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.
