Molecular and Morphological Differentiation of Common Dolphins (Delphinus sp.) in the Southwestern Atlantic: Testing the Two Species Hypothesis in Sympatry

In this study we investigated the molecular taxonomy of common dolphins through analyses of cytochrome b sequences of 297 individuals from most of their distribution

Haydée A. Cunha; Rocio Loizaga de Castro; Eduardo R. Secchi; Enrique A. Crespo; José Lailson-Brito; Alexandre F. Azevedo; Cristiano Lazoski; Antonio M. Solé-Cava

2015

Scholarcy highlights

  • Delphinus delphis Linnaeus, 1758 is the earliest dolphin species described that is still valid today
  • The most obvious one is the existence of a single Delphinus species in the Atlantic, as individuals morphologically assigned to D. capensis based on rostral length/zygomatic width ratios do not differ genetically from shortbeaked individuals from several localities in the South and North Atlantic
  • Once the distinction of the two species in California was established both by good morphometric and genetic works, and the synonymy of D. bairdii and D. capensis had been wrongly proposed by van Bree & Purves, D. delphis and D. capensis became the two accepted species in the genus, with the RL/ZW ratio as the sole diagnostic character between them. This was used by researchers to identify common dolphins worldwide, even when genetic data consistently indicated that short-beaked and long-beaked common dolphins from the Atlantic did not form reciprocally monophyletic groups. Even though the latter authors did not draw any taxonomic conclusions on their work, which was based on both nuclear and mitochondrial markers, they hint at the possible non validity of D. capensis, stating that “the presently recognized long-beaked common dolphin species may prove to be invalid”, but at the same time that “it seems unlikely, despite their close genetic relationship, that all ecologically and morphologically distinct Delphinus populations belong to the same species”
  • We tested the two species hypothesis by assigning sympatric SW Atlantic specimens of differing morphotypes to either Delphinus species according to the rostral index of Heyning & Perrin
  • previous research, and verifying if they corresponded to D. delphis or D. capensis using the cytochrome b gene, as outlined by Rosel et al
  • We suggest that the name D. bairdii Dall, 1873 be used for long-beaked common dolphins restricted to the NE Pacific until further, more comprehensive analyses can be conducted

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