The evolution of killer whale behaviour and social structure is characterized by the expansion of a small number of pioneering groups into new environments, reports a study published this week in Nature Communications. The study, based on whole genome sequences from 50 killer whales, adds to our understanding of the population history of these animals.
Killer whales (Orcinus orca) - the largest species in the dolphin family - are highly social animals spanning a wide range of habitats, from Antarctic to Arctic regions. In several locations, killer whales have evolved into specialized groups known as ecotypes based on diet and hunting strategies adapted to exploit narrow ecological niches. However, the influence of genetic as opposed to ecological factors in behavioural and ecotype variation has been unclear until now.
Andrew Foote and colleagues sequenced the whole genomes of 50 individual killer whales from five different ecotypes from the North Pacific and Antarctic regions. They estimated that killer whale ecotypes have radiated globally in less than 200,000 years. The authors found that, in all studied ecotypes, a population decline after divergence was followed by an expansion, one of the major evolutionary scenarios that allows new subgroups to emerge. The genome data also reflected the evolution of killer whale social structure and hunting behaviour.
This study provides insights into how the evolution of social animals is influenced by the interaction of culture and genes.