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The West Indies have been the focus of considerable interest in the fields of ecology, biogeography and evolutionary biology (Hedges, 1996; Ricklefs & Bermingham, 2008), not least because of their very high species diversity and endemism. There are several spectacular radiations in this archipelago, the most well studied being that of Anolis lizards (Roughgarden, 1995; Losos, 2009). Other less-studied groups in this region with impressive diversification include the extinct megalonychid sloths (White & MacPhee, 2001), the largely extinct capromyid rodents (Woods, 1989), the eleutherodactyline frogs (Heinicke et al., 2007) and the sphaerodactyline geckos (Gamble et al., 2008).
The West Indies are generally considered as being composed of two major geographic and geological entities. The Greater Antilles are old fragments of continental crust, while the Lesser Antilles are of more recent origin, forming a double volcanic arc at the boundary between the Caribbean plate and the North Atlantic ocean floor (Maury et al., 1990). The eastern outer arc was active from the Eocene to mid-Oligocene, while the western arc started its activity in the early Miocene and is still active today (Maury et al., 1990). While the Greater Antilles may have been connected to Central America by land bridges, the Lesser Antilles never had such a connection with the continent. Moreover, most of these islands have never been connected to each other, which implies that over-water dispersal was, and is, the route for colonization of these islands (Hedges, 1996). The alternative hypothesis of the existence of a land bridge between South America and Cuba (the GAARlandia hypothesis; Iturralde-Vinent & MacPhee, 1999) is generally not supported by the timing of the diversification of Caribbean taxa (Hedges, 2006; Ali, 2012; but see Alonso et al., 2011).
Geckos from the genus Sphaerodactylus comprise about 100 species distributed in the Caribbean Islands and adjacent continental areas. Most of this diversity, about 80 species, is in the West Indies, rendering this one of the most diverse vertebrate genera in the area (Schwartz & Henderson, 1991; Hedges, 1996). All species of Sphaerodactylus are typically very small, Sphaerodactylus ariasae being the smallest described terrestrial amniote (Hedges & Thomas, 2001). They generally inhabit leaf litter in a wide range of habitats. Phylogenetic relationships within West Indian species have been investigated using immunological and allozyme data (Hass, 1991) and mitochondrial DNA (mtDNA) sequences (Hass, 1996), but Lesser Antillean species (nine species) have been under-represented in these studies. Most species of Sphaerodactylus are endemic to one island, or even to a limited region within an island (Hass, 1996), but a few species of Sphaerodactylus from the Lesser Antilles are known to have a wider range and inhabit several adjacent islands. However, in these more widespread nominal species, high divergence suggests that they may contain forms worthy of recognition as distinct species (Thorpe et al., 2008a). This high within-species divergence, allied to their extremely small size and secretive behaviour, may have led to an underestimation of the real number of species. Close investigation may therefore reveal cryptic diversity, as exemplified in a recent study of Sphaerodactylus fantasticus, where an extremely high molecular divergence between some of the islands of Les Saintes has led to the recognition of Sphaerodactylus phyzacinus as a distinct species (Thorpe et al., 2008a).
In this study we investigate the phylogeny and biogeography of another widespread Sphaerodactylus species: Sphaerodactylus vincenti Boulenger, 1891. This relatively large-sized sphaerodactyl gecko (snout–vent length up to 40 mm) is distributed in the central/southern Lesser Antilles on the islands of Dominica, Martinique, St Lucia and St Vincent. A phylogenetic study of the Lesser Antilles Sphaerodactylus species based on 430 bp of the cytochrome b suggested that its closest relatives are Sphaerodactylus kirbyi from the Grenadines, just south of St Vincent, and Sphaerodactylus microlepis from St Lucia (Ogden, 2002). The colour pattern is highly variable and nine subspecies have been described (see Appendix S1 in Supporting Information). This superficial morphological diversity is highest on Martinique, which has six subspecies (Schwartz, 1964). Schwartz (1964) hypothesized that this island is the centre of origin of the species and that St Lucia and St Vincent were colonized from southern Martinique populations, while Dominica was colonized from northern Martinique populations. The high colour-pattern diversity observed in Martinique may be the result of the complex geological history of this island, or adaptation to the pronounced environmental zonation on Martinique (Thorpe et al., 2008b, 2010).
Martinique is composed of both younger and older arc elements. The Caravelle and Sainte Anne peninsulas have an older arc origin, whereas the rest of the island has a more recent origin. It is thought that the different parts of Martinique (Andreieff et al., 1976; Maury et al., 1990) were originally separate islands that merged through the uplifting of a central region in a scenario broadly compatible with that illustrated in Thorpe et al. (2008b). This complex history has had a profound impact on the molecular genetic diversity of another lizard, Anolis roquet, where very divergent lineages evolved in allopatry on distinct proto-islands before coming into secondary contact once the islands coalesced (Thorpe & Stenson, 2003; Thorpe et al., 2008b, 2010). However, with this anole and other Lesser Antillean anoles, it is generally adaptation to the environmental zonation that determines its appearance (colour and pattern) and traditional subspecies (Thorpe & Stenson, 2003), rather than these geo-historical processes (Thorpe et al., 2008b).
Here we construct a phylogeny of S. vincenti across most of its distribution range to elucidate the inter-island colonization sequence. Furthermore, we use the new statistical phylogeographic tool of likelihood framework analysis (LFA) to test probabilistically the location of the ancestors of the different lineages in relation to the proto-islands that formed present-day Martinique. We also compare this phylogeographic history on Martinique with that of the sympatric anole A. roquet.
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Appendix S1 Conventional subspecies of the Sphaerodactylus vincenti/kirbyi complex.
Appendix S2 (a) List of specimens used in this study with locality and GenBank accession numbers. (b) Images of males and females of Sphaerodactylus vincenti and S. festus.
Appendix S3 beast tree for the Anolis roquet complex.
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