Cold, hard winter

Mammals are known as endotherms — warm-blooded — while reptiles and amphibians are known as ectotherms — cold-blooded. Many endotherms and most ectotherms in northern latitudes survive winter by hibernating. Mammalian hibernation has received more notoriety because of the dramatic drop in metabolism needed to reach a torporus — low metabolic — state.

Hibernating ectotherms begin with a metabolic rate often 10 times lower than mammals and that rate normally drops by another 10 to 20 percent during hibernation. However, when one stops and looks at ectotherm hibernation one finds many interesting and some downright amazing stories.

Ectotherms appear to sense the same environmental clues like the change in day length, as migrating and/or hibernating birds and animals. Many will enter a dormant state at the same time each year even if local conditions don’t necessarily call for it.

The most important thing for ectotherms is the avoidance of freezing. The damage suffered by ectotherms from freezing is internal, not external. Ice crystal form in the animal’s intercellular water. These jagged crystals can destroy cells and tissue resulting in death.

Hellbenders and other aquatic salamanders often remain somewhat active year-round. Even some terrestrial salamanders like the redback may be found out and about on warm winter days.

Survival for most ectotherms means finding a hibernaculum below the frost line. Terrestrial ectotherms may dig or burrow or usurp burrows or find crevices in rocks or tunnel under large logs to get below the frost line.

Aquatic ectotherms find deep pools, below the frost line. Most aquatic frogs are content to simply lie on the bottom in the mud. Turtles prefer to bury themselves in the mud. While these turtles and frogs are highly adapted to an aquatic life they still must have oxygen to survive. Turtles have special tissues with minute blood vessels in their throat cavities and near their anus that allow them to extract oxygen from the water. Amphibians like frogs can actually absorb oxygen through their skin.

Some terrestrial frogs that aren’t good diggers have developed a rather miraculous method of surviving the rigors, or rigormortis, of winter. These frogs may crawl beneath the leaf litter or sink in the snow at the Arctic Circle, but that’s about as deep as it gets. When that litter or snow freezes, so do the frogs, adding a bit of a twist to the idiom “long hard winter.”

Four species of frogs that may spend part of their winter as frogcicles can be found in Western North Carolina. They include wood frog, spring peeper gray tree frog and upland chorus frog.

Cryogenics is crying out for these “lower” animals’ secret. As mentioned earlier, the damage done when amphibians freeze is internal. These frogs that survive freezing fend off internal freezing by releasing glucose into their cells. The glucose acts like natural antifreeze, preventing the delicate cell tissue from freezing.

For all practical purposes, these frogs are frozen to death. Their heart stops beating, they stop breathing and all brain activity ceases. However, the glucose antifreeze prevents the cells from freezing and when the temperature once again rises above freezing the frogs are as hoppy as ever.

(Don Hendershot can be reached at ddihen@juno.com.)