Résumé
Knowledge of population structure, connectivity and effective population
size remains limited for many marine apex predators, including the bull
shark Carcharhinus leucas. This large-bodied coastal shark is distributed
worldwide in warm temperate and tropical waters, and uses estuaries and
rivers as nurseries. As an apex predator, the bull shark likely plays a
vital ecological role within marine food webs, but is at risk due to
inshore habitat degradation and various fishing pressures. We investigated
the bull shark’s global population structure and demographic history by
analysing the genetic diversity of 370 individuals from 11 different
locations using 25 microsatellite loci and three mitochondrial genes (CR,
nd4, cytb). Both types of markers revealed clustering between sharks from
the Western Atlantic and those from the Western Pacific and the Western
Indian Ocean, with no contemporary gene flow. Microsatellite data
suggested low differentiation between the Western Indian Ocean and the
Western Pacific, but substantial differentiation was found using
mitochondrial DN A. Integrating information from both types of markers and
using Bayesian computation with a random forest procedure (ABC-RF), this
discordance was found to be due to a complete lack of contemporary gene
flow. High genetic connectivity was found both within the Western Indian
Ocean and within the Western Pacific. In conclusion, these results suggest
important structuring of bull shark populations globally with important
gene flow occurring along coastlines , highlighting the need for
management and conservation plans on regional scales rather than oceanic
basin scale.