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Monthly Newsletter Spotlight

Life in the Cold

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Hurricane Ridge in Winter. Photo by National Park Service.

by Cheryl Lowe

Our recent record cold temperatures had me re-reading a favorite book from my time in New England. Life in the Cold: An Introduction to Winter Ecology by Peter J. Marchand, now in its 4^th edition, is still recognized as one of the best introductory primers on winter ecology. My appreciation of nature in winter has been forever enhanced by this book. With the following, I share a bit of what I find particularly fascinating, in hopes you, too, will see winter with fresh eyes.

When the temperatures drop we put on an extra layer of clothes, turn up the heat to keep pipes from freezing, and maybe head out to enjoy snow-dusted trees and trails. For plants, animals and insects, the options for enduring and surviving winter weather are very different.

Hibernation

Hibernating is often the first adaptation that comes to mind. That strategy still requires storing enough energy reserves to rewarm and arouse periodically for a somewhat unknown period of time. I knew that hibernating animals will arouse periodically, but didn’t know why. Arousal (variable, of course, based on the species being discussed) seems to be necessary for certain metabolic functions such as immune response, defecation or even sleep (since sleep is a resting state where unconscious functions continue) even if the hibernating animal is not eating from winter stashes of food.

Snow pack as shelter

The structure and ‘behavior’ of snowpack is a critical component of survival for many species. We know that snow can be a blanket of insulation. Hidden from view, however, is the subnivean zone (https://en.wikipedia.org/wiki/Subnivean_climate). As snow accumulates, the snowflake’s delicate water crystals fuse and merge, melt and metamorphose into denser snow that settles and holds together. When snow cover is at least six inches deep, the soil’s warmth melts the lowest layer of snow and creates a gap between soil and snow that gives mice, voles and other small mammals space to forage for insects and seeds.

Plants in winter

In general, the above-ground parts of plants exposed to freezing temperatures survive by increasing their resistance at the cellular level to the damaging effects of freezing and ice formation. Water migrates out of individual cells through a cell membrane that gradually becomes more permeable as the plant acclimatizes and moves into the spaces between cells where ice crystals can form without damaging cell tissue.

Many people assume that winter damage such as crispy, brown leaves they see on their evergreen garden plants is caused by desiccation, but studies have shown that most of the water that these plants need in winter is supplied by internally stored water, not from frozen ground. It seems more likely that the damage is caused when sun-warmed leaves (where water has moved back into cells) experience rapidly dropping temperature at night, freezing the cells and injuring them.

Illustration of life underneath the snow, by Kristin Link.

Fish (of course)

Cold-water fish tend to have thicker bodies and layers of fat for insulation, helping to retain body heat. Fish in colder environments also have slower metabolic rates, allowing them to conserve energy and cope with reduced food availability during colder seasons. They also have the ability to produce antifreeze proteins that lower the freezing point of their body’s fluids. These proteins adhere to ice crystals as they first form, preventing the continued growth of ice crystals that can damage their cells.

Amphibians

Reptiles and amphibians also hibernate (it’s called brumation in cold-blooded animals.) Depending on the species, they may seek shelter underground in rock crevices, decaying logs or even in the burrows of other animals in winter. Toads, frogs and salamanders may also head for the soft mud of pond bottoms, caves or seepage areas that do not freeze.

As temperatures drop, some salamanders and newts are also able to gradually adjust their metabolic rate so they maintain the same metabolic rate in colder temperatures. They do this by changing the types of enzymes used to control their metabolic processes.

Land-hibernating frogs such as the Pacific chorus frog are freeze tolerant. As their bodies freeze, their heart and breathing stops, but they are kept alive by the minimal anaerobic metabolism of their energy stores and the protective action of glucose. These frogs can slip in and out of a frozen state quickly.

Insects

The incredible diversity of the insect world is reflected in the diversity of cold-tolerance strategies they use. One adaptive strategy for insects is supercooling**. This is accomplished by producing compounds such as glycerol, certain blood sugars, or antifreeze proteins that lower the freezing point or supercooling point of their body’s fluids, or by blocking ice formation in the first place, as described in the fish section above. Insects, like plants, can also move excess water out of their cells and into the intercellular spaces, where it is safer for ice crystals to form.

For many of us, winter is a time when plants ‘die back’ or ‘go dormant’ and the world is quiet. But now, when I put on my extra warm layers and venture out, I’m much more aware of what is happening underground, in burrows and under the snow. That cold, snowy trail is now an affirmation of the myriad adaptations that plants and animals are using to survive in winter.

Definitions and Resources

** Supercooling is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. It is achieved in the absence of a seed crystal or nucleus around which a crystal structure can form. Wikipedia

Life in the Cold: An Introduction to Winter Ecology, by Peter J. Marchand. 2014. University Press of New England.

Hibernation:

https://morgridge.org/story/what-we-can-learn-from-hibernation-qa-with-hannah-carey/

https://education.nationalgeographic.org/resource/some-animals-dont-actually-sleep-winter-and-other-surprises-about-hibernation/#

Fish

https://www.quora.com/What-adaptations-do-fish-have-to-survive-in-extremely-cold-or-hot-environments)