Evolutionary history ofTrachylepisskinks in the Seychelles islands: introgressive hybridization, morphological evolution and geographic structure

Abstract

The Seychelles is a remarkably interesting archipelago for evolutionary studies, but only recently have molecular markers been used to explore its biogeographic patterns. Here we used morphological and molecular data to examine diversity and phylogenetic relationships of two endemic skink sister-species from this archipelago: Trachylepis sechellensis and Trachylepis wrightii. Mitochondrial DNA genealogy rendered a monophyletic T. wrightii nested within a paraphyletic T. sechellensis, whereas nuclear DNA sequences from five unlinked markers reflected the accepted taxonomy. Hybridization and massive mtDNA introgression leading to the complete replacement of the native mtDNA lineage of T. sechellensis in some of the islands were invoked to explain this result, and morphological variation also seemed to reflect this pattern of reticulation. A Mio-Pliocene divergence between both species is suggested. Multilocus molecular data were used to uncover biogeographic patterns within the archipelago, which reflected shared patterns with other co-distributed lizard taxa; specifically a north-south marked structure, a close relationship between populations from Fregate and the southern islands, and a detectable isolation within the southern group, between Mah e, and Silhouette and North Islands. Gene flow from these latter islands towards the northern group was also suggested. These results add to the growing body of evidence of the influence of geographic distance and sea-level oscillations in shaping the genetic structure of Seychellois taxa and of the existence of common biogeographic patterns across the archipelago.

The roles of vicariance and isolation by distance in shaping biotic diversification across an ancient archipelago: evidence from a Seychelles caecilian amphibian

“…The spatial structuring of phenotypic and genetic variation within H. rostratus (especially the partitioning into northern-and southern-island groups) is broadly similar to that observed within Seychelles lizards (38,(43)(44)(45)82,83), frogs (39,47) and crabs (46). This spatial (and temporal) pattern is likely caused by rising sea levels sundering formerly widespread populations and/or IBD across Association between the different datasets (Table 3) strongly supports the general patterns of genetic and morphological variation being explained by isolation-by-distance (IBD) rather than isolation-by-adaptation (IBA) within H. rostratus.…”

Endemic, endangered and evolutionarily significant: cryptic lineages in Seychelles’ frogs (Anura: Sooglossidae)

“…1). This pattern of differentiation is documented in studies across a range of taxa, including the geckos Ailuronyx (Rocha et al, 2016a), Phelsuma (Rocha et al, 2013), Urocotyledon (Rocha et al, 2011); and the skinks Pamelaescincus (Valente et al, 2013) and Trachylepis (formerly Mabuya) (Rocha et al, 2016b). However, within this north-south biogeographic pattern, further evidence of cryptic diversity is beginning to emerge in several taxa (e.g.…”

“…Recently identified phylogeographic patterns within the archipelago's endemic herpetofauna have revealed a variety of geographic correlations: skinks and geckos broadly differentiate into northern (Praslin and surrounding islands) and southern (Mahé, Silhouette, and surrounding islands) groups (Rocha et al, 2010;Rocha et al, 2011;Valente et al, 2013;Rocha et al, 2016a;Rocha et al, 2016b); while for the nonsooglossid anurans, a distinct lack of variability is shown in the multi-distributed treefrog Tachycnemis seychellensis (Maddock et al, 2014), conflicting with observed structuring in Seychelles endemic caecilians (Adamson et al, 2016;Maddock et al, 2016;Maddock et al, 2017). Our mtDNA analyses appear to confirm the relationship posited by Taylor et al (2012), namely that Silhouette and Praslin populations of So.…”

“…However, within this north-south biogeographic pattern, further evidence of cryptic diversity is beginning to emerge in several taxa (e.g. Rocha et al, 2016b). The discovery of a previously unknown population of sooglossid frogs on the island of Praslin-where the frogs had hitherto been unrecorded-and identification of this population as an evolutionarily significant unit (ESU) (Taylor et al, 2012) provided the motivation to assess the genetic diversity of this family.…”

Population genetic structure and evolutionary history of Bale monkeys (Chlorocebus djamdjamensis) in the southern Ethiopian Highlands

“…The BSP model assumes a single panmictic population and violation of this assumption can result in misleading demographic inferences [ 72 , 73 ]. Although BSP assumes a single species or monophyletic group in analyses of demographic history, similar analyses have been carried out when modelling hybridization at population peripheries [ 74 , 75 ]. Thus, we generated BSPs for genetically homogenous geographic populations as inferred by AMOVA (e.g., [ 34 , 74 , 75 ]).…”