Pythons as Model Organisms

As part of the inaugural “Herpetology Blog Carnival” the following post fits within the theme of “Snake Ecosystem Services”.  I have included the links to all of the other blogs on this topic at the end.

benchfly.com

benchfly.com

Having spent many dark hours of my Ph.D. working on a model organism, the nematode worm Caenorhabditis elegans, I have thought long and hard about the limitation of the few organisms biologists tend to work on. The fruit fly (Drosophila), yeast, the African clawed frog (Xenopus), zebrafish (Danio), my beloved worm and of course the mouse receive an inordinate amount of attention from scientists. As a result of focusing in extreme detail on these few species, biologists have been able to advance what we know about a huge number of biological phenomena which are common to most, if not all animals. Yet, despite the strengths of this approach, these model systems have their limitations, and an almost infinite number of interesting biological questions exist that simply can’t be addressed by focusing on these five or six species alone.  Some biologists secretly fear that their model is becoming exhausted—that they will soon be scraping a fruit fly-shaped barrel to come up with interesting data. A new era may now be emerging, where scientists develop novel model organisms in which their chosen biological question can be addressed more directly, and with a high level of resolution thanks to new advances in technology.

Burmese python after eating a deer in the Everglades. Photo Credit: National Geographic

Burmese python after eating a deer in the Everglades. Photo Credit: National Geographic

All this brings me to the Burmese python (Python molurus). The idea to develop a giant snake as a model system was put forth in the late 1990s by the wordy polymath Jared Diamond, and physiologist, Stephen M. Secor.  They were looking for an appropriate organism to study digestive physiology and had done some research with Eric Stein on the sidewinder rattlesnake (Crotalus cerastes). In the past, metabolism and digestive processes were mostly studied in mice, and to a lesser extent in humans. Unfortunately, mice and people are difficult study systems, because both species frequently eat small meals. The sidewinder rattlesnake offered a unique situation of exaggerated digestive processes as the meal size was extremely large, and feeding happened infrequently. Yet, there are some issues with using sidewinders: they’re highly venomous and have to be obtained from the wild. As a result, Secor suggested the Burmese python as a solution. While Burmese pythons may obtain a length over 7 meters and masses just over 100 kg, younger animals may be kept in a lab setting quite easily. They are easy to obtain commercially, are non-venomous and docile. More importantly, they still exhibit the same exaggerated digestive physiology of sidewinders.

Physiologically, these ambush-hunters give a clearer picture of what goes on within the body during cycles of large meal feeding and fasting. A Burmese python can ingest a meal 1.5 times its own body weight. In general, after a meal the gastrointestinal and metabolic rates are greatly upregulated. In addition, cardiac function increases to compensate for the other physiological feats. Because of this additional strain on the heart, this organ can increase in mass by up to 40%. Consequently, the Burmese python has also emerged as a model in which to study cardiac hypertrophy. More recently, Leslie Leinwand and Cecilia Riquelme from CU-Boulder found that although circulating fatty acids and triglycerides increased more than 50-fold after a meal, this actually failed to cause fat deposition on the heart. This means that the right combination of fatty acids may result in beneficial heart growth. Currently, these researchers are working to understand the molecular underpinnings of this phenomenon.

Most recently, the Consortium of Snake Genomics has set out to sequence and annotate the genome of the Burmese python, and is making the transcriptome available for the scientific community at large. This is an important step as it allows this model organism to grow in popularity as genomic resources become readily available. Evidence of this phenomenon is demonstrated by a recent PNAS paper, examining genomic adaptations associated with both metabolism and organ size.

The Burmese Python provides a great example of biologists going outside the comfort zone of model organisms, to use the best animal to answer their research question. It’s also proof that even snakes can be beneficial to understanding human physiology.

Castoe, T.A., Jason de Koning, A.P., et al., 2013. The Burmese python genome reveals the molecular basis for extreme adaptation in snakes. PNAS (early edition http://www.pnas.org/content/early/2013/11/27/1314475110.abstract)

Riquelme, CA, Magida, JA, Harrison, BC, Wall, CE, Marr, TG, Secor, SM, and Leinwand, LA (2011). Fatty acids identified in the Burmese python promote beneficial cardiac growth. Science, 334(6055):528-31.

