Cited research: Genome Res. doi:10.1101/gr.102954.109 (2010)

Killer whales consist of several species, not just one, according to a genetic study.

Different populations or 'ecotypes' of killer whale (Orcinus orca) vary in traits such as body size, social structure and preferred prey. Yet analyses of fragments of their mitochondrial DNA — which is inherited only from the mother and is often studied to delineate species — have revealed very low levels of genetic diversity between ecotypes, probably because of low mutation rates.

Phillip Morin of the National Marine Fisheries Service in La Jolla, California, and his colleagues examined the entire mitochondrial genome of 139 whales from the North Pacific, North Atlantic and Southern oceans. The authors found enough genetic variation to suggest renaming three of the ecotypes as separate species and classifying the rest as subspecies until more data become available. L.O.-S.