Like a rolling stone: colonization and migration dynamics of the grey
reef shark (Carcharhinus amblyrhynchos)
Abstract
Designing appropriate management plans requires knowledge of both the
dispersal ability and what has shaped the current distribution of the
species under consideration. Here we investigated the evolutionary
history of the endangered grey reef shark (Carcharhinus
amblyrhynchos) across its range by sequencing thousands of RAD-seq loci
in 173 individuals in the Indo-Pacific (IP) . We first bring evidence of
the occurrence of a range expansion (RE) originating close to the
Indo-Australian Archipelago (IAA) where two stepping-stone waves (east
and westward) colonized almost the entire IP. Coalescent modeling
additionally highlighted a homogenous connectivity
(Nm~10 per generation) throughout the range, and
an isolation by distance model suggested the absence of barriers to
dispersal despite the affinity of C. amblyrhynchos to coral
reefs. This coincides with long-distance swims previously recorded,
suggesting that the strong genetic structure at the IP scale (FST
~ 0.56 between its ends) is the consequence of its broad
current distribution and organization in a large number of demes. Our
results strongly suggest that management plans for the grey reef shark
should be designed on a range-wide rather than a local scale due to its
continuous genetic structure. We further contrasted these results with
those obtained previously for the sympatric but strictly
lagoon-associated Carcharhinus melanopterus, known for its
restricted dispersal ability. C. melanopterus exhibits similar RE
dynamic, but is characterized by stronger genetic structure and a
non-homogeneous connectivity largely dependent on local coral reefs
availability. This sheds new light on shark evolution, emphasizing the
roles of IAA as source of biodiversity and of life history traits in
shaping the extent of genetic structure and diversity.