Genetic Differentiation among Recently Diverged Delphinid Taxa Determined Using AFLP Markers

In the mid-1990s, a new common dolphin species (Delphinus capensis) was defined in the northeast Pacific using morphological characters and mitochondrial DNA (mtDNA) sequences. This species is sympatric with a second species, Delphinus delphis; morphological differences between the two are slight and it is clear they are closely related. Does the phenotypic distinction result from only a few important genes or from large differences between their nuclear genomes? We used amplified fragment length polymorphism (AFLP) markers to broadly survey the nuclear genomes of these two species to examine the levels of nuclear divergence and genetic diversity between them. Furthermore, to create an evolutionary context in which to compare the level of interspecific divergence found between the two Delphinus taxa, we also examined two distinct morphotypes of the bottlenose dolphin (Tursiops truncatus). A nonmetric multidimensional scaling analysis clearly differentiated both Delphinus species, indicating that significant nuclear genetic differentiation has arisen between the species despite their morphological similarity. However, the AFLP data indicated that the two T. truncatus morphotypes exhibit greater divergence than D. capensis and D. delphis, suggesting that they too should be considered different species.