Whales and Poop: Whales Are Like Both Cows and Predators Where It Counts

In another chapter of the continuing story of how important large animals' poop is to the Earth, scientists recently analyzed the fecal matter of 12 baleen whales from three different species. They found that whales with baleen are an intriguing combination of species, gut-wise--they feed on crustaceans and fish, and are therefore carnivores, but their guts contain microbes (their whale microbiome) similar in some ways to those inside herbivore cows and meat-eating predators, according to a release.

This is not without precedent: Marine carnivores such as whales have plant-eating, land-dwelling ancestors with factors in common with hippopotamuses and cows. The team recently published their results detailing the poop discoveries and other points in the journal Nature Communications. They are from Harvard University, University of Vermont, and Bigelow Laboratory for Ocean Sciences (Maine). 

In the study, the scientists compared the genes of microbes found in whale poop with data from other water-based and terrestrial mammals having a variety of diets. While the composition of microbiota (the colonies of all microbes within a body) and how they function both are very much like those of terrestrial herbivores, certain pathways of microbial metabolism were more like those of carnivores that live on land, the release noted.

"From one point of view, whales look like carnivores," lead author Peter Girguis, of Harvard, said in the release. "They have the same kind of microbes that we find in lions and tigers that have very meat-rich diets. But they also have abundant communities of anaerobic bacteria, similar to those that ruminants use to break down cellulose. What we found was that whales have a microbiome that looks halfway like a ruminant and halfway like a carnivore."

The team had explanations for these combinations, too: David Emerson of Bigelow added in the release, "Such dual microbial communities allow whales to extract the most nutrition possible from their diet, digesting not only the copepods they eat, but their vegetable-like chitin-rich shells, as well."

Considering that only a few hundred Northern Right whales still exist in the wild, Emerson and Jarrod Scott at Bigelow are studying what the microbes can indicate about that whale's health and biology, a release noted.

The study also proposes that in baleen whales, evolutionary relatedness and the composition of gut microbiota might have to do with the limitations of the gastrointestinal tract. Both whales and land-dwelling relatives such as cows have a foregut with multiple chambers in which fermentation takes place, noted the release.

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