Whales’ Gut Microbes

“You are what you eat,” is how the saying goes. And we often see that with the microbes in our guts. But it could also be said you are what your ancestors ate. According to a study published this week in Nature Communications, the gut microbes in baleen whales are determined as much by their ancestors as by their diets.

How do you study the gut microbiota of whales and other animals? Poop, of course! Researchers collected fresh fecal samples from several baleen whales in the Bay of Fundy in 2011. “It was a thrill to set out each morning into uncertain weather to search for elusive right whales, then to extract and sequence DNA from our smelly trophies,” says study co-author Annabelle Beichman of UC Los Angeles. “It had always been my passion to use the latest advances in genetic sequencing technology to answer questions about species of conservation concern, and so I wanted to add a genetic component to the study.” Beichman and her colleagues compared the DNA from whale feces to feces of other marine and terrestrial mammals.

The researchers were unsure what they might uncover in the poop. Baleen whales are meat eaters (they consume small crustaceans) but their closest living relatives are plant-eating cows, camels and hippopotamuses. “Given what we know about whales’ ancestry—that they’re related to ruminants, and that they still have a multi-chambered foregut—there were several things we might find,” explains lead author Peter Girguis of Harvard University and MBARI. “One hypothesis was that their microbiome would look like those of other meat-eaters like lions and tigers, and the foregut was just vestigial. The other hypothesis was that it allowed a different group of microbes to do something we hadn’t thought about. What we found was that whales have a microbiome that looks halfway like a ruminant and halfway like a carnivore.”

The team believes that this combination of dual microbial communities allows the whales to extract the most nutrition possible from their diet, digesting not only the crustaceans they eat, but their chitin-rich shells as well. The chitin—like the cellulose that cows eat in plants—is broken down in the fermentation chamber of the whale’s stomach. Given the size of whales, this combination seems incredibly efficient.

And whales aren’t the only ones with these odd gut microbes. The gut microbiota of bamboo-eating pandas is very similar to that of their close relatives—meat-eating bears. Both pandas and whales demonstrate that evolutionary history lives on, inside our guts!

Image: NOAA