The big squeeze: scaling of constriction pressure in two of the world's largest snakes, Python reticulatus and P. molurus bivittatus

Abstract

Snakes are important predators that have radiated throughout many ecosystems, and constriction was important in their radiation. Constrictors immobilize and kill prey by using body loops to exert pressure on their prey. Despite its importance, little is known about constriction performance or its full effects on prey. We studied the scaling of constriction performance in two species of giant pythons (Python reticulatus and Python molurus bivittatus) and propose a new mechanism of prey death by constriction. In both species, peak constriction pressure increased significantly with snake diameter. These and other constrictors can exert pressures dramatically higher than their prey's blood pressure, suggesting that constriction can stop circulatory function and perhaps kill prey rapidly by over-pressurizing the brain and disrupting neural function. We propose the latter 'redout effect' as another possible mechanism of prey death from constriction. These effects may be important to recognize and treat properly in rare cases when constrictors injure humans.

The king of snakes: performance and morphology of intraguild predators (Lampropeltis) and their prey (Pantherophis)

“…Although both morphology and physiology are important, behavior can determine the ways in which morphological elements and physiological capacities are used (Hertz et al, 1982). For snakes that use constriction behavior, predation performance can be evaluated by measuring peak constriction pressure (Moon, 2000;Moon and Mehta, 2007;Boback et al, 2015;Penning et al, 2015;Penning and Dartez, 2016). Constriction pressure is a biologically important measure of performance (Moon and Mehta, 2007) because it can determine the time needed to subdue the prey and reduces the chances of prey escaping or causing injury to the snake.…”

“…all the muscles on the concave parts of a constriction coil or on the concave parts of multiple axial bends used in pulling movements). Larger snakes have more muscle CSA (Moon and Mehta, 2007); therefore, changes in body size can be expected to have significant effects on these measures of performance in snakes (Moon and Mehta, 2007;Penning et al, 2015;Penning and Dartez, 2016). Although a priori expectations can be generated regarding the scaling of muscle force (Pennycuick, 1992), constriction pressure is much more variable (Moon and Mehta, 2007;Penning et al, 2015;Penning and Dartez, 2016) and depends on the area of contact and force exertion.…”

“…Larger snakes have more muscle CSA (Moon and Mehta, 2007); therefore, changes in body size can be expected to have significant effects on these measures of performance in snakes (Moon and Mehta, 2007;Penning et al, 2015;Penning and Dartez, 2016). Although a priori expectations can be generated regarding the scaling of muscle force (Pennycuick, 1992), constriction pressure is much more variable (Moon and Mehta, 2007;Penning et al, 2015;Penning and Dartez, 2016) and depends on the area of contact and force exertion. It is not clear a priori how the surface area of contact should change with size during the dynamic interaction between predator and prey (Penning et al, 2015).…”

“…Although a priori expectations can be generated regarding the scaling of muscle force (Pennycuick, 1992), constriction pressure is much more variable (Moon and Mehta, 2007;Penning et al, 2015;Penning and Dartez, 2016) and depends on the area of contact and force exertion. It is not clear a priori how the surface area of contact should change with size during the dynamic interaction between predator and prey (Penning et al, 2015). Given that the relationship between constriction pressure and the surface area of contact has not yet been quantified for snakes of any size, we do not have enough information to generate testable hypotheses about the predicted scaling of constriction pressure with body size.…”

“…Given that the relationship between constriction pressure and the surface area of contact has not yet been quantified for snakes of any size, we do not have enough information to generate testable hypotheses about the predicted scaling of constriction pressure with body size. Although constriction pressure and pulling force are distinct variables that are typically related to different behaviors, they are appropriate indicators of predation and escape performance in snakes (Moon, 2000;Lourdais et al, 2005;Moon and Mehta, 2007;Boback et al, 2015;Penning et al, 2015;Penning and Dartez, 2016). Therefore, they can be compared across species and sizes to understand the factors that affect the outcome of this predator-prey interaction.…”