Molecular species identification and spatio-temporal assessment of genetic diversity in the smooth hammerhead shark Sphyrna zygaena in South Africa

[摘要] ENGLISH ABSTRACT: The South African coast hosts a unique oceanographic regime with an enriched habitat able to support a diverse biota of chondrichthyans (sharks, skates, rays and chimaeras). Investigating these species and populations on a molecular level could aid in conserving this rich chondrichthyan biodiversity. As a precursor, a case study regarding the composition of species in three different South African fisheries was evaluated to determine the utility of the mitochondrial cytochrome oxidase subunit 1 (CO1) gene in delimiting species identity. Through this, a number of issues surrounding misidentification and cryptic speciation were recognized, and the efficacy of CO1 was tested and proved to be useful in identifying chondrichthyans affected in South African fisheries. One of these species, the smooth hammerhead shark (Sphyrna zygaena) displays a high degree of site fidelity to Mossel Bay as evidenced by the rise in the number of neonate and juvenile hammerheads during the summer season. This species is vulnerable as they are in danger of overfishing and the destruction of their natural habitat. With a low fecundity and a long generational time, recovery of near-depleted populations is prolonged. In this study mitochondrial sequence data and microsatellite markers were used to assess genetic diversity within and between S. zygaena sampling cohorts collected from Mossel Bay to the KwaZulu Natal coast. Additionally, kinship between the juvenile individuals was determined and parental genotypes were reconstructed from the neonate and juvenile smooth hammerhead sharks sampled in the Mossel Bay area.Significant population subdivision was evident between individuals sampled in the warm temperate south coast (Mosselbay) and the subtropical east coast (Algoa Bay and KwaZulu Natal), with asymmetric gene flow mainly from the south to the east coast. Highly significant population differentiation was seen between sampling years, indicative of differential temporal stocks utilizing Mossel Bay each year. Analysis of kinship revealed a high degree of sibling relationships within and between seasons, which is likely due to an overlap of some parental genotypes across seasons. The results obtained here can assist with decisions regarding the conservation of chondrichthyan biodiversity in South Africa while it is also recommended that genetic structure and temporal variation of S. zygaena populations be evaluated on a finer scale in the future.

[发布机构] Stellenbosch University