“Eye” wonder

Last year I wrote about the possible basis for the many variations of eye color in birds (click here to read that post).  Unlike most mammals which sport a limited variety of pale blue, gray, green, to dark brown shades, I’ve noticed that frogs and toads, like birds, also exhibit a rich variety of eye colors.  And so, “eye” wonder why?

Leopard frogs have a golden-colored iris with some dark speckles running through it.

Similarly, Gray Treefrogs also exhibit that golden-colored iris with the darks streaks running through it.

But these highly colorful eyes are tame, compared to those of a couple of South American frogs.

Those are some mesmerizing eyeballs in this Ghost Glass Frog. Glass frogs have see-through skin, especially on their ventral surface, which is as transparent as glass permitting a view of their internal organs.  Are those wild purple lines etched on the silver background of its iris to captivate female glass frogs, or frighten potential predators?

Red-eyed Treefrogs sit quietly on the underside of leaves during the day. But if disturbed by a predator or nosy human, they flash their big red eyes, orange toes, and yellow and purple legs to startle and gain time to escape.  [Photo from Wikipedia, By Carey James Balboa via Wikimedia Commons]

The variety of eye color in frogs and toads is astounding, as captured in this collage by Jodi Rowley.

Just a sampling of the normal variation among amphibian species… From RealScientists.org

Surely all this ocular advertisement has purpose — beyond frightening would-be predators?  Any speculation from you, dear readers?

In addition to the flash of color provided by the wide-open frog eye, you may have noticed that frogs have the ability to project their eyes outward from their head, or retract the eyes inward level with their skull.

This leopard frog has staked out a calling site, hoping to attract females. But it’s broad daylight and he needs to be able to see approaching predators (and photographers). 

Extrinsic eye muscles that elevate the eye above the level of the head actually give the frog a 360 degree view of its environment.  Movement of the eyes downward presses on the roof of the frog’s mouth, helping to propel food down the back of the throat toward the stomach.  Eyes — the multiple use organ!