Secor, S.M. and J. Diamond. 1998. A vertebrate model of extreme physiological regulation. Nature 395:659-662.

Secor, S.M., E.D. Stein, and J. Diamond. 1994. Rapid up-regulation of snake intestine in response to feeding: a new model of intestinal adaptation. Am. J. Physiol. 266:695-705.

Please check out all of the other fantastic stories from the other Herpetology Blog Carnival Members below:

***Snakes and the Ecology of Fear by Bree Putman (Strike, Rattle, & Roll, @breeput) http://strikerattleroll.blogspot.com/2013/12/snakes-and-ecology-of-fear.html

 ***Ecology of Snake Sheds http://snakesarelong.blogspot.com/2013/12/blog-carnival-ecology-of-snake-sheds.html by Andrew Durso (Life is Short but Snakes are Long, @am_durso)

***Good Neighbors Make a Greater Impact http://blog.socialsnakes.org/good-neighbors-greater-impact/by Melissa Amarello (Social Snakes, @SocialSnakes)

***Mark Scherz (The Travelling Taxonomist – @MarkScherz & markscherz.tumblr.com) http://markscherz.tumblr.com/post/69515046243/madagascarsnakeecology

***When the Frogs Go, the Snakes Follow http://australianmuseum.net.au/blogpost/Science/When-the-Frogs-Go by Jodi Rowley (Australian Museum blogs, @jodirowley)

***Kingsnakes Keep Copperheads in Check: http://www.livingalongsidewildlife.com/2013/12/kingsnakes-keep-copperheads-in-check.html by David Steen (www.LivingAlongsideWildlife.com; @Alongsidewild)

***Converting Converting Ophidiophobes to Ophidiophiles, One Kid at a Time http://snakeymama.blogspot.com/2013/12/converting-ophidiophobes-to.html by Emily Taylor (http://snakeymama.blogspot.com/; @snakeymama)

***The Brown Tree Snake of Guam http://snakebytes.tumblr.com/post/69514987068/the-brown-tree-snake-of-guam By Brian Barczyk ( @SnakeBytesTV)

13 Responses to Pythons as Model Organisms

  1. I am glad that snake got that deer and not you. Dang.

  2. Exciting to see all the new biology we can do using snakes as models, particularly given the new genome sequences for python and cobra: http://t.co/QL3hnmzejV

  3. Pingback: Good neighbors make a greater impact | SocialSnakesBlog

  4. Very cool! My former labmate was trying to push children’s pythons as a model organism for physiology. Slightly easier to house than burms.

  5. Fascinating article Heidi, good stuff. Why do you think people are going for burmese pythons over, for example, ball pythons, which are even more readily available, and reach a more manageable size?

    • I have no idea why anyone would want a snake that reached this size. I think they are better looking than ball pythons, but honestly anything that big just isn’t the right pet for the vast majority of people.

    • Great article, very interesting ! I also however agree with Mark, Ball pythons would probably be a much better choice with a better temperament, size and ready availability of captive bred specimens should make them an ideal choice to study.

  6. Great post! I agree that snakes are the ‘new’ model organisms. I also highlight this in my post for the blog carnival.

  7. Mark I think the reason for using burms might have been that they were easy to get and easy to feed… balls can be picky eaters so obviously not so good for digestive physiology studies. They do show the same response- we have used them in class labs. Also remember the snakes are being sacrificed at the ends of the studies to obtain tissue samples, so no need to worry about what happens when they get big.

  8. Wonderful perspective. Although snakes are intrinsically amazing and valuable animals, it’s fascinating that they also have very real and tangible direct benefits to humans.

  9. This is a great summary of how snakes may be used as model organisms in physiology and I want to point out that the case has also been made that snakes can be used as model organisms for ecological studies. Clearly, we should all be studying snakes!

    Shine, Richard, and Xavier Bonnet. “Snakes: a new ‘model organism’in ecological research?.” Trends in Ecology & Evolution 15.6 (2000): 221-222.

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