Thursday, 25 December 2014

Flying Dragons Pretend to Be Leaves to Avoid Predation

Draco cornutus, one of the many flying dragons
Draco cornutus
Credit: Dr. Devi Stuart Fox
A new study by researchers at the University of Melbourne suggests that Draco Cornutus, a species of gliding lizard from Borneo, mimicks  the red and green colors of the falling leaves to avoid falling prey to birds whilst gliding.

According to the study, D. cornutus have evolved extendable gliding membranes, like wings, which closely match the colors of falling leaves to disguise themselves as they glide from tree to tree in the rainforest.

Found throughout South-East Asia, lizards of the Draco genus are the only lizards to feature extendable gliding membranes -called patagia- which enable them to glide between trees in their territories. These lizards are commonly known as flying dragons or flying lizards.

The study appeared yesterday in the international journal Biology Letters and was conducted by PhD student Ms Danielle Klomp, based at both the University of Melbourne and the University of New South Wales with supervisors Dr Terry Ord and Dr Devi Stuart-Fox and collaborator Dr Indraneil Das from the University of Malaysia.

The scientists traveled to Borneo and observed two distinct populations of  D. Cornutus that have different colored gliding membranes and occupy very different habitats.

Draco taeniopterus, another flying lizard
Draco taeniopterus
Credit: Psumuseum
The first population has red gliding membranes, which match the color of the red falling leaves of their coastal mangrove forest habitat. The second has dark brown and green gliding membranes, which match the colors of falling leaves in their lowland rainforest habitat.

They determined how the colors would be perceived by a predatory bird and found that the gliding membrane color would be indistinguishable from a falling leaf in the same forest.

Birds can see ultraviolet light as well as the colors that humans see, so it is important to take into account how closely the colors would actually match to a bird, Ms Klomp said.

"It's a cool finding because these gliding lizards are matching the colours of falling leaves and not the leaves that are still attached to the tree. In the mangrove population the leaves on the trees are bright green, but turn red shortly before falling to the ground, and it is this red colour that the lizards mimic in their gliding membranes. This allows them to mimic a moving part of the environment- falling leaves -- when they are gliding." Ms Klomp said.

Because some animals have developed color not only for camouflage, but also as a form of communication, the scientists also wanted to watch the lizards interact in the wild and determine whether their gliding membranes were used for communication as well as gliding, said Ms Klomp.

The team also filmed hours of flying lizard behavior to observe how often these colors were displayed to other lizards.

"We found that both the red and green/brown gliding membranes seem to have evolved to specifically resemble the falling leaves in each population's particular habitat, and are rarely used for communication. 
 Perhaps these populations may have originally had the same gliding membrane colours but as they have moved into different forest types their colours have adapted to closely resemble the colours of falling leaves in the different forests, known as divergent evolution." Ms Klomp said.
The most popular flying dragon, Draco Volans
Draco Volans

References
- Klomp, D., Stuart-Fox, D., Das, I., & Ord, T. (2014). Marked colour divergence in the gliding membranes of a tropical lizard mirrors population differences in the colour of falling leaves Biology Letters, 10 (12), 20140776-20140776 DOI: 10.1098/rsbl.2014.0776

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