Colobines, a subfamily of Old World monkeys, is unique, in that its members eat mainly leaves, rather than fruits and insects.
It is known that some genes are generated through the duplication of other genes.
Through selective pressure, the duplicate gene may evolve, acquiring a different function to that of the original gene.
There are few examples, however, in which the evolution of a duplicated gene can be attributed to a particular selective pressure, and where it is known that its protein product has truly acquired a new functional activity.
Leaf-eating monkeys digest their food similarly to the way in which cows digest grasses.
| RNASE1B has enhanced ability to break down single-stranded RNA.
| Nature Genetics |
Bacteria in the gut break down the leaves, and in turn the monkeys digest the bacteria to recover nutrients.
Jianzhi Zhang, of the University of Michigan in Ann Arbor, USA, and colleagues from two other institutions, show that, in the douc langur (an Asian colobine), a duplicated copy of a gene encodes a pancreatic enzyme with an enhanced ability to break down single-stranded RNA.
RNAs from rapidly growing bacteria, like those found in the monkeys' gut, have high nitrogen content.
The authors speculate that the enzyme, called RNASE1B, breaks down bacterial RNA to release and allow the recovery of the nitrogen. They have also shown that the enzyme works more efficiently than the "parent" enzyme, at the pH of the douc langur's gut.
Fossil records show that colobines turned to leaf-eating and gut fermentation at least 10 million years ago, before the estimated time of the duplication.
This suggests that changes in diet and digestive "strategy" provided selective forces for a modified RNAse, and gene duplication provided the raw material.