Rigor Vitae: Life Unyielding

Tuesday, June 27, 2006

COLOR CHANGE IN KALIMANTAN

Today the WWF announced the discovery of a rare case of a color-changing snake. The reptile is a Kapuas Mud Snake (Enydris gyii), a species described last December, that is known only from the Kapuas drainage system in the Indonesian province of Kalimantan Barat, in Southwestern Borneo. According to the story, Mark Auliya said, “I put the reddish-brown snake in a dark bucket...When I retrieved it a few minutes later, it was almost entirely white.” The article does not mention it, but this quote was not taken fresh from the field, but from an account of a 1996 event in Auliya's Ph.D. dissertation. Dr. Auliya was one of three herpetologists who described E. gyii last winter, based on two specimens he collected from fishermen on tributaries of the Kapuas in '96. The species was named for the late Burmese herpetologist Ko Ko Gyi, whose revision of Enhydris' subfamily, Homolopsinae, is generally accepted today.

The genus Enhydris comprises 23 species, distributed widely throughout Southeast Asia, from Pakistan to New Guinea and Queensland. They belong to the family of typical snakes, Colubridae, and are highly aquatic, often frequenting rice paddies and other standing and sluggish waters, where they feed on fish and aquatic invertebrates which they immobilize with a mild venom that is not particularly dangerous to humans. Their fangs are opisthoglyphic, meaning the venom flows down an open groove in the tooth, and located near the rear of the mouth.

Physiological color change is well known in tetrapods. It is widespread among amphibians, and common in lizards. Strangely, it is very rare among snakes, and the case of E. gyii sounds especially unusual, although three species of dwarf boa (Tropidophis spp.), A Pacific island boa (Candoia carinata), the Round Island Boa (Casarea dussumiereli) and Western Rattlesnake (Crotalus viridis) have all been shown to exhibit this ability to some degree. It is curious that snakes are generally color-fast, and the evolution of physiological color change is sure to be a future post topic. What is equally interesting to me is that the WWF is putting out this press release for a story that is interesting, but obviously not news. This trend reminds me of a visit I paid to the Aquarium in Seaside, Oregon, some 20 years ago. One of the tanks housed a group of nondescript brown cod. In order to jazz up the exhibit, they illuminated it with green lights in the back, and blue ones up front. The sign explained that the fish had the uncanny ability to change their eye color from green to blue at will, and, sure enough, as they swam from the front of the tank to the back, the color of their eyeshine shifted. The end result was to make the fish seem more mundane than they really were—as if the management felt they had to apologize for them. The biology of Borneo is plenty fascinating and plenty imperiled. That fact can be communicated easily enough without resorting to hyperbole.
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Photograph of Enhydris gyii taken by Mark Auliya

4 Comments:

Blogger Sivasothi said...

You can download the paper.

2:55 AM  
Blogger cpbvk said...

Thanks for the link, Sivasothi. It leads to a page from the site of the wonderful Raffles' Museum in Singapore. A link from that page will give you a pdf of the original species description by Murphy, Voris and Auliya.

2:59 PM  
Blogger monado said...

I noticed that the article was old news. Perhaps a "dog days of summer" tactic in the news room, as though nothing is happening in the world of science?

I was puzzled why the article didn't address the nature of the colour change. The article called it a "chameleon snake," implying that it might change to match its background. But it was placed in a dark bucket and turned white. That sounds more like a fear reaction—pale with fear— with the possible effect of playing dead. Thoughts, anyone?

7:30 AM  
Blogger cpbvk said...

It's very common for reptiles and amphibians to turn lighter at night, especially in nocturnal species like geckos, dwarf boas and frogs, but chameleons do this too. I think the benefit has more to do with thermoregulation than with camouflage. It is surprising to me that an aquatic snake would exhibit such strong color change. I don't know anything about day/night color change in fish, and it would be interesting to look into how they might compare with the snake.

9:45 AM  

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