Genes and Culture Drive Killer Whale Evolution

Killer whale moving quickly
This killer whale was encountered during a marine mammal survey conducted by NOAA's Southwest Fisheries Science Center. Photo credit: Isabel Beasley.

Killer whale behavior and social structure evolved through the expansion of a small number of pioneering groups into new environments, reports a genetics-based study published this week The previous link is a link to non-Federal government web site. Click to review NOAA Fisheries disclaimer in Nature Communications. The study seeks to unravel the population history of killer whales based on the newly sequenced genomes of 50 individuals.

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.

“Genome sequencing gives us new insight into the into the speciation process where culture and genetics interact,” said Phil Morin, a marine mammal geneticist at NOAA Fisheries’ Southwest Fisheries Science Center, and a coauthor of the new study. “In killer whales, social cohesion and learned hunting behavior (cultural innovation) appear to have reinforced isolation of small founding groups, resulting in rapid divergence and adaptation. Some of these ecotypes appear to be well on the way to being new species.”

For example, a recent study published in the journal Polar Biology found that killer whale types around the Antarctic Peninsula are diverging into a large seal-eating form and a smaller penguin-eating form. “We have observed dietary, behavioral and non-overlapping size differences between these forms - evidence for adaptation to distinct foraging niches,” said John Durban of the Southwest Fisheries Science Center and lead author of that study.

“The genomes of these two forms indicate that social cohesion and the cultural transmission of learned hunting behaviors appear to have reinforced their isolation, resulting in their rapid divergence,” said Durban, also a coauthor of the new study.

For the new study, Andrew Foote of Uppsala University in Sweden and  his 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 the killer whale’s social structure and hunting behavior.

This study provides insights into how the evolution of social animals — including humans — is influenced by the interaction of culture and genes.

“The origins of killer whale types are diverse and complex,” Morin said. “Genomic data show us the ancestral relationships, the changes in population size and genetic changes that accompanied the origins of each ecotype. These details help us understand where ecotypes are on the speciation continuum, which is important for understanding their evolution and for conservation of their diversity.”


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