Study

Genome-culture coevolution promotes rapid divergence of killer whale ecotypes

Foote, Andrew D.; Vijay, Nagarjun; Ávila-Arcos, María C.; Baird, Robin W.; Durban, John W.; Wolf, Jochen B. W.

Nature Communications, 2016

Peer-reviewedgenomic studywild

What they did

Fifty killer whale genomes from five ecotypes across the Pacific and Antarctic were sequenced and analysed for population structure, divergence times and signals of selection.

Studied in: Orcinus orca
Sample size: 50 killer whale genomes sequenced across five ecotypes

The ecotypes diverged very recently — on the order of a few hundred thousand years, some far less — with little gene flow between them despite overlapping ranges. Regions under selection include genes associated with diet and digestion.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Learned foraging traditions restrict gene flow between ecotypes and are followed by genetic adaptation to those diets, a case of culture driving genomic divergence.

How NatureHQ reads it

This is the strongest version of the culture argument, and it should be read carefully. Genomic divergence between ecotypes is measured; that culture caused it is an inference from the correlation between behavioural and genetic boundaries. The direction is hard to establish and the authors say so. What is not in doubt is that populations sharing the same water, capable of interbreeding, are not doing so — and the thing separating them is what they eat and how they hunt.

Limitations

Causal direction between cultural and genetic divergence cannot be established from genomes alone.
Fifty individuals across five ecotypes is thin for population genomics.
Ecotype sampling is uneven, with North Pacific residents best represented.