Evidence of introgressive hybridization between Stenella coeruleoalba and Delphinus delphis in the Greek Seas

Abstract Natural interspecific hybridizationmight be more important for the evolutionary history and speciation of animals than previously thought, considering several demographic and life history traits as well as habitat disturbance as factors that promote it. In this aspect, cetaceans comprise an interesting case in which the occurrence of sympatric species in mixed associations provides excellent opportunities for interspecific sexual interaction and the potential for hybridization. Here, we present evidence of natural hybridizationfor two cetacean species commonly occurring in the Greek Seas ( Stenella coeruleoalbaand Delphinus delphis), which naturally overlap in the Gulf of Corinth by analyzing highly resolving microsatellite DNA markers and mitochondrial DNA sequences in skin samples from 45 individuals of S. coeruleoalba , 12 D. delphisand three intermediate morphs. Employing several phylogenetic and population genetic approaches, we found 15 individuals that are potential hybridsincluding the three intermediate morphs, verifying the occurrence of natural hybridizationbetween species of different genera. Their hybridsare fertile and able to reproduce not only with the other hybridsbut also with each of the two-parental species. However, current evidence does not allow firm conclusions whether hybridizationmight constitute a step towards the generation of a new species and/or the swan song of an already existing species ( i.e ., D. delphis). Given that the focal species form mixed pods in several areas of Mediterranean, this study is an excellent opportunity to understand the mechanisms leading to hybridizationin the context of gene flow and urges for the evaluation of the genetic status of common dolphinsin the Mediterranean.