What if an organisms doesn't have a 24 hour day/night cycle?
An article from Project Neuron ex University of Illinois:How do reindeer tell time?
Nearly every organism on the planet has daily rhythms. These rhythms follow external light-dark cues from the sun, but are present also in constant darkness. Many animals, including humans, have internal clocks that are set to approximate 24-hour periods. This article describes research reported in Current Biology, investigating the internal clock of an animal that does not have a 24-hour day-night cycle, the reindeer.
Animals all over the world are confronted by environments that demand specialized behavioral and metabolic responses in order to survive.
Daily rhythms, guided by an internal clock, are considered to be a fundamental feature of all living things. The mammalian circadian clock is located in an area of the brain called the suprachiasmatic nucleus (SCN). Usually this clock is controlled in part by light-dark (day-night) cues. However, even when organisms are in constant dark conditions, they will exhibit near-24 hour rhythms in their activity. Organisms use their clocks to match their behavior to the 24-hour environment, measure the length of day, navigate by the sun, and organize their body functions.
But if the light environment does not change on a 24-hour basis, would a circadian clock be a help, or a hindrance? Animals live in the depths of the ocean, far under the ground, or at the poles—where there is not a 24-hour day-night cycle of light and darkness. Reindeer, living in the Arctic, are being studied to investigate how the internal clock works in an environment where the sun neither rises nor sets.
One study found that reindeer lack the underlying oscillatory machinery necessary for guiding circadian rhythmicity. Reindeer do not have daily rhythms in activity when the sun remains constantly above or below the horizon (peak of summer and winter). Even during times of the year when there are light-dark cycles, reindeer do not have constant activity patterns.
Just as reindeer activity patterns do not have daily cycles; their cells also lack the daily patterns of transcription and translation that are present in the cells of nearly every other animal.
Scientists think that the reindeer’s “silent clock” may be an advantage for surviving in an environment where the day length is always changing.
Text and image adapted from
Paul, M.J., and W. J. Schwartz. (2010). Circadian rhythms: How does a reindeer tell time? Current Biology 20: 280 – 282.
Guided Reading Questions:
Nearly every organism on the planet has daily rhythms. These rhythms follow external light-dark cues from the sun, but are present also in constant darkness. Many animals, including humans, have internal clocks that are set to approximate 24-hour periods. This article describes research reported in Current Biology, investigating the internal clock of an animal that does not have a 24-hour day-night cycle, the reindeer.
Animals all over the world are confronted by environments that demand specialized behavioral and metabolic responses in order to survive.
Daily rhythms, guided by an internal clock, are considered to be a fundamental feature of all living things. The mammalian circadian clock is located in an area of the brain called the suprachiasmatic nucleus (SCN). Usually this clock is controlled in part by light-dark (day-night) cues. However, even when organisms are in constant dark conditions, they will exhibit near-24 hour rhythms in their activity. Organisms use their clocks to match their behavior to the 24-hour environment, measure the length of day, navigate by the sun, and organize their body functions.
But if the light environment does not change on a 24-hour basis, would a circadian clock be a help, or a hindrance? Animals live in the depths of the ocean, far under the ground, or at the poles—where there is not a 24-hour day-night cycle of light and darkness. Reindeer, living in the Arctic, are being studied to investigate how the internal clock works in an environment where the sun neither rises nor sets.
One study found that reindeer lack the underlying oscillatory machinery necessary for guiding circadian rhythmicity. Reindeer