There Be Dragons!

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Australian Water Dragons (Intellagama lasueurii) lounge and bask around pond edges at the University of Queensland, where I saw this handsome fellow. The colorful markings under his chin advertise his masculinity to the local lizard ladies… and to rival males too.

Researchers painted a model Water Dragon (actually a plastic iguana with a few glued-on additions) with either brown markings or red markings. (1) The toy was then introduced among resident Water Dragons to record their response to the intruder. When the toy had brown markings, the real Dragons attacked faster and more often.

Those fancy red and yellow stripes attract mates, but also deter rivals.

  1. Baird, TA, TD Baird, and R Shine. 2013. Showing Red: Male Coloration Signals Sam-Sex Rivals in an Australian Water Dragon. Herpetologica 69(4) 436-444

Disruptive Patterns & the Artist-Scientist

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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

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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)

ring_sp_JMLandin_webA 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.