Rare Breed of Killer Whale May Be New Species.

In class, we get lots of definitions for a species, including:

• the phenetic species concept
• the phylogenetic species concept
• the evolutionary species definition
• the biological species definition

In my class and most of biology, we tend to stick with the biological species concept, which requires that individuals be able to interbreed and produce viable, fertile offspring.  This definition has the advantage of being relatively easy to employ for a lot of living critters that mate sexually.  However, it does not work well for asexually reproducing species (for example, bacteria that undergo fission) or for haplobiontic organisms, since they do not require mating.  It also means that realistically, Chihuahuas and Great Danes should be classified as separate species, since they do not mate with each other under normal circumstances (due to size differences); French bulldogs are reportedly incapable of mating naturally as well.  Do they constitute separate species?

This makes me wonder what basis was chosen for assigning these killer whales the moniker of “new species.”  Based on the National Geographic article, the quick answer is DNA evidence. The researchers used mitochondrial DNA (inherited solely from the mother) and looked for the number of genetic differences between this subtype of whale and other killer whales.  Some differences were expected: the body shapes and color patterns are slightly different.

I got really, really curious, so I went and got the full article from Polar Biology vol iss pp 1-5 (entitled Mitogenomic insights into a recently described and rarely observed killer whale morphotype; available free to ODU students).  They compared the DNA of 140 whale samples.  What they found was surprising: these killer whales… weren’t like other killer whales.  Okay, so that’s obvious from the title, but they were genetically more different than expected.  Based on mutation rates, the last common ancestor for this whale and other whale species lived around 390,000 years ago.  That’s actually fairly recent.  They were most closely related to a group of mammal-eating, North Pacific “transient” whales.  Neat!  I don’t know enough about whales to know what that means.

The authors were pretty forthright about the issue of species definition:

“Whilst mitogenomes [mitochondrial DNA genomes] from more samples and nuclear DNA analysis are required to confirm that type D is reproductively isolated from other killer whale types to qualify as a new species under the Biological Species Concept, in the absence of this data, the deep divergence within the killer whale phylogeny, divergent morphology, and, apparently, overlapping at-sea range with all of the other Southern Ocean types provide accumulating lines of evidence that suggest type D is potentially a new species or subspecies of killer whale (see De Queiroz 2007; Morin et al. 2010).”