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Hibernating turtles don’t slip into a coma

Winterized red-eared sliders shut down their lungs but still respond to light

SURVIVING SHUTDOWN  Freshwater turtles like this red-eared slider hibernate in oxygen-poor waters in winter. Researchers thought they were in a nonresponsive coma, but they can still detect light, a study finds. 

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A chilled, hibernating turtle that hasn’t taken a breath for two weeks still notices light, a new lab study shows.

That response contradicts a widespread notion that freshwater turtles overwintering under ice go into nonresponsive comas, says animal physiologist Jesper G. Madsen of Aarhus University in Denmark.

Many freshwater turtles avoid freezing during winter by retreating to the depths of lakes. When ice smothers the water, the air-breathing turtles can find themselves nearly starved for oxygen. These turtles can do remarkable wintertime shutdowns: metabolism slows and inhibiting compounds essentially self-anesthetize much of the animals’ nervous systems. Madsen wondered, however, if the animals retained some ability to detect early-season environmental cues rather than just waiting to warm up again in spring.

In lab tests, vibrations didn’t elicit much response from red-eared sliders (Trachemys scripta) that had been on winter shutdown for 14 days. Yet turning on lights set the animals moving more than they had in the dark, the researchers report October 9 in Biology Letters. In the wild, as ice finally cracks, light streaming through could signal to turtles that it’s time to swim up for a breath of air.

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