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article imageDNA reveals genetic differences in killer whales

By Igor I. Solar     Apr 23, 2010 in Science
La Jolla - A report published April 22 in the journal Genome Research provides genetic evidence supporting the concept that there may be several species of killer whales (Orcinus orca) roaming the world's oceans.
Phillip A. Morin, geneticist at NOAA's Southwest Fisheries Science Center in La Jolla, California, and lead author of the paper, had suspected for some time that there was more than one species of killer whale (Orcinus orca, a.k.a. orca). The report on Genome Research describes genetic analysis of mitochondria DNA (mDNA) of 139 individuals from various locations in the North Pacific, North Atlantic and southern oceans (Antarctic). The paper also establishes a method for more accurately assess the differences in phylogeography (historical processes that may explain the current geographic distributions of individuals) and the time of divergence of the genomes. Finally the research team recommends that three genetically distinct geographic varieties be elevated to the rank of full species, and that other types also identified in the study be recognized as subspecies pending additional data.
The killer whale is officially considered a single species; however the likelihood of the existence of several races, sub-species or even species has been a matter of debate among sea mammal scientists for some time. Until now the differences noted in behavior, feeding preferences and certain physical features on whales in various geographic locations throughout the world's oceans have been inconclusive to support the existence of different species.
Dr. Morin said:
"The genetic makeup of mitochondria in killer whales, like other cetaceans, changes very little over time, which makes it difficult to detect any differentiation in recently evolved species without looking at the entire genome,"
He further stated:
"But by using a relatively new method called, 'highly parallel sequencing' to map the entire genome of the cell's mitochondria from a worldwide sample of killer whales, we were able to see clear differences among the species."
Establishing the genetic differences between the various populations of killer whales and their taxonomical identity may help biologists to better understand their role in the marine ecosystem and ascertain conservation priorities.
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