Population structure and genetic connectivity of the scalloped hammerhead shark across nursery grounds from the Eastern Tropical Pacific

Published on
22 February 2022

Population structure and genetic connectivity of the scalloped hammerhead shark (Sphyrna lewini) across nursery grounds from the Eastern Tropical Pacific: implications for management and conservation

Mariana Elizondo-Sancho, Yehudi Rodríguez-Arriatti, Federico J. Albertazzi, Adrián Bonilla-Salazar, Daniel Arauz, Randall Arauz, Elisa Areano, Cristopher G. Avalos-Castillo, Óscar Brenes, Elpis J. Chávez, Arturo Dominici-Arosemena, Mario Espinoza, Maike Heidemeyer, Rafael Tavares, Sebastián Hernández


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 (ETP) using both sequences of the mitochondrial DNA control region (mtCR) and nuclear-encoded microsatellite loci. 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, the mtCR data showed low levels of haplotype diversity ranged from 0.000 to 0.608, while nucleotide diversity ranged from 0.000 to 0.0015. A more fine-grade population structure analysis was detected 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.

bioRxiv, DOI: 10.1101/2022.02.22.481487


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