from a set of individuals from the central west area of Puerto Rico within their endemic range. The multiple-individual inoculation, together with sperm storage and evidence of multiple paternity indicate genetic variability and suggest the potential for adaptation by natural selection. Estimates of heritability, common garden experiments and broad sense Q(ST)/F(ST) ratios, linked to replicated comparisons along elevational transects go some way to suggesting that the invasive populations may be adapting by natural selection, in parallel with the endemic anole, in the brief period since their introduction.

Molecular clocks and geological dates: cytochrome b of Anolis extremus substantially contradicts dating of Barbados emergence.

Even though molecular clocks vary in rate to some extent, they are widely used and very important in a range of evolutionary studies, not least in interpreting cause and colonization in phylogeography. Evolutionists may use island age and emergence to give the earliest possible date for colonization by a species and hence give the lower limit in a molecular clock calibration. The geology of the Lesser Antilles is well studied and Barbados, although composed of some ancient rocks, is thought to have emerged only about 1 million years ago (Ma). The cytochrome b mitochondrial gene is the most widely used gene in vertebrate phylogeography, and generally evolves at a rate of 1-2% per million years (Myr) for poikilothermic vertebrates. Divergence measured across almost all of this gene in the endemic anole (Anolis extremus) reveals a mean patristic distance of approximately 8.3% between this clade and its sister, together with distinct divergence and phylogeographical structure within Barbados. The divergence time, estimated by a range of procedures using four calibration points, is not in the least compatible with the proposed geological time of emergence of Barbados. Hence, either the molecular clock rate does not apply to the Barbadian anole population, or the geological dating of the emergence of Barbados is erroneous. The compatibility of geological times and molecular divergence of this complex on Martinique, together with relative rates tests comparing the rates on Barbados and Martinique, do not suggest atypical clock rates. The question of whether Barbados emerged much earlier than is currently thought, or whether the molecular clock assumptions are inappropriate, remains open.

Phylogeny, paraphyly and ecological adaptation of the colour and pattern in the Anolis roquet complex on Martinique.

Martinique is an environmentally heterogeneous island with a complex geological history. It is occupied by a solitary anole, Anolis roquet, showing marked geographical variation in colour and other features. Phylogenetic analysis of a segment (1 kb) of the mitochondrial cytochrome b gene across the Anolis roquet series in the southern Lesser Antilles and at 63 localities of Anolis roquet in Martinique indicate that A. roquet is paraphyletic as A. extremus (Barbados) is nested within the Martinique populations. Moreover, divergent phylogenetic lineages exist within Martinique (max. 10.6% uncorrected pairwise), and these lineages are closely associated with the geological history of this complex island. However, objective quantification of the spectroradiometric analysis of hue by delta analysis, together with analysis of the colour pattern, indicate that they are primarily determined by adaptation to environmental conditions, irrespective of these phylogenetic lineages. There is remarkable convergence in hue and pattern in both extreme xeric (dark chevrons on a dull, generally grey/brown, background), and montane conditions (black reticulation and non-UV white spots on a bright, saturated green background). Moreover, parallel trends occur between Martinique and other Lesser Antillean anoles, which further argues for adaptation (increase in green saturation in montane areas and higher levels of UV on the dewlap of some Atlantic forms). As an exception, there are two specific situations where anoles from different lineages look different. These are (i). in the low-altitude regions of the northwest where the northwestern and central lineages make contact, and (ii). in the far south of the island where the southern and central lineages meet.

The usefulness of amplified fragment length polymorphism markers for taxon discrimination across graduated fine evolutionary levels in Caribbean Anolis lizards.

Fine-level taxon discrimination is important in biodiversity assessment and ecogeographical research. Genomic markers are often required for studies on closely related taxa, however, most existing mitochondrial and nuclear markers require prior knowledge of the genome and are impractical for use in small conservation projects. This study describes the application of amplified fragment length polymorphism (AFLP) to discriminate at four progressively finer evolutionary levels of Caribbean Anolis lizards from the central Lesser Antilles. AFLP is shown to be a rapid and effective method for discriminating between species. Separation increases with primer pair number and choice of primer combination appears to be noncritical. Initial population-level results show markedly less discriminatory power. A screening technique for the identification of population informative markers combining principal component and principal coordinate analyses is presented and assessed. Subsequent results show selected conspecific AFLP data to be remarkably congruent with those of mitochondrial DNA, microsatellite and morphological markers. The use of AFLP as a low-cost nuclear marker in species-level taxon discrimination is supported, whereas population level application demands further consideration.

The dynamics of natural selection and vicariance in the Dominican anole: patterns of within-island molecular and morphological divergence.

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.

A phylogenetic analysis of body size evolution in the Anolis roquet group (Sauria: Iguanidae): character displacement or size assortment?

The important role that competition plays in structuring communities is well documented; however, the role of competition in an evolutionary context remains unclear. Evolutionary investigations into the role of competition have often focused on the process of character displacement, and a good example of this is the evolution of body size in the Anolis lizards of the Caribbean islands. Previous work on the A. roquet species group has taken a phylogenetic approach and concluded that patterns of body size differences are not caused by character displacement but are a result of size assortment. Using a phylogenetic reconstruction based on the sequence of the cytochrome b gene (cyt-b) and ancestral character-state reconstruction methods, we investigated the roles of character displacement and size assortment. Our results indicated that size assortment alone was insufficient to explain the observed patterns of body size differences. Furthermore, we found that change in body size was associated with a change in allopatry/sympatry, thus supporting the character-displacement hypothesis. We conclude that patterns of body size differences in the A. roquet species group appear to be the result of a combination of character displacement and size assortment because character displacement was only found to be possible on three occasions.