Structure and phylogeography of two tropical predators, spinner (Stenella longirostris) and pantropical spotted (S. attenuata) dolphins, from SNP data.

Matthew S Leslie,Phillip A Morin

doi:10.1098/rsos.171615

Abstract

Little is known about global patterns of genetic connectivity in pelagic dolphins, including how circumtropical pelagic dolphins spread globally following the rapid and recent radiation of the subfamily delphininae. In this study, we tested phylogeographic hypotheses for two circumtropical species, the spinner dolphin (Stenella longirostris) and the pantropical spotted dolphin (Stenella attenuata), using more than 3000 nuclear DNA single nucleotide polymorphisms (SNPs) in each species. Analyses for population structure indicated significant genetic differentiation between almost all subspecies and populations in both species. Bayesian phylogeographic analyses of spinner dolphins showed deep divergence between Indo-Pacific, Atlantic and eastern tropical Pacific Ocean (ETP) lineages. Despite high morphological variation, our results show very close relationships between endemic ETP spinner subspecies in relation to global diversity. The dwarf spinner dolphin is a monophyletic subspecies nested within a major clade of pantropical spinner dolphins from the Indian and western Pacific Ocean populations. Population-level division among the dwarf spinner dolphins was detected—with the northern Australia population being very different from that in Indonesia. In contrast to spinner dolphins, the major boundary for spotted dolphins is between offshore and coastal habitats in the ETP, supporting the current subspecies-level taxonomy. Comparing these species underscores the different scale at which population structure can arise, even in species that are similar in habitat (i.e. pelagic) and distribution.

Highlights

High dispersal potential in marine organisms is thought to promote connectivity and evolutionary stasis in geographically distant populations [1]
Before conducting the discriminant analysis of principal components (DAPC) analyses, we examined the cumulative variance explained by the eigenvalues for the full range of principal components
Subsequent studies should include the Atlantic pantropical spotted dolphin samples, and samples from northern Australia should be added to test the circumtropical biogeographic hypotheses in this species. Both spinner and spotted dolphins appear to have tightly clustered Indo-western Pacific core relationships characterized by recent divergences, incomplete lineage sorting and/or ongoing gene flow

Summary

Introduction

High dispersal potential in marine organisms is thought to promote connectivity and evolutionary stasis in geographically distant populations [1]. Several major barriers to gene flow help shape various patterns of population genetic structure. These barriers include the open east Pacific basin, the Isthmus of Panama, the broad mid-Atlantic, and the Indo-Pacific barrier formed by the Indo-Malay Archipelago [3,4]. Ephemeral barriers may be present during some periods of deep time, but not others. This is almost certainly the case with the Benguela barrier of southern Africa, reflected in an Atlantic and Indo-Pacific connection in some species (summarized by Bowen et al [3]). Generalizations across pelagic population structure of predatory fishes are difficult to draw because of the complex mosaic of factors that contribute to form the patterns observed, including demography, vagility, migration, extinction, recolonization, etc

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