How early mammals evolved night vision to avoid predators

Date: June 20, 2016

Source: Cell Press

Early mammals evolved in a burst during the Jurassic period, adapting a nocturnal lifestyle when dinosaurs were the dominant daytime predator. How these early mammals evolved night vision to find food and survive has been a mystery, but a new study publishing June 20 in Developmental Cell suggests that rods in the mammalian eye, extremely sensitive to light, developed from color-detecting cone cells during this time to give mammals an edge in low-light conditions.

Cone cells are specialized for certain wavelengths of light to help animals detect color, while rods can detect even a single photon and are specialized for low-light vision. "The majority of mammals have rod-dominant retinas, but if you look at fish, frogs, or birds, the vast majority are cone-dominated--so the evolutionary question has always been, 'What happened?'" says Anand Swaroop, a retina biologist at the National Eye Institute, part of the National Institutes of Health. "We've been working for a long time to understand the fundamental mechanisms behind rod and cone development."

Previous work done by Swaroop and his colleagues showed that a transcription factor called NRL pushes cells in the retina toward maturing into rods by suppressing genes involved in cone development. "We began to wonder if, somehow, the short-wavelength cones were converted into rods during evolution," says Swaroop.

To investigate the origin of rods in mammals, Swaroop and his team examined rod and cone cells taken from mice at different stages of development. Details of an organism's embryonic development often reveal traits carried by its evolutionary ancestors; consider, for instance, how human embryos initially develop gill-like slits and a tail.

Continued … 

Cat and Mouse: One Gene Is Necessary for Mice to Avoid Predators

Apr. 29, 2013 — When a mouse smells a cat, it instinctively avoids the feline or risks becoming dinner. How? A Northwestern University study involving olfactory receptors, which underlie the sense of smell, provides evidence that a single gene is necessary for the behavior.

A research team led by neurobiologist Thomas Bozza has shown that removing one olfactory receptor from mice can have a profound effect on their behavior. The gene, called TAAR4, encodes a receptor that responds to a chemical that is enriched in the urine of carnivores. While normal mice innately avoid the scent marks of predators, mice lacking the TAAR4 receptor do not. 

The study, published April 28 in the journal Nature, reveals something new about our sense of smell: individual genes matter. 

Unlike our sense of vision, much less is known about how sensory receptors contribute to the perception of smells. Color vision is generated by the cooperative action of three light-sensitive receptors found in sensory neurons in the eye. People with mutations in even one of these receptors experience color blindness. 

"It is easy to understand how each of the three color receptors is important and maintained during evolution," said Bozza, an author of the paper, "but the olfactory system is much more complex." 

In contrast to the three color receptors, humans have 380 olfactory receptor genes, while mice have more than 1,000. Common smells like the fragrance of coffee and perfumes typically activate many receptors.

More: http://www.sciencedaily.com/releases/2013/04/130429154115.htm