Boback and his team inserted electrodes to monitor electrocardiogram ECG of the heart, blood pressure catheters, and other probes into 24 anesthetised rats before offering them to nine boa constrictors. Seconds after the snakes wrapped their coils tightly around the rats, the scientists watched with amazement as the blood circulation shut down.
With no blood flowing, the brain, liver, and heart were starved of oxygen. The heartbeat became erratic. Had the rats not been anesthetised, they would have quickly lost consciousness. The boas took no longer than eight minutes to kill the rats. Once the snakes feel the heartbeat falter and stop, they relax their muscles and swallow their kill. For the record, the team removed the rats with wires and probes used in the experiment, and fed the snakes with other rats.
Although the scientists studied boa constrictors from Belize, Boback thinks Old World pythons likely kill their prey in a similar manner. This quickly immobilises prey before they can hurt the snakes. Not all constrictors are mammoth snakes. They come in different sizes and eat different kinds of prey. Would they all kill their prey by stopping blood flow like the giant snakes? Baby sand boas no longer than 15 cm. As adults, they often go for birds that forage in the leaf litter, like babblers.
Would lizards and birds be as susceptible to circulatory failure? There is a lot more testing that needs to be done to determine answers to all these questions. To appreciate what constriction means to snakes, one would have to look at their ancestors.
So when an animal gets asphyxiated, that doesn't interfere with the heart, which continues to pump. Because of that, animals continue to benefit from what little oxygen is stored in the blood, at least for a short while.
So all things considered, circulatory arrest is much deadlier. Researchers used boa constrictors and rats to find out how these snakes kill their prey. First, they inserted a number of electronic sensors inside anesthetized rats, to see what happens when a boa starts to squeeze.
Vascular catheters measured the blood pressure inside the circulatory system, while electrodes measured the electrical activity of the animal's heart.
The snake itself was also equipped with a device that can detect the pressure that the snake is generating around the rat. Eventually the snake would strike, and the experiment began. The rats were unconscious throughout. The researchers found that when boa constrictors kill a rat, they squeeze hard enough to interfere with the animal's blood pressure, blood gases, blood ion balance, and heart function.
The study provides a "more detailed explanation than ever before of how constriction subdues even large and strong prey so quickly and effectively," Moon says.
That said, Boback and his team only looked at how boa constrictors kill rats that are about 25 percent of their size, so there's still a possibility that this result is only relevant for mammals, or mammals of a certain size. That's why Boback plans to repeat the study with lizards or frogs. What would happen if you constricted the lizard? These animals don't use oxygen in the same way that mammals do, so it's possible that they don't die in quite the same way when they're squeezed.
The approach helps snakes avoid severe harm from the rat's teeth and claws. Inducing circulatory arrest in prey probably serves two purposes, Moon says. Because circulatory arrest seems faster than suffocation alone, killing a rat by cutting off its circulation might help the snake avoid severe harm from the rat's teeth and claws. In addition, knocking an animal out quickly likely reduces the amount of time and energy that a snake has to spend hunting and eating a single meal.
Boa constrictors were long thought to kill their prey by suffocation, slowly squeezing the life out one ragged breath at a time. But a new study reveals that these big, non-venomous serpents, found in tropical Central and South America, subdue their quarry with a much quicker method: Cutting off their blood supply. When a boa tightens its body around its prey, it throws off the finely tuned plumbing of the victim's circulatory system. Arterial pressures plummet, venous pressures soar, and blood vessels begin to close.
Read how snakes know when to stop squeezing their prey. Most animals can actually survive a relatively long time without breathing: Think about drowning people who are later resuscitated, he says. But the same isn't true for a body without a heartbeat. If executed perfectly, the powerful squeeze causes the animal to pass out within a matter of seconds. Death follows soon after. To better understand the snakes' constriction mechanism, Boback and his colleagues at Dickinson anesthetized lab rats and then rigged the animals with various instruments.
Vascular catheters measured blood pressure, for instance, while electrodes secured within the rats' chest cavities provided information about the heart's electrical activity. Then they fed the outfitted rats to captive boa constrictors and measured what happened to the lab rats. Surprisingly, the pressures at which the snakes cinched against the rats weren't all that remarkable. But then again, they don't need to be. But even this light pressure, when applied to a rat's torso, makes its system goes haywire, the team discovered.
Once blood flow ceases, organs with high metabolic rates—such as the brain, the liver, and the heart itself—begin to shut down. Doctors call this ischemia. The team theorizes that killing by circulatory arrest has given all constricting snakes—which includes pythons and anacondas —an evolutionary advantage.
The quicker the snakes can disable their prey, the lower the chance the predator will get hurt in the process. Think about other animals living alongside boa constrictors in tropical rain forests , says Rosolie: They have teeth, hooves, and claws capable of kicking and ripping.
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