28 May Paper on hybridization in the wild
Rocio Espada from WCA Partner Dolphin Adventure Gibraltar recently co-authored a paper on a case of hybridization in the wild between a female bottlenose dolphin and a short-beaked common dolphin in the Mediterranean.
The article entitled Hybridization in the wild between Tursiops truncatus (Monatgu 1821) and Delphinus delphis (Linnaeus 1758) was published in the online journal PLoS One in April 2019, and details the encounter of the hybrid dolphin in the Bay of Algeciras in southern Spain from August 2016 to June 2017.
Since 2006 a lone female bottlenose dolphin, known locally as Billie, has been observed with groups of common dolphins in the area. In August 2016 Billie was seen pushing a neonate to the surface, with no other dolphins around. Photographs taken before and after this date of Billie strongly indicate she had been pregnant and that the calf was hers. Billie’s history and apparent adoption by common dolphins in the area and the encounters recorded over the next 25 weeks led researchers to believe this was a hybrid. For the first 3 months of observation the female bottlenose dolphin was observed showing attentive care and nurturing behaviour towards the newborn, and the two were observed predominantly in the echelon swimming position (the calf swimming alongside the mother). In addition, nursing was recorded at least four times. This strongly suggested that the female bottlenose dolphin was the calf’s mother.
Photographs of the calf showed morphological characteristics of both common dolphin and bottlenose dolphins, with colouration and striping patterns of the calf, corresponding with markings characteristic of common dolphins all be it slightly muted. This indicated that the father was likely to be a common dolphin.
The decision was taken not to risk taking biopsy samples at this stage, with the team not wanting to risk the health of the calf. Sadly after June 2017 there were no further sightings of the hybrid calf and it is presumed to have died.
Despite the loss of the calf this case of hybridization provides significant and valuable information on hybridization in wild cetacean populations, not least between two vulnerable populations of cetaceans in an area heavily impacts by human activity.