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The Southwestern Indian Ocean as a potential marine evolutionary hotspot: perspectives from comparative phylogeography of reef brittle-stars

Authors

  • Thierry B. Hoareau,

    Corresponding author
    1. Molecular Ecology and Evolution Programme, Department of Genetics, University of Pretoria, Pretoria, South Africa
    2. Université de La Réunion, Laboratoire ECOMAR – FRE CNRS 3560, Labex CORAIL, Saint-Denis, La Réunion, France
    • Correspondence: Thierry B. Hoareau, Department of Genetics, University of Pretoria, Private bag X20, Hatfield, 0028, South Africa.

      E-mail: thoareau@gmail.com

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  • Emilie Boissin,

    1. Molecular Ecology and Evolution Programme, Department of Genetics, University of Pretoria, Pretoria, South Africa
    2. USR3278-CRIOBE-CNRS-EPHE, Laboratoire d'excellence ‘CORAIL’, Université de Perpignan-CBETM, Perpignan Cedex, France
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  • Gustav Paulay,

    1. Florida Museum of Natural History, Gainesville, FL, USA
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  • J. Henrich Bruggemann

    1. Université de La Réunion, Laboratoire ECOMAR – FRE CNRS 3560, Labex CORAIL, Saint-Denis, La Réunion, France
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Abstract

Aim

The global biodiversity crisis requires the identification of regions with high evolutionary potential, i.e. evolutionary hotspots (evospots). We created an analytical framework based on comparative phylogeography and coalescent methods to assess the dynamics of diversification and population persistence in the reef ecosystem of a little-studied region: the Southwestern Indian Ocean (SWIO).

Location

Coral reefs of the SWIO, with comparative data from the Pacific Ocean.

Methods

We generated sequences of mitochondrial DNA (COI and 16S) for 10 widespread brittle-stars (345 specimens) from 21 localities (8 in the SWIO). We analysed them by combining comparative phylogeography approaches, coalescent-based methods, molecular clocks and the concept of evolutionarily significant units (ESUs) to draw conclusions about the drivers of biodiversity in the region.

Results

Cryptic diversity was prevalent, increasing lineage diversity within the 10 nominal species by 70% within the SWIO and by 200% across the Indo-West Pacific. All seven new SWIO lineages meet the criteria for ESUs and at least six are biological species. We detected likely intraregional diversifications dating to the Plio-Pleistocene, supporting the SWIO as a generator of biodiversity. Geographical restriction of ESUs, long coalescent times (> 80 ka) and old in situ diversification (> 1 Ma) point to the persistence of populations over multiple glacio-eustatic cycles. We provide data suggesting demographic expansion during sea-level high stands. Regional connectivity was lower, and cryptic differentiation higher in lecithotrophs than in planktotrophs.

Main conclusions

The analytical framework based on a biodiversity survey makes it possible to identify evospots by assessing the potential of a region to maintain and generate biodiversity and by evaluating the evolutionary processes and potential drivers at play.

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