Home & Garden Columns
Although you wouldn’t expect a book about metabolic ecology to be a page-turner, I found John Whitfield’s recent In the Beat of a Heart: Life, Energy, and the Unity of Nature engrossing. Whitfield, a British science journalist, explains how metabolism relates to size, volume, and surface area. Along the way, he looks at why bats outlive mice, whether humans are allotted a fixed number of heartbeats in their lifetime (astronaut Neil Armstrong said that if that was true, he was damned if he was going to waste any of his jogging), and the tragic fate of Tusko the elephant.
Tusko, a bull Asian elephant at the Oklahoma City zoo, was the recipient of the largest hit of LSD ever administered to a living organism—297 milligrams, right in the rump, back in 1962. Psychiatrist L. Jolyon West was trying to induce musth, a state of apparent derangement to which male elephants are prone during the breeding season. West and his associates calculated the dose by extrapolating in linear fashion from the amount required to make a cat hallucinate.
It was too much, of course. Tusko staggered despite his mate Judy’s attempts to support him, trumpeted, collapsed on his side, and began having seizures. He was pronounced dead an hour and 40 minutes later. Scale matters. The results were published in the prestigious journal Science, with the following summation: “It appears that the elephant is highly sensitive to the effects of LSD—a finding which may prove to be valuable in elephant-control work in Africa.”
Size isn’t the only variable affecting metabolism. Some creatures are able to bank their internal fires during periods of extreme cold or heat and scarce resources, living on stored body fat: aestivating ground squirrels, hibernating bears, those male emperor penguins guarding their eggs through the Antarctic winter. It’s a risky strategy. Once fat levels fall below 10 percent of body mass, the animal has to burn its own protein—effectively digesting itself.
Snakes, like other living reptiles, were known to keep their thermostats set lower than mammals or birds (the dinosaurs may have been different). But it was unclear until recently how they endured periods of food deprivation. As you will have noticed if you’ve ever handled a snake—something I would recommend, although not necessarily in a spiritual context—snakes don’t have much fat on them.
To explore that question, Marshall McCue, a graduate student at the University of Arkansas, worked with captive ball pythons, rat snakes, and western diamondback rattlesnakes. The reptiles, in cages that constrained their activity, were kept at a constant 80.6 degrees F, limiting their body temperatures. They were deprived of food for up to 168 days while McCue recorded their oxygen consumption. Snakes were sacrificed at various set points during the experiment and their fat and protein levels measured; McCue went through a lot of snakes during this project.
The snakes were able to lower their resting metabolic demands by up to 72 percent. “It would seem that their pilot light, which we already thought to be as low as possible, can actually go much lower,” McCue told a reporter for Nature. Their fat levels fell to 5 percent, which would have doomed most other vertebrates.
And they accomplished this without going dormant. They stayed alert enough to attempt to bite their handlers; if a tasty rat had been offered, they would have been right on it. Some even managed to grow while starving.
The rat snakes began to break down protein sooner than the rattlers or pythons, which makes ecological sense. Rat snakes are active pursuit predators; the others are ambush predators, more likely to experience significant lag time between meals. But the fact that snakes from three diverse lineages, including the relatively underived (it’s bad form to say “primitive”) pythons, share the ability suggests it’s an ancient trait in this group of reptiles.
McCue uses an economic metaphor: the snakes reduce energy demand by lowering their metabolic rate and cope with the supply side by frugal use of their fat reserves. Just how they do this remains uncertain: maybe by reducing the density of mitochondria—the energy-generating powerhouses of the cells—in liver, heart, and other highly active tissues.
All this may explain how snakes lucked out at the end of the Cretaceous, when some combination of extraterrestrial impact and volcanism killed off the dominant reptile groups—the dinosaurs, the pterosaurs, the great sea dragons. With whole ecosystems trashed and food webs disrupted, being able to just shut down for a few months would have had enormous survival value.
According to McCue, the snake study may have practical spinoffs in monitoring nutritional success—more than can be said for the experiment that left the unfortunate Tusko a martyr to science.
Photograh by Ron Sullivan. A gopher snake relaxing between meals near the Richmond shoreline.
Joe Eaton’s “Wild Neighbors” column appears every other Tuesday in the Berkeley Daily Planet, alternating with Ron Sullivan’s “Green Neighbors” column on East Bay trees.
Department of Corrections: the photograph of the California clapper rail accompanying my Arrowhead Marsh article was taken by Ron Sullivan.