Patterns of geographic variation between mitochondrial and nuclear markers in Heaviside's (Benguela) dolphins (Cephalorhynchus heavisidii).

The Heaviside's (or Benguela) dolphin (Cephalorhynchus heavisidii) is endemic to the west coast of southern Africa. The present study investigated the population genetic structure across a large portion of the species distribution using mitochondrial control region and nuclear (microsatellite) markers. A total of 395 biopsy skin samples were analyzed; they were collected from free-ranging Heaviside's dolphins in 7 locations along 1650 km of coast between Table Bay, South Africa and Walvis Bay, Namibia. Both genetic markers rejected the hypothesis of 1 homogenous population but revealed contrasting results in the genetic structuring of putative populations. Mitochondrial DNA suggested either 2 populations or a fine-scale division with 6 (sub) populations, while microsatellite markers were indicative of 2 widespread populations with measurable gene flow between them. Neutrality tests and mismatch distribution of the mitochondrial sequences indicated a departure from mutation-drift equilibrium due to a population expansion at the 2 extremes of the geographic range, but not towards the middle of the distribution. These results highlight the importance of evaluating multiple genetic markers to gain reliable insights into population processes and structure.