Killer whales, like people, are widely dispersed from the tropics to the poles. But many populations seem to remain in a single area where they have carved out a specialised niche, hunting a particular target through a sophisticated hunting strategy. Some eat fish by herding them into bait balls, for instance, whereas others target mammals such as seals by deliberately stranding themselves on beaches where the seals live. Foote and his colleagues looked at the genomes of 50 killer whales from five niches – two in the Pacific Ocean and three in the Antarctic Ocean.
The genomes fell into five distinct groups that exactly mirrored the five cultural niches. The genomes indicate that all five groups began when a small founding population – numbering perhaps a few tens or hundreds of individuals – invaded each new niche and then expanded. Whenever a species passes through this sort of population bottleneck, it can rapidly gain a unique genetic identity.“One of the main conclusions is that variation within killer whales, humans and likely many other species arises from multiple interacting processes rather than being attributed to just culture, ecology or genetics,” says Foote.