Researchers conducted a controlled lab experiment by implanting gut microbes from two large-brained primates (humans and squirrel monkeys) and one small-brained primate (macaques) into mice. The results showed mice with microbes from large-brained primates produced and used more energy, while mice with microbes from the smaller-brained macaque stored more energy as fat.
This research provides the first evidence that gut microbes influence biological differences between species and supports the theory that these microbes could have shaped evolution by altering how an animal's body generates and uses energy.
"We know the community of microbes living in the large intestine can produce compounds that affect aspects of human biology - for example, causing changes to metabolism that can lead to insulin resistance and weight gain," said Katherine Amato, associate professor of anthropology at Northwestern and the study's lead author.
Amato further explained, "Variation in the gut microbiota is an unexplored mechanism in which primate metabolism could facilitate different brain-energetic requirements."
The study expands on prior research that primarily focused on genetic and environmental influences on brain size. Few studies have explored how different primates use energy or the role of metabolism in brain evolution.
By measuring traits such as weight gain, fat percentage, liver function, and glucose levels, researchers observed significant physiological changes in the mice over time. Although they expected human-derived microbes to produce the most dramatic differences, the most significant patterns emerged between mice inoculated with microbes from large-brained (human and squirrel monkey) versus small-brained (macaque) primates.
"While we did see that human-inoculated mice had some differences, the strongest pattern was the difference between large-brained primates (humans and squirrel monkeys) and smaller-brained primates (macaques)," Amato said.
Interestingly, mice inoculated with microbes from humans and squirrel monkeys shared similar physiological traits despite the evolutionary distance between these two species. This suggests that the trait of having a large brain, rather than genetic relatedness, likely influenced the gut microbiome's role in energy production.
"These findings suggest that when humans and squirrel monkeys both separately evolved larger brains, their microbial communities changed in similar ways to help provide the necessary energy," Amato explained.
Future research will include experiments with microbes from additional primate species of varying brain sizes. Researchers also aim to identify more compounds produced by these microbes and examine their effects on host traits such as immune function and behavior.
Research Report:The primate gut microbiota contributes to interspecific differences in host metabolism
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