Résumé
For free-swimming marine species like sharks, only population genetics and
demographic history analyses can be used to assess population
health/status as baseline population numbers are usually unknown. We
investigated the population genetics of blacktip reef sharks, Carcharhinus
melanopterus; one of the most abundant reef-associated sharks and the apex
predator of many shallow water reefs of the Indian and Pacific Oceans. Our
sampling includes 4 widely separated locations in the Indo-Pacific and 11
islands in French Polynesia with different levels of coastal development.
Four-teen microsatellite loci were analysed for samples from all locations
and two mitochondrial DNA fragments, the control region and cytochrome b,
were examined for 10 locations. For microsatellites, genetic diversity is
higher for the locations in the large open systems of the Red Sea and
Australia than for the fragmented habitat of the smaller islands of French
Polynesia. Strong significant structure was found for distant locations
with FST values as high as ~0.3, and a smaller but still significant
structure is found within French Polynesia. Both mitochondrial genes show
only a few mutations across the sequences with a dominant shared haplotype
in French Polynesia and New Caledonia suggesting a common lineage
different to that of East Australia. Demographic history analyses indicate
population expansions in the Red Sea and Australia that may coincide with
sea level changes after climatic events. Expansions and flat signals are
indicated for French Polynesia as well as a significant recent bottleneck
for Moorea, the most human-impacted lagoon of the locations in French
Polynesia.