Thursday, June 2, 2016

[Cetacea • 2016] Genome-Culture Coevolution promotes Rapid Divergence of Killer Whale Ecotypes

Figure 1: Map of sampling locations of the five killer whale types included in this study.
Map of sampling locations of the five killer whale types included in this study. Sampling locations and inset photographs illustrating favoured prey species are colour-coded by ecotype: ‘transient’ (blue) and type B1 (purple) are predominantly mammal-eating; ‘resident’ (brown) and type C (orange) are predominantly fish-eating; type B2 (green) is known to feed on penguins. The map is superimposed on a colour grid of sea-surface temperature (SST). The Antarctic ecotypes primarily inhabit waters 8–16 °C colder than the North Pacific ecotypes. The relationship among these types and their estimated divergence times based on mitochondrial genomes are shown in the superimposed chronogram. Boxes 1–4 indicate pairwise comparisons spanning points along the ‘speciation continuum’ used to investigate the build up of genomic differentiation.

Analysing population genomic data from killer whale ecotypes, which we estimate have globally radiated within less than 250,000 years, we show that genetic structuring including the segregation of potentially functional alleles is associated with socially inherited ecological niche. Reconstruction of ancestral demographic history revealed bottlenecks during founder events, likely promoting ecological divergence and genetic drift resulting in a wide range of genome-wide differentiation between pairs of allopatric and sympatric ecotypes. Functional enrichment analyses provided evidence for regional genomic divergence associated with habitat, dietary preferences and post-zygotic reproductive isolation. Our findings are consistent with expansion of small founder groups into novel niches by an initial plastic behavioural response, perpetuated by social learning imposing an altered natural selection regime. The study constitutes an important step towards an understanding of the complex interaction between demographic history, culture, ecological adaptation and evolution at the genomic level.

Andrew D. Foote, Nagarjun Vijay, María C. Ávila-Arcos, Robin W. Baird, John W. Durban, Matteo Fumagalli, Richard A. Gibbs, M. Bradley Hanson, Thorfinn S. Korneliussen, Michael D. Martin, Kelly M. Robertson, Vitor C. Sousa, Filipe G. Vieira, Tomáš Vinař, Paul Wade, Kim C. Worley, Laurent Excoffier, Phillip A. Morin, M. Thomas P. Gilbert and Jochen B.W. Wolf. 2016. Genome-Culture Coevolution promotes Rapid Divergence of Killer Whale Ecotypes. Nature Communications. 7, Article number: 11693.
DOI:  10.1038/ncomms11693

Orcas are first non-humans whose evolution is driven by culture