Clymene Dolphin Documented at First Hybrid Marine Mammal Species

The clymene dolphin, a small, sleek cetacean that lives in the Atlantic Ocean, came to be through a natural hybridization between to closely related dolphin species, according to marine biologists, who report the event as the first natural hybrid species documented among marine mammals.

Hybridization - where reproduction between two distinct species resulsts in offspring - is relatively common among plants, fish and birds, but is rare in mammals, the researchers report.

"Our study represents the first such documented instance of a marine mammal species originating through the hybridization of two other species," said lead study author Ana R. Amaral, a research associate at the American Museum of Natural History. "This also provides us with an excellent opportunity to better understand the mechanisms of evolution."

Until the 1980s, clymene dolphins were considered a sub-species of the spinner dolphin. But it was later established as a distinct species. The current study, published in the journal PLOS One, seeks to clarify outstanding questions regarding how the clymene dolphin came to be.

A genetic analysis revealed that the clymene dolphin is the hybrid of spinner and striped dolphins.

The researchers conducted the genetic analysis by sampling nuclear and mitochondrial DNA from skin samples obtained from both wild and deceased dolphins. Seventy-two samples were taken from clymene, spinner and striped dolphins. Biopsy darts were used to collect material from live, free-ranging dolphins, and samples were taken from deceased dolphins washed up in stranding events.

In the lab, the researchers were able to amplify one mitochondrial DNA marker and six nuclear DNA markers as a means of analyzing the evolutionary relationship between the dolphin species. The analysis revealed a measurable discordance among the nuclear and mitochondrial markers, which the researchers say is best explained by hybridization. The clymene dolphin's mitochondrial gene more closely resembled the striped dolphin, while its nuclear genome was more similar to the spinner dolphin.

"With its similar physical appearance to the most closely related species, our genetic results now provide the key insights into this species origin" said senior study author Howard Rosenbaum, Director for Wildlife Conservation Society's Ocean Giants Program. "Very little is known about the clymene dolphin, whose scientific name translated from Greek is oceanid, but ironically also can mean fame or notoriety. Hopefully, our work will help draw greater attention to these dolphins in large parts of their range."