The findings reported in Nature Commmunications September 22, 2015 support the notion that both diet and evolutionary history contribute to shape the microbial communities inhabiting the gut of mammals.
Diet is a major factor determining the composition of gut microbiota in mammals. Marine carnivores like whales evolved from plant-eating terrestrial ancestors related to cows and hippopotamuses.
Peter Girguis of Harvard University led the study, in which Bigelow Laboratory for Ocean Sciences David Emerson and Jarrod Scott participated. The researchers compared the microbial genes found in whale fecal samples with similar data obtained from other marine and terrestrial mammals with various diets. The scientists found that the gut microbiome of right whales and other baleen species share characteristics with both herbivore cows and meat-eating predators. Baleen whales’ overall microbiota composition and functional capacity resemble those of their terrestrial herbivore relatives, but certain microbial metabolic pathways were more similar to those of terrestrial carnivores.
“From one point of view, whales look like carnivores,” Girguis said.
“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.”
Added Emerson: ”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.”
Emerson and Scott at Bigelow Laboratory are exploring what these gut microbes can tell about the health and biology of Northern Right whales in the wild, where only a few hundred of these endangered animals remain. Emerson says, “This study opens the possibility of being able to track and investigate the microbiota of a wild animal population to understand more about the dynamics of their diet, and how this may impact their health. It is unprecedented.”
The study helps to clarify the complex roles of diet and evolution in determining the composition of microbiomes. The authors propose that, for baleen whales, the correlation between evolutionary relatedness and gut microbiota composition may reflect constraints imposed by the structure of the gastrointestinal tract. The whales and their terrestrial relatives possess a multi-chambered foregut that acts as a fermentation chamber.
In addition to Girguis, Emerson, and Scott, other co-authors of the paper are: James McCarthy, professor of Biological Oceanography, Alexander Agassiz, professor of Biological Oceanography in the Museum of Comparative Zoology, Jon Sanders, and Annabel Biechman, all from Harvard University, and Joe Roman from the University of Vermont.
