Disruptive Patterns & the Artist-Scientist

Many animals display disruptive coloration, a pattern that visually breaks up the edge of their shape. For example, Mabee’s Salamander (Ambystoma mabeei) wears speckles like frost along its side. And it was an artist who first described this biological phenomenon – Abbott Thayer. (1) His studies of these patterns influenced the use of camouflage in the military.

In a recent fun study, researchers placed graphic squiggle-snakes on a mock-leaf background or plain background. They manipulated the coloration – solid, patterned, or patterned with bold and bright edges to the shapes. The edge-enhancement made the squiggle-snakes more difficult to spot on a leafy background. It also confused the observer about the shape of the snake when it was on a plain background.

1. Behrens RR. 2008. Revisiting Abbott Thayer: non-scientific reflections about camouflage in art, war and zoology. Philosophical Transactions of The Royal Society 364(1516) 497-501
2. Sharman RJ and PG Lovell. 2019. Edge-enhanced disruptive camouflage impairs shape discrimination. i-Perception 10(5) 1-9

Fight, Flight, or FREEZE

When a predator approaches, options are limited – especially if you’re a tadpole. The woodfrog tadpole (Rana sylvatica) is known to stop swimming and sink to the pond bottom, an action called “freezing behavior.”

In one study, researchers exposed woodfrog embryos to some water from a predator’s tank with or without an injured tadpole (1). When the embryos hatched, the ones that had smelled both the predator and injured relative showed very reduced activity (freezing behavior) if re-exposed to just predator-water.

In mice, freezing behavior is affected by the size and speed of an object. Video showing lab mice exposed to various dots indicates that small, slow objects trigger mice to freeze. When exposed to terrifying large dots, mice take off.

1. Mathis, A., M.C.O. Ferrari, N. Windel, F. Messier, and D.P. Chivers. 2008. Learning by embryos and the ghost of predation future. Proc Biol Sci. 275(1651): 2603-2607.

 

Ring species (#Inktober2019 has begun)

A ring species includes a series of populations set around a large barrier. Each population is a little different from its neighbors, but those differences add up as the distance increases. So, as the populations meet each other on the other side of the barrier, they’ve built up so many differences that they no longer breed. It’s a wonderful example of evolution (parapatric speciation, if you’re interested).

This cutie is the Ensatina salamander which surrounds the San Joaquin valley of California.

Warts & All

Double, double, toil and trouble;
Fire, burn; and cauldron, bubble.

Shakespeare’s witches open Macbeth by tossing a toad into their cauldron, along with parts of snakes, newts, bats and other dejected, unfortunate creatures. Why such a bad rap? After all, people LOVE frogs – they turn into princes, they have good tasting legs, and some cultures consider them lucky. But toads? Feared, reviled. What’s the big difference?

Toads tend to live in drier environments than frogs. In the frog’s aquatic environment, escape is just a hop away. For toads, though, warts are the key to survival. The two large “warts” on a toad, just behind the head, are glands that secrete a substance toxic to the toad’s predators.

Ay, there’s the rub – Toads are associated with poison. They actually produce three kinds of toxins: two affect the heart and one can produce hallucinations. Some cultures have used these chemicals for medical purposes. Perhaps those Shakespearean hags were just brewing up a treatment for edema.

Protect toads! While the American Toad is not threatened or endangered, many other populations of amphibians are experiencing sharp declines.

Learn more about the American Toad (Bufo americanus) and hear it call at http://www.herpsofnc.org/herps_of_NC/anurans/Bufame/Buf_ame.html