by Joe Caspermeyer

Brian Verrelli is on a quest. He wants to gain a more complete picture of the evolution of color vision. That quest led the Arizona State University molecular biologist to an up-close, genetic encounter with the aye-aye, one of the world’s most rare and bizarre-looking primates. (Click here for pictures and sounds.)

Verrelli is an assistant professor at ASU’s School of Life Sciences. He does research as part of the Center for Evolutionary Functional Genomics at the Biodesign Institute. He and his team performed the first sweeping study of color vision in the aye-aye (pronounced “eye-eye”).

The aye-aye is a bushy-tailed primate native to Madagascar. The creature has a unique combination of physical features including extremely large eyes and ears. Aye-ayes also have elongated fingers for reaching hard-to-reach insects and other foods.

Verrelli and his colleagues reached some surprising conclusions on how this nocturnal primate may have retained color vision function. The group is focused on color vision to better understand genetic variation between human and other primate populations. They also look at the truly big evolutionary questions. The biggest: What makes us human?

“At least within humans and some other primates, we know that there are three different genes responsible for color vision,” Verrelli says. The genes are called opsins. Opsins come in three forms that shape our color vision palette. There is an opsin for blue, another for green, and a third for red.

“The green and red opsins are found on the X chromosome [sex chromosome],” Verrelli explains. “It is the manipulation of those two genes alone which is related to color blindness for eight to 10 percent of the male population.”

Results of previous studies suggest that natural genetic selection has provided women with a frequent ability to better discriminate between colors than men.

“These three genes may explain all the variation that we might see across human populations in color vision,” Verrelli adds. But how did our range of color vision variation come to be in the first place?

To help trace back the evolution of color vision, Verrelli’s collaborator George Perry turned to the endangered aye-aye, a primate representative of lemurs.

Scientists believe that lemurs split from other groups including humans, apes, and monkeys more than 60 million years ago. They are thought to be in some ways representative of the early primates that lived at that time.

“We chose the aye-aye specifically because it has very interesting behavior,” Verrelli explains. “The animal is fully nocturnal. That raises an obvious and straightforward question: If you are an animal that lives at night, do you need color vision?”

In a simple case of “use it or lose it,” the prevailing theory suggested that nocturnal primates cannot use color vision to see. As a result, the genes they have for color vision accumulated mutations and degraded over evolutionary time.

From a practical standpoint, studying color vision in the aye-aye proved to be a daunting endeavor. The aye-aye is an endangered species. So collecting DNA samples in the wild was not possible. To get DNA samples for their study, the ASU group turned to a few rare international research institutions and colleagues that have aye-ayes.

In total, they were able to collect samples from eight aye-ayes. It then took a year and a half to analyze the samples. Perry and Verrelli had to invent the methodology to perform the first wide-range genetic analysis on the aye-aye.

“From a conservation, population, and functional viewpoint, it was the first study of its kind,” says Verrelli.

The results were startling. Verrelli says his team had to recheck them twice.

“When examining these genes in the aye-aye, we realized that they are not degrading,” he says. “In fact, for the green opsin gene, we did not find a single mutation. The opsin genes look to be absolutely fully functional. That is completely counter to how we had believed color vision evolved in nocturnal mammals.”

The results are important to understanding the evolution of color vision, Verrelli adds. They also show the value of examining the dazzling diversity of life, especially in endangered species.

The research was published in the journal Molecular Biology and Evolution. Go to http://mbe.oxfordjournals.org/cgi/content/full/24/9/1963 to see the full text. For more information about this and other research at ASU’s Biodesign Institute, visit http://biodesign.asu.edu