A Genetic Study Of Two Inshore Dolphin Species (Cephalorhynchus Heavisidii And Tursiops Aduncus) Found Along The Coast Of South Africa

Abstract

Genetic parameters such as genetic variability, gene flow, relatedness and migration were determined between two South African coastal delphinid species, Cephalorhynchus heavisidii (Heaviside’s dolphin) and Tursiops aduncus (Indo-Pacific Bottlenose dolphin), in order to contribute towards designing efficient conservation management strategies. The molecular markers used in this study include the mitochondrial DNA control region (mtDNA) and several microsatellite loci that were chosen from existing dolphin primer sets which also proved to crossamplify on additional cetacean species. The population structure and gene flow investigated for Heaviside’s dolphins across seven sampling sites (n = 395) revealed contrasting results. Mitochondrial DNA suggested six populations within the range studied (ФST = 0.15611, P < 0.0001), whilst microsatellite data identified only two populations and differed with respect to the relative levels of specific pairwise population differentiation comparisons. Neutrality tests of the mitochondrial sequences combined to the mismatch distribution analysis, pointed towards a population expansion at the two geographic extremes (Table Bay and Walvis Bay), whereas bottleneck tests suggest a bottleneck in the northern population (Lamberts Bay, Hondeklipbaai, Port Nolloth, Luderitz, and Walvis Bay). Genetic relatedness and population connectivity of the two known populations and amongst sampling localities confirmed that connectivity and relatedness exist among the sampling sites, and that the northern and southern meta-populations are less well connected. Table Bay area was revealed unique because of its high relatedness. The sampling sites are different from each other in terms of population connectivity and relatedness, suggesting spatial partitioning in relation to environmental and social factors within the population, with some level of connectivity displayed in certain localities. The establishment of shark nets along the KwaZulu-Natal coastline that protects beach goers has had a long-term detrimental effect on the bottlenose dolphin (Tursiops aduncus) populations that inhabit the area since they are incidentally caught in these nets. A comparative study was done by comparing recently collected data (2007 - 2011) to previous sampling (1994 - 2000; Natoli et al. 2008) using mitochondrial DNA control region sequences (583 bp) and fourteen nuclear microsatellite data. The mtDNA sequences suggest that the coastal/migratory population has undergone a relatively recent demographic change shown by the FST value (ФST = 0.1138, P < 0.0180) in conjunction with the strong expansion signal shown by the mismatch distribution. It is suggested that the two populations be managed independently with a strong focus on conserving the coastal resident population North of Ifafa. Population Viability Analysis revealed that the coastal resident population of T. aduncus would be more affected than the migratory population by the number of individuals being caught in the shark nets. With respect to C. heavisidii, sensitivity analysis revealed that as little as 15 individuals removed from a small population size (n = 10 000) will produce a trend that may affect the overall population size of this species. This study exemplifies the importance of gathering long term life history data, inclusive of the threats faced by both species, in order to implement the correct conservation measures for continual monitoring to take place and ensure the survivorship of both species.