258 — Whole-genome sequencing of the blue whale and other rorquals finds signatures for introgressive gene flow

Rorquals are the group of baleen whales that look like they were designed for swimming. They are also the largest animals on Earth. This is in contrast with other whales — including right whales or bowhead whales — which look like they were designed for minimizing hydrodynamics and maximizing inefficiency when swimming. (But I love them all anyway.)

ANYHOW. Whale evolution is poorly understood, because ① we kept killing them, and that’s bad, and ② they’re very large and marine, which makes it also hard to ask for their DNA. And even the evolutionary studies we have performed largely disagree with one another; many studies suggest that humpbacks and gray whales belong in their own phylogenetic genus based upon anatomy, but genetically appear to have evolved from the rorquals. (Wikipedia’s phylogenetic tree represents this with a resigned “…” where there should be a genus name.)

What makes this evolutionary lineage even more complicated is the fact that whales can, under certain conditions, hybridize. Rorqual hybrids can produce fertile offspring, which means that the evolutionary tree probably looks more like an evolutionary network.

This research looks at six baleen whales and one control — a hippopotamus. Hippopotamuses are not whales.

This genetic control allowed the researchers to determine which genes should be conserved across all whales, and which genes, when conserved, were instead evidence of a genetic crossover, hybridization event, or something else phylogenetically interesting.

The results suggest that baleen whale evolution is not a bifurcating tree, and so conventional tree-based models are inadequate to describe the evolutionary history. And this is strong evidence for sympatric speciation: In other words, the whale groups diverged evolutionarily even though they remained in the same general habitats as one another.