331 — Genome-culture coevolution promotes rapid divergence of killer whale ecotypes

Something that I didn’t know about killer whales: The evolution of killer whales is extremely recent, and they probably “globally radiated within less than 250,000 years.” This means that Homo sapiens remembers a time before killer whales existed. Wow.

Orcas — which are in the dolphin family, another thing that I didn’t know until today — have in some cases adapted to extremely niche ecological positions. This isn’t of course surprising: Humans have done almost exactly the same things. (Take, for example, populations which, over thousands of years, have adapted to live in oxygen-deprived regions like the Andes, or perhaps have adapted to live in extreme cold in the arctic.) Much like sperm whales (see yesterday’s paper), orca society is matrilineal, and due to the long post-menopausal lifespan of a killer whale, we can assume that teaching younger generations hunting or survival technique is a core component of the orca life.

One of the questions that we have about orcas is why they so quickly spread across the planet, and how they so quickly adapted to the wide variety of ecosystems. Some orcas, for example, eat penguins; others eat larger mammals. And others still feed on almost only fish. Generally speaking, these diets are pretty strict, and an orca of one ecotype doesn’t stray into the others’ diets.

To answer this question (among many others), the authors sequenced the genomes of a handful of orcas from a selection of these ecotypes. From this, they were able to establish a most-likely evolutionary pathway for each ecotype to arise — although as I have mentioned previously, whale evolutionary lineages are pretty convoluted.

The results suggest that orca ecotypes likely separated both as a result of natural selection pressures as well as the intentional, directed, social knowledge transfer common to all social mammals.