DNA Discovery Reveals Surprising Dolphin Origins

Charles Q. Choi

A well-known dolphin species, the clymene dolphin, arose from mating between two separate and distinct dolphin species, report genetics researchers.

Also known as the "short-snouted spinner dolphin," the clymene dolphin (Stenella clymene) grows to nearly seven feet (2.1 meters) long and dwells in deep waters in tropical and temperate parts of the Atlantic Ocean.

Evolutionary biologists have seen other such hybrid species elsewhere in the animal kingdom. The new discovery, reported in the journal PLOS ONE by a team led by marine biologist Ana Amaral of Portugal's University of Lisbon, adds to increasing evidence of such cross-breeding commonly leading to new species, even in the wide-open oceans.

Clymene dolphins feed mostly at night when squid and fish come to the surface of the water. The short-snouted dolphin gets its name from the ocean nymph Clymene of Greek mythology. (See "Dolphins Have 'Names,' Respond When Called.")

Researchers initially thought the clymene dolphin was a subspecies of the spinner dolphin (Stenella longirostris). However, in 1981, a closer look at the clymene's anatomy revealed it was a distinct species.

But experts remained uncertain about the clymene's relationship with its close relatives. Although its outward appearance and behavior are more similar to those of the spinner dolphin, its skull features closely resemble those of the striped dolphin (Stenella coeruleoalba).

DNA Analysis

To help solve this mystery, the study scientists analyzed skin samples from 15 clymene dolphins, as well as from 21 spinner and 36 striped dolphins. They collected the DNA from free-ranging dolphinsusing special tissue-collecting dartsand from dead, stranded dolphins.

The investigators looked at nuclear DNA, which is found in the cell's nucleus and comes from both the mother and father, as well as DNA from their mitochondriathe cell's powerhousewhich possesses its own genes and is passed down solely from the mother.

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DNA Discovery Reveals Surprising Dolphin Origins