Abstract
BackgroundLying in a shallow continental shelf cyclically affected by oscillating sea levels since the Miocene, the Seychelles islands are particularly interesting for evolutionary studies. Recent molecular studies are generating an emerging picture of the origin of its biota, yet very little is known regarding their phylogeographic structure or on the factors promoting diversification within the archipelago. Here we aimed to obtain a detailed depiction of the genetic structure and evolution of one of the most widespread vertebrate groups in the archipelago: the day-geckos of the genus Phelsuma. In parallel, we aimed to infer divergence times between species and subspecies, testing a long-standing hypothesis that argues for different time since sympatry between species as the cause of their different morphological differentiation across the archipelago.ResultsMolecular data corroborated the existence of two main lineages, corresponding to the two currently recognized species. Divergences between species likely date back to the Mio-Pliocene, while more recent, Pleistocenic, divergences are suggested within each species. Populations from outer islands share mtDNA haplotypes with inner island populations, suggesting very recent dispersals (or introductions). We found no evidence of current gene flow between species, but results pointed to the possibility of gene flow between (now allopatric) subspecies. Time estimates suggest a synchronous divergence within each species (between island groups).ConclusionsThe geographic patterns of genetic variation agree with previous taxonomic subdivisions within each species and the origin of outer islands populations is clearly tracked. The similar intraspecific divergence time estimates obtained suggest that the differential body-size differentiation between species within each group of islands may be driven by factors other than character displacement proportional to time since sympatry, as previously suggested. These factors could include different habitats/resources available within each island group, niche differentiation and/or character displacement. We also bring again into consideration the hypothesis of body size being influenced by the distribution of native vegetation and social systems within this group, although it remains to be tested. Our results highlight not only the necessity of clarifying the role of ecology and interspecific interactions in this group’s morphological diversification and community assemblage, but also the importance of co-evolutionary mechanisms and their importance for appropriate conservation of island biodiversity. Further, we provide a detailed description of the phylogeographic structure of these taxa across these islands, which still remain poorly characterized in this respect.
Highlights
Lying in a shallow continental shelf cyclically affected by oscillating sea levels since the Miocene, the Seychelles islands are interesting for evolutionary studies
That is true for the Seychelles, where only a handful of studies have explored the genetic structure of different species within the archipelago [8,9,10,11,12,13]
Mitochondrial DNA variability and genetic structure The two species, P. sundbergi and P. astriata correspond to two divergent mtDNA clades (Figure 2) (Nei’s Da = 11%)
Summary
Lying in a shallow continental shelf cyclically affected by oscillating sea levels since the Miocene, the Seychelles islands are interesting for evolutionary studies. Recent molecular studies are generating an emerging picture of the origin of its biota, yet very little is known regarding their phylogeographic structure or on the factors promoting diversification within the archipelago. While there is an emerging picture from molecular data about the origin of their biota (see [2,3,4,5,6,7] for recent reviews), diversification mechanisms within each archipelago and island are less understood. The granitics are a group of about 40, clustered together on the undersea shelf of granite, that is the Seychelles bank. These comprise the islands of North, Silhouette, Mahé, Fregate, Praslin, La Digue, Curieuse and several smaller ones encircling them. The raised coralline islands (Aldabra, Assumption, Astove and Cosmoledo) are oceanic, formed by reef-building corals acting on submerged volcanic seamounts that may have formed some 20 million years ago (Mya) [15] and were submerged and re-emerged several times since their formation
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