Genomic assessment of global population structure in a highly migratory and habitat versatile apex predator, the tiger shark (Galeocerdo cuvier)

Understanding the population dynamics of highly mobile, widely
distributed, oceanic sharks, many of which are overexploited, is necessary
to aid their conservation management.  We investigated the global
population genomics of tiger sharks (Galeocerdo cuvier), a circumglobally
distributed, apex predator displaying remarkable behavioral versatility in
its diet, habitat use (near coastal, coral reef, pelagic), and individual
movement patterns (spatially resident to long-distance migrations).
 We genotyped 242 tiger sharks from 10 globally distributed
locations at more than 2000 single nucleotide polymorphisms. Although this
species often conducts massive distance migrations, the data show strong
genetic differentiation at both neutral (FST=0.125-0.144) and candidate
outlier loci (FST=0.570-0.761) between western Atlantic and Indo-Pacific
sharks, suggesting the potential for adaptation to the environments
specific to these oceanic regions. Within these regions, there
was mixed support for population differentiation between northern and
southern hemispheres in the western Atlantic, and none for structure
within the Indian Ocean. Notably, the results demonstrate a low level of
population differentiation of tiger sharks from the remote Hawaiian
archipelago compared to sharks from the Indian Ocean (FST=0.003-0.005,
P<0.01). Given concerns about biodiversity loss and marine
ecosystem impacts caused by overfishing of oceanic sharks in the midst of
rapid environmental change, our results suggest it imperative that
international fishery management prioritize conservation of the
evolutionary potential of the highly genetically differentiated Atlantic
and Indo-Pacific populations of this unique apex predator. Furthermore, we
suggest targeted management attention to tiger sharks in the Hawaiian
archipelago based on a precautionary biodiversity conservation
perspective.