Cryptic diversity within the endemic prehensile-tailed geckoUrocotyledon inexpectataacross the Seychelles Islands: patterns of phylogeographical structure and isolation at the multilocus level

Abstract

The deciphering of the process of genetic differentiation of species with insular distributions is relevant for biogeographical and conservation reasons. Despite their importance as old gondwanic islands and part of the western Indian Ocean biodiversity hotspot, little is known about the genetic structure of taxa from the Seychelles Islands. We have examined the patterns of structure and isolation within Urocotyledon inexpectata (Reptilia: Geckkonidae), an endemic species from this archipelago. Genetic diversity was screened from populations across the archipelago for both mitochondrial and nuclear genes. Gene genealogies and model-based inference were used to explore patterns and timings of isolation between the main lineages. High levels of genetic diversity were found for the mitochondrial and some of the nuclear markers. This species harbours at least two highly differentiated lineages, exclusively distributed across the northern and southern groups of the islands. The main split between these was dated back to the Miocene-late Pliocene, but isolation events throughout the Pliocene and Pleistocene were also inferred. Migration between groups of islands was apparently nonexistent, except for one case. The low dispersal capabilities of this species, together with the intrinsic fragmented nature of its geographical distribution, seem to have resulted in highly structured populations, despite the cyclic periods of contact between the different island groups. These populations may currently represent more than one species, making U. inexpectata another example of a morphologically cryptic lineage with deep genetic divergence within gekkonids. The observed patterns suggest a hypothetical biogeographic scenario (of a main north-south phylogeographic break) for the Seychelles that can be further tested with the exploration of the phylogeographic structure of other Seychellois taxa.

Recognition of two new species of freshwater crabs from the Seychelles based on molecular evidence (Potamoidea : Potamonautidae)

“…The oscillating sea level changes during the Pliocene and Pleistocene epochs in the Seychelles were characterised by cyclic periods of contact and isolation between different groups of islands (Rocha et al 2011). When freshwater crabs first reached the Seychelles between 2.5 and 5.3 MY ago sea levels oscillated between 30 m below and 20 m above their present levels, but Silhouette was separated from Mahé throughout this time by a deep ocean channel ( Fig.…”

“…Silhouette is separated from Mahé by a deep ocean and these two islands would not have formed a single landmass even during the Pleiocene (2.5 to 5.3 MY ago) when sea levels oscillated between 30 m below and 20 m above their present levels. However, Silhouette would have been connected to the rest of the Seychelles Bank during the Pleistocene (2.5 MY ago to 11 700 years ago) when sea levels oscillated between 80 m and 30 m below their present levels (Rocha et al 2011).…”

“…It is noteworthy that the crabs on Frégate are most closely related to those on Mahé (almost 60 km away) rather than to S. alluaudi on the closer northern islands of Praslin or La Digue (33 km and 29 km from Frégate respectively). Mahé and Frégate would have been connected to Praslin and La Digue as part of the Seychelles Bank during the Pleistocene (2.5 MY ago to 11 700 years ago), when sea levels oscillated between 80 m and 30 m below their present levels (Rocha et al 2011). However, the existence of former land connections alone does not explain why the populations of freshwater crabs from the southern islands of Mahé and Frégate form one clade and why crabs from the northern islands of Praslin and La Digue form a different clade (Fig.…”

“…The presence of freshwater crabs on oceanic islands is usually explained by overseas dispersal across a saltwater barrier (Rodríguez and López 2003;Cook et al 2008b;Cumberlidge 2008a;Yeo et al 2008;Klaus et al 2009;Klaus et al 2010;Jesse et al 2010), while the presence of freshwater crabs on continental shelf islands is explained by overland dispersal during past periods of low sea levels (Cumberlidge 2008a;Rocha et al 2011). The discovery by that the colonization of the Seychelles by deckeniine freshwater crabs from Africa happened relatively recently in the late Miocene/Pliocene (between 8.7-2.3 MY ago) supports hypotheses of recent overseas dispersal Cumberlidge et al 2008;Cumberlidge 2008a;) over hypotheses of ancient Gondwanan vicariance (over 180 MY ago) (Ng et al 1995).…”

“…1). During the past 6 million years these islands have been subjected to a series of oscillating sea levels that have either exposed or submerged substantial parts of the land area of the Seychelles, with only the highest points remaining continuously dry (Rocha et al 2011). estimated that freshwater crabs first arrived on the archipelago (on Silhouette) between 2.73 and 6.0 MY ago and dispersed to the other islands within the Seychelles during the Pleistocene (1.18-1.41 MY ago).…”