Blue Whales Carry Surprising Levels of Another Species' DNA

The blue whale population has started to recover from the devastation brought by commercial whaling in the early 20th century. But the world's largest ever animal isn't quite the same. In analyzing the genomes of Balaenoptera musculus musculus—the "most endangered" of four subspecies of blue whale, per Indy100—researchers have found new evidence of interbreeding, which could pose a risk to the blue whale's recovery. Scientists have known for years that blue whales mate with fin whales, resulting in hybrid offspring known as flue whales. Unusually, flue whales can successfully reproduce with blue whales, resulting in what's known as "backcrossed" offspring, "with mostly blue whale DNA and some fin whale DNA," Live Science reports.

This was generally viewed as a rare phenomenon. But in analyzing the full or partial genomes of 31 B. musculus musculus whales, researchers discovered it was more common than anyone realized, at least in the North Atlantic. When backcrossed offspring reproduce with a parental species over time, DNA from one species is transferring into the genome of the other in a process known as introgression. "The amount of introgression between the species that we found was unexpected and much higher than reported previously," University of Toronto ecological geneticist Mark Engstrom, co-author of a study published last month in Conservation Genetics, tells Live Science. As the outlet notes, "around 3.5% of the group's DNA came from fin whales on average."

As there's no evidence of fin whales inheriting blue whale DNA, it's believed blue whales alone are able or willing to reproduce with backcrossed offspring. "We don't know why introgression appears unidirectional," but it could be that there are fewer blue whales than fin whales, limiting potential mating partners, Engstrom tells Live Science. Though gene flow can benefit species, experts fear reducing the amount of blue whale DNA across the population could make the whales less resilient to change. On the bright side, the genomes revealed there is significant gene flow between blue whales in the North Atlantic and those from the western Atlantic, resulting in a more genetically diverse and resilient population than expected. (More blue whale stories.)