| dc.description.abstract | Defining demographically independent units and understanding gene flow between them is
essential for managing and conserving exploited populations. The scalloped hammerhead
shark, Sphyrna lewini, is a coastal semi-oceanic species found worldwide in tropical and
subtropical waters. Pregnant females give birth in shallow coastal estuarine habitats that
serve as nursery grounds for neonates and small juveniles, and adults move offshore and
become highly migratory. We evaluated the population structure and connectivity of S.
lewini in coastal areas across the Eastern Tropical Pacific Ocean (ETP) using both nuclearencoded microsatellite loci and sequences of the mitochondrial DNA control region
(mtCR). The mtCR defined two genetically discrete geographic groups: the Mexican
Pacific and the central-southern Eastern Tropical Pacific (Guatemala, Costa Rica, Panamá,
and Colombia). Overall, low levels of the mtCR were found; haplotype diversity ranged
from 0.000 to 0.608, while nucleotide diversity ranged from 0.000 to 0.0015. More finegrade population structure analysis was suggested using microsatellite loci where
Guatemala, Costa Rica, and Panamá differed significantly. Genetic diversity analysis with
nuclear markers revealed an observed heterozygosity ranging from 0.68 to 0.71 and an
allelic richness from 5.89 to 7.00. Relatedness analysis revealed that individuals within
nursery areas were more closely related than expected by chance, suggesting that S. lewini
may exhibit reproductive philopatric behaviour within the ETP. Findings of at least two
different management units, and evidence of philopatric behaviour call for intensive
conservation actions for this critically endangered species in the ETP. | |
