There are two distinct populations of gray whales in the Pacific. The eastern population lives along the coasts of California and Mexico, while the western population is found off the coast of Russia.

New research suggests the two populations aren't entirely distinct and occasionally interbreed.

The eastern population of gray whales is significantly larger than the western population. Population growth rates in the eastern Pacific consistently outpace population growth to the west.

"At any one time, there is a huge disparity in the number of whales in each location. Some think that intense Russian and Japanese commercial whaling in the 1950s might have wiped out the entire population in the west," Andrew DeWoody, a professor of biological sciences at Purdue University, said in a news release. "It's possible then that a few survived and have been increasing in population. Or some might have dispersed from the east to make up today's western population. It might also be a combination of the two."

To better understand the divergent populations, DeWoody and his colleagues conducted a genomic survey of the two populations. When scientists compared the genotypes of 77 western and 135 eastern gray whales, they found genetic differences comparable to the differences between distinct subspecies.

But while the findings, published this week in the journal Biology Letters, suggest the two populations have evolved separately for some time, they haven't lost contact.

Previous tracking studies have documented trans-Pacific treks by whales from each population, and the latest genomic analysis suggests there is still gene flow between the two populations -- meaning specimens from the two populations occasionally interbreed.

The findings also revealed a significant amount of genetic diversity within both populations, good news for the smaller, more vulnerable western population. Whales from California may be providing their Russian cousins with an influx of genetic diversity.

"If you have a tiny population, a critically endangered population as we see in the west, you want to maintain gene flow and make sure they don't lose genetic diversity," said Anna Brüniche-Olsen, a postdoctoral researcher at Purdue. "There seems to be gene flow between the two. It might be that even though it's different population, they're not completely separated."

The authors of the latest study think genomic analysis such as theirs can prove helpful to assessing the vulnerability -- or risk of extinction -- among different endangered species populations.

"As we've seen with gray whales, it's a lot more complicated than the number of animals in the west and the east," DeWoody said. "Using genetics is going to prove to be a better method for understanding the population structures of endangered species and how those might be affected by human pressures or by natural processes such as ocean currents."

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