Minnesota DNR News-

It’s Officially Spring!

Get excited! Snow piles are melting, temperatures are rising, and day length is increasing! Now that spring is just around the corner, it’s time to break free from our seasonally dormant lifestyle and embrace the pending vernal changes.

Speaking of dormancy, did you know that wildlife species practice multiple types? For example, there’s hibernation, brumation, diapause, quiescence, torpor, and aestivation! Many of these terms get used loosely and synonymously, but each has a specific meaning and describes a specific type of dormancy.

Hibernation is specific to endotherms, like mammals, and is characterized by inactivity, lowered body temperature, and reduced breathing, heart, and metabolic rates. Hibernation was traditionally defined relative to body temperature reduction; however, the term has been redefined and is now based on seasonal metabolic depression concurrent with food scarcity and cold temperatures.

Brumation is similar to hibernation but is specific to ectotherms, like reptiles, and involves different metabolic processes. For example, reptiles accumulate high levels of glycogen in their tissues and blood, allowing them to tolerate lower oxygen levels than hibernating mammals. And unlike true hibernators, brumators will periodically “awake” and drink water to avoid dehydration.

Diapause is a period of developmental arrest initiated in response to a stimulus (e.g., reduced day length) prior to predictable, seasonally recurring environmental conditions (e.g. low winter temperatures). Diapause facilitates survival, synchronizes life history traits with seasonal cycles, and cannot be interrupted until the physiological process has ended. Diapause is typically associated with insects and other arthropods, as well as the embryos of certain fishes.

Comparatively, torpor and quiescence are immediate and relatively short-term responses to unpredictable environmental conditions (e.g., food scarcity). These physiological processes are not seasonally dependent and may last for one day to multiple weeks. Generally, torpor is applied to birds and mammals, whereas quiescence is applied to insects.

Like hibernation and brumation, aestivation is characterized by inactivity and reduced metabolic rates; however, this physiological process is a response to arid conditions and high, rather than low, temperatures. Typically, aestivating species burrow in the soil to avoid heat damage and desiccation; however, some species have evolved clever supporting mechanisms. For example, lesser sirens, which occupy portions of the Mississippi River Valley and the Atlantic and Gulf Coast Plains, survive week- to year-long droughts by retreating deep into crayfish burrows and secreting mucus that hardens into a cocoon and prevents dehydration.

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