Résumé
Population genetics have been increasingly applied to study large sharks
over the last decade. Whilst large shark species are often difficult to
study with direct methods, improved knowledge is needed for both
population management and conservation, especially for species vulnerable
to anthropogenic and climatic impacts. The tiger shark, Galeocerdo cuvier,
is an apex predator known to play important direct and indirect roles in
tropical and sub-tropical marine ecosystems. While the global and
Indo-West Pacific population genetic structure of this species has
recently been investigated, questions remain over population structure and
demographic history within the Western Indian (WIO) and within the Western
Pacific Oceans (WPO). To address the knowledge gap in tiger shark regional
population structures, the genetic diversity of 286 individuals sampled in
seven localities was investigated using 27 microsatellite loci and three
mitochondrial genes (CR, COI, cytb). A weak genetic differentiation was
observed between the WIO and the WPO, suggesting high genetic
connectivity. This result agrees with previous studies, and highlights the
importance of the pelagic behaviour of this species to ensure gene flow.
Using Approximate Bayesian Computation to couple information from both
nuclear and mitochondrial markers, evidence of a recent bottleneck in the
Holocene (2,000-3,000 years ago) was found, which is the most probable
cause for the low genetic diversity observed. A contemporary effective
population size as low as 111 [43,369] was estimated during the
bottleneck. Together, these results indicate low genetic diversity that
may reflect a vulnerable population sensitive to regional pressures.
Conservation measures are thus needed to protect a species that is
classified as Near Threatened.