Abstract
BackgroundIsland systems offer excellent opportunities for studying the evolutionary histories of species by virtue of their restricted size and easily identifiable barriers to gene flow. However, most studies investigating evolutionary patterns and processes shaping biotic diversification have focused on more recent (emergent) rather than ancient oceanic archipelagos. Here, we focus on the granitic islands of the Seychelles, which are unusual among island systems because they have been isolated for a long time and are home to a monophyletic radiation of caecilian amphibians that has been separated from its extant sister lineage for ca. 65–62 Ma. We selected the most widespread Seychelles caecilian species, Hypogeophis rostratus, to investigate intraspecific morphological and genetic (mitochondrial and nuclear) variation across the archipelago (782 samples from nine islands) to identify patterns and test processes that shaped their evolutionary history within the Seychelles.ResultsOverall a signal of strong geographic structuring with distinct northern- and southern-island clusters were identified across all datasets. We suggest that these distinct groups have been isolated for ca. 1.26 Ma years without subsequent migration between them. Populations from the somewhat geographically isolated island of Frégate showed contrasting relationships to other islands based on genetic and morphological data, clustering alternatively with northern-island (genetic) and southern-island (morphological) populations.ConclusionsAlthough variation in H. rostratus across the Seychelles is explained more by isolation-by-distance than by adaptation, the genetic-morphological incongruence for affinities of Frégate H. rostratus might be caused by local adaptation over-riding the signal from their vicariant history. Our findings highlight the need of integrative approaches to investigate fine-scale geographic structuring to uncover underlying diversity and to better understand evolutionary processes on ancient, continental islands.
Highlights
Island systems offer excellent opportunities for studying the evolutionary histories of species by virtue of their restricted size and identifiable barriers to gene flow
Molecular data Mitochondrial and nuclear DNA sequence data Based on variation in 700 bp of the mitochondrial encoded cytochrome b gene we identified 34 unique haplotypes among 100 H. rostratus individuals sampled from nine islands
The sharing of some haplotypes between islands could be indicative of shared ancestry and/or of some migration having occurred in the recent past between islands
Summary
Island systems offer excellent opportunities for studying the evolutionary histories of species by virtue of their restricted size and identifiable barriers to gene flow. Islands have had an important influence on the understanding of diversification and adaptive evolution since the landmark publication of “On The Origin of Species by Means of Natural Selection” [1] see [2] These systems have been the focus of numerous evolutionary studies in part because they are tractable for investigating the consequences of evolutionary processes such as random genetic drift, founder effects and local adaptation e.g. The granitic islands are of continental origin [16], and are mountain-top remnants of the largely submerged Seychelles Microcontinent (“Seychellea” of [17]) that once formed part of the supercontinent Gondwanaland These ancient remnants were isolated by the separation from Africa of a landmass (Indigascar of [18]) consisting of Madagascar, Seychelles and India [19,20,21,22,23,24]; with the Seychelles becoming fully separated approximately 65–62 Ma [24, 25]. The granitic Seychelles are considered the emergent parts of an isolated continental block [33]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call