Biogeographic origins of the viviparous sea snake assemblage (Elapidae) of the Indian Ocean

Kanishka D.B Ukuwela,Michael S.Y Lee,Anslem De Silva,Arne R Rasmussen,Kate L Sanders

doi:10.4038/cjs.v46i5.7457

Abstract

One of the primary goals in biogeography is to understand how different biotas have been assembled in different regions of the world. The presence of the viviparous sea snakes in the Indian Ocean (IO) poses a unique question in this regard due to their evolutionary origins in Australasia (Australia and New Guinea). Here, we examined the origins and patterns of colonization of the IO sea snake assemblage through time-calibrated molecular phylogenies and ancestral area reconstructions. We further evaluated how past and present barriers to dispersal affect genetic diversity of IO sea snakes by examining the population genetic structure of the widespread sea snake, Hydrophis curtus . Our phylogenetic analyses and ancestral area reconstructions strongly indicate that the majority of the IO sea snakes are derived from the Southeast Asian (SEA) sea snake fauna through dispersal and colonization with an in situ radiation ( Hydrophis stricticollis-Hydrophis obscurus clade). Further, many species have undergone vicariant speciation events across the Sunda shelf/Indo-Pacific barrier, which formed during the low sea level periods of the Pleistocene. Population genetic analysis of H. curtus revealed a prominent genetic break between populations broadly distributed in the IO and SEA with limited recent gene flow indicating possible cryptic species. These results suggest that compared to the viviparous sea snake stem group that originated 10.6-6.5 million years ago, the IO viviparous sea snakes have a relatively long and complex evolutionary history in the IO and thus have a unique conservation value.

Highlights

The tropical coastal regions of the Indian Ocean (IO) is home to an assemblage of marine biodiversity that is second in the total number of species only to the Indo-Australian Archipelago (IAA) in the West Pacific (WP) (Tittensor et al, 2010)
All three AAR analyses indicate that the majority of IO sea snakes (12 species: Microcephalophis (Hydrophis) gracilis, Hydrophis caerulescens, H. cyanocinctus, H. (Lapemis) curtus, H. fasciatus, H. (Kerilia) jerdoni, H. ornatus, H. (Pelamis) platurus, H. spiralis, H. (Enhydrina) schistosus, Figure 2: Time-calibrated tree of viviparous sea snakes, with Bayesian (BEAST) ancestral area reconstructions
Our findings indicate that dispersal and colonization from Southeast Asian (SEA) is the major source of viviparous sea snake diversity in the IO

Summary

Introduction

The tropical coastal regions of the IO is home to an assemblage of marine biodiversity that is second in the total number of species only to the Indo-Australian Archipelago (IAA) in the West Pacific (WP) (Tittensor et al, 2010). Several hypotheses/models have been proposed to explain the exceptional diversity found in marine biodiversity hotspots in the tropical regions. The best known is the ‘centre of’ models (i.e. centre of speciation, accumulation, overlap) that have been frequently invoked to explain the exceptional diversity of the IAA (Bowen et al, 2013). The centre of speciation hypothesis (Ekman, 1953) suggests that marine biodiversity hotspots produce new species at higher rates and act as cradles for speciation. Peripheral areas adjacent to marine biodiversity hotspots are considered to be evolutionary net sinks in which colonizers arrive and evolve to new endemic species, but do not disperse and speciate beyond these regions (Bowen et al, 2013). The centre of overlap model, predicts that ranges of co-distributed species overlap in central regions resulting in higher species diversity than the peripheries (Woodland, 1983)

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