Published May 15, 2019
Starch, a complex carbohydrate, is a vital source of nutrition for many mammals. Humans farm it in the form of rice, wheat, corn, potatoes and oats. Rats comb our garbage piles for scraps of pizza and bread. Wild boars root for tubers.
Now, a new study is providing insight into how the pursuit of starch may have driven evolutionary adaptations in these and other hungry mammals.
The research, conducted on 46 mammal species, focuses on a biological compound called amylase, which is produced by humans and other animals to break down starch.
The study finds that in the course of mammalian evolution, the genetic machinery that teaches the body how to make amylase has been something of a chameleon. It has evolved in different ways in different beasts, and it’s capable of changing rapidly, possibly in accordance with what animals eat.
The study finds that mammals with starchy diets tend to have more copies of the amylase gene, which carries instructions for building amylase, than mammals that consume little starch (at least among the species studied).
The research also presents evidence that evolutionary changes related to amylase — including duplications of the amylase gene and the ability to produce amylase in saliva — may have arisen independently in some different species. Called convergent evolution, this phenomenon often signals a particularly useful adaptation.
Findings were published on May 14 in eLife. Overall, the study paints a colorful picture of the evolutionary history of amylase across mammals, ranging from humans, dogs and house cats to hedgehogs and ring-tailed lemurs, along with baboons that store food in their cheeks.
“Amylase is a case where diet may have the potential to change our genes. This is fascinating,” says Omer Gokcumen, assistant professor of biological sciences, College of Arts and Sciences. “The duplications we see in the amylase gene give a very flexible and rapid way in which gene functions can evolve, and this mechanism of evolution is underappreciated.”
“Past studies have explored the evolution of amylase in select species, such as humans and dogs, but our research takes a broader perspective,” says Stefan Ruhl, professor of oral biology in the School of Dental Medicine. “We examine dozens of mammalian species from different branches of the evolutionary tree, and we see that when it comes to amylase in saliva, genetics and biology may respond to what we eat.”
The study was led by Gokcumen, Ruhl and first author Petar Pajic, a UB oral biology and biological sciences researcher.
Details on the findings:
“This study provides the most comprehensive picture, to date, on how amylase has evolved in the mammalian lineage at both the genetic level and at the level of protein expression in saliva,” says Pajic, the study’s first author. “From a broader theoretical stance, it also reveals how quickly evolution can happen and how something simple, like the food you eat, may drive otherwise unrelated species to evolve similarly.”
For animals who don’t store food in their cheeks, the evolutionary advantage of having amylase in saliva is unclear. But Ruhl, a leading salivary researcher, says one theory is that it helps animals and humans identify starchy foods as desirable to eat.
“Humans have a lot of salivary amylase, but why?” he says. “Unlike the baboons who predigest food in their cheek pouches, we humans do not keep food in our mouths long enough for any substantial digestion to happen. One idea is that salivary amylase evolved to help our ancestors detect starch. They would not be able to taste it otherwise. Amylase liberates sugar in starch, and this may help animals develop a taste preference for starch-rich foods like potatoes or corn.”
Other hypothesized purposes for salivary amylase include cleaning sticky starch residues from teeth. “Amylase in saliva might act as a kind of biochemical toothbrush nature has provided us with,” Ruhl says with a smile. “It could help to regulate the makeup of the oral microbiome.”
The research — supported by the National Institute of Dental and Craniofacial Research, National Cancer Institute and National Science Foundation — included researchers from UB, the Foundation for Research and Technology in Greece, SUNY Plattsburgh, Cornell University and the Friedrich-Loeffler-Institut in Germany.