Chronicle of a chemical war – Liberation
« Opium, come here! » In Montpellier, even dogs have narcotic names. The Pitbull complies and joins its master. I am delighted doubly. Firstthe Molosse without a leash or muzzle moves away from me while I cross the Montmaur wood on this hot spring day. Secundothe dog was heading for a superb Montpellier snake, and fortunately turns around. The green-yellow reptile, which measures much more than a meter long, quietly crosses the path at my feet and disappears in a thicket. The almost meeting between the dog and the snake was mainly dangerous for the latter: the billion domestic canins in the planet, not happy to bite tens of millions of humans each year, also kill hundreds of millions of wild animals.
Opium will not taste the venom of the snake. This chemical bite was, in any case, almost impossible, because the hooks of the beautiful reptile are located on the rear part of the upper maxilla; The snake should have swallowed the dog’s tail, or the owner’s finger. Opium, or his master, would then have felt strong pain, followed by edema and some neurological symptoms without much consequence. For the usual prey of snakes, especially rodents, the venom of snakes is of course fatal, but a recent study indicates the astonishing capacity of small mammals to modulate the toxicity of the venoms of reptiles according to the climate and their diet.
In the southwest of the United States, in the deserts of Mojave and Sonora, the crotals hunt neotomas, rodents of ten centimeters with great mice. The venom of the bell snakes is fatal for neotomas, which nevertheless developed defense mechanisms, in particular by inhibiting the enzymes contained in the venom. But the neotomas face a second threat: they mainly eat creosotiers, these bushes of the deserts that the westerns show us, rolling in a ball in the wind. Creosotiers, to defend themselves from snacks, are extremely toxic. The organization of neotomas must therefore detoxify their food, as well as the venom of the crotals to which they are regularly exposed. To top it all, reptiles and mammals undergo variable temperatures depending on the seasons and daily cycles. These thermal environments have an impact on the movements of prey and their predators, potentially also on the ability of neotomas to inhibit the toxins that attack them.
In order to unravel this strange drug trafficking, Matthew Holding and his colleagues from four American universities have raised neotomas at different temperatures by nourishing some of Creosotier resin, the others with food without toxins. They subsequently measured the resistance of rodent serum to Crotale venom. Their analyzes show that when neotomas are a little cold, at 21 ° C, their capacity for inhibition of venom is only 13 %. On the contrary, when neotomas live at 29 ° C, a temperature that is pleasant to them, their inhibition capacity is 68 %. Nevertheless, the consumption of creosotier reduces the potential for inhibition of venom by 18 %.
For the research team, these results are explained by the fact that the crotals are much more active at 29 ° C than at 21 ° C, and in order to attack the neotomas. In response, neotomas seem to strengthen their anti-venine protections in hot weather. Field observations also show that rodents eat less when temperatures are high, and therefore need to detoxify their food.
As the authors conclude « The balance between the search for food and the risk of predation goes beyond the behavioral choices that dictate exposure to predators, and extends to physiological susceptibility to toxic challenges ».
For Philippe Geniez, specialist in reptiles at the CEFE-CNRS in Montpellier, « The resistance of the neotomas is really astonishing, because the venom of the crotale is considerably more powerful than that of the Montpellier snake, however very effective on the prey it consumes, in particular reptiles, small mammals to the size of a young rabbit, and birds ».
