How To Get A Snake To Stop Constricting

How do boa constrictors know when to stop constricting? Image courtesy of Flickr user wwarby

Ed. note: We welcome back invitee blogger Greg Laden for a two-calendar week blogging bout on Surprising Scientific discipline.

This is a story of snakes, islands and students. Permit'south starting time with the snakes.

Amidst the many different kinds of snakes are the constrictors: boas and pythons. They are shut relatives that diverged millions of years ago. Pythons are constitute in the Former World (Africa and Asia) as well every bit Australia. Boas (family Boidae) are found in the New Globe (North, Central and Southward America including some Caribbean islands). All of them kill their prey by wrapping around it and squeezing it to expiry.

Amidst the boas at that place is an island-dwelling course in Belize that is the subject of interest to conservationists, ecologists and, lately, behavioral biologists. This is the miniature boa of Snake Cayes, a group of islands off the declension of southern Belize. When I say "miniature" I mean that they range in length from xxx cm to about 2 meters (one to 6 feet). This is small compared to the mainland boas of the same species, which can reach 4 meters (13 anxiety) in length.

Information technology is common for animal populations that live on islands to showroom differences in size from those on the mainland. Medium and larger mammals like deer tend to be smaller on islands, small mammals similar rodents tend to exist larger. Something like this may happen with snakes as well.

Allison Hall (left) says "It's a normal thing to exist a picayune afraid of snakes, but you really become into the project and come up to love the animals." Amanda Hayes is on the right. Image provided past Dickinson News and Events

Scott Boback is an expert on these animals, and from the fourth dimension he was a graduate pupil at Auburn University, he's been trying to respond the question "how and why are these snakes pocket-size?"

The almost likely explanations for size differences would seem to exist either diet or other features of the environs, or genetics. Peradventure there is a limited food supply on the islands, and then snakes abound slowly, and thus there are few or no large ones. It would take them so long reach a big size that somewhere forth the line they would have met their demise. Alternatively, it could be that snakes that grow slowly or nigh stop growing as they approach a certain size survive longer or reproduce more effectively (probably owing to food supply being limited). If and so, the genes involved in growth would be shaped by natural selection and over time the island snakes would be small-scale because they are genetically unlike. You can hands imagine how the two processes would work together, maybe with environmental effects working initially simply genetic changes accruing over time.

Boback did somewhen come to a conclusion about the small size of the island boas. He recently told me, "nosotros determined that there is some genetic component to dwarfism on islands. However, nosotros believe that it is actually a combination of genetic and environmental effects that ultimately determine island boa size. That is, growth rates are different between island and mainland boas and this appears to be determined partly by genetics." (See below for the reference to his paper on this research.)

More recently, Boback and his students at Dickinson College accept been addressing a different question about boas: How do they know when to stop squeezing their prey? This is an interesting question because, as you might imagine, contracting the majority of muscles in one'southward body for an extended menstruum of time is energetically costly, but letting go of prey before it is fully expressionless may cause the loss of a meal. As an informal experiment, I asked five different people this question over the past two days, after reading of Boback's research, and everyone gave approximately the aforementioned reply: The snakes allow go when the prey is dead and stops struggling.

Well, information technology turns out that we practice science to prove ourselves incorrect, because that is not the answer. Suspecting a particular mechanism, Boback his students, who maintain a colony of these boas in their lab at Dickinson, devised a vivid experiment. They took a number of dead rats that would normally be fed to the snakes, and installed robotic "hearts" in them. When the snakes constricted the rats, the hearts were allowed to beat for a while, then they were turned off. Soon later on, the snakes loosened their grip, then let go.

It turns out that boas have the ability to observe a heartbeat in the prey, and they use this information to determine how much pressure level to apply. Snakes that had never killed or eaten live prey acted the same equally snakes with experience with live casualty, suggesting that this behavior is innate and not learned.

"Many of the states recollect of snakes as audacious killers, incapable of the complex functions we typically reserve for higher vertebrates," says Boback. "We institute otherwise and suggest that this remarkable sensitivity was a key advocacy that forged the success of the entire serpent group."

One of the bully things about this project is that it involved the efforts of undergraduate researchers. The undergraduates not only participated in the research, but they helped produce the peer reviewed newspaper and are listed as authors. Katelyn McCann, who was a student on this project and now works as a clinical-inquiry coordinator at Children'southward Infirmary in Boston, notes, "I got to experience the true collaborative nature of enquiry as well as the hours of independent work that go into the final product. Now, working in research I feel like I truly understand the scientific method and what goes into any study." Boback adds, "student-kinesthesia research at Dickinson is an opportunity for students to experience science in action. It is the most primal level of learning in science as the educatee actively participates in the process of discovery."

Source:
Boback, S., Hall, A., McCann, K., Hayes, A., Forrester, J., & Zwemer, C. (2012). Snake modulates constriction in response to prey'south heartbeat Biological science Messages DOI: 10.1098/rsbl.2011.1105

Boback, S. M. and D. M. Carpenter. 2007. Trunk size and caput shape in island boas (Boa constrictor) in Belize: Ecology versus genetic contributions. Pages 102-116 in R. W. Henderson and R. Powell, editors. Biological science of the boas, pythons, and related taxa. Hawkeye Mountain Publishing, Eagle Mount, UT.

Boosted information for this story came from Dr. Scott Boback, and a press release from Dickinson College.