Scientists led by Dr Thomas Gilbert from the University of Copenhagen have used DNA from a museum specimen collected in 1955 to study what may be a distinct subspecies or species of killer whale (Orcinus orca).
One of seven currently known records of killer whales Orcinus orca type D: near the Crozet Islands, a sub-antarctic archipelago in the southern Indian Ocean (P. Tixier via Robert L. Pitman et al., 2011)
In 1955, a pod of unusual-looking killer whales stranded on a New Zealand beach and a skeleton was saved in a museum in Wellington. Photographs were also taken but it was almost 50 years before this unique form of killer whale, characterized by a very small white eye-patch and bulbous forehead, was documented alive in the wild.
Marine scientists have suspected for some time that there might be more than one type of killer whale, a theory supported by recent genetic studies. The so-called ‘type D’ killer whale from New Zealand, however, was not included in previous genetic studies because no tissue samples were available.
For the current study reported in the journal Polar Biology, the scientists extracted DNA from dried tissue and tooth fragments from the New Zealand skeleton, the only known specimen of type D killer whale.
Types of killer whale. The type D killer whale is immediately recognizable by its extremely small white eye patch, shorter than usual dorsal fin, and bulbous head (Albino Orca / CC BY-SA 3.0)
A complete mitochondrial DNA sequence of the type D specimen was compared to samples of 139 killer whales from around the world.
From that, the researchers estimated that type D separated from other killer whales approximately 390,000 years ago, making it the second oldest branch in the killer whale family tree and possibly a separate subspecies or species.
“Dramatic changes in global sea level and ice sheet coverage during the Pleistocene may have contributed to the diversification of killer whales.”
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Bibliographic information: Andrew D. Foote et al. Mitogenomic insights into a recently described and rarely observed killer whale morphotype. Polar Biology, published online June, 2013; doi: 10.1007/s00300-013-1354-0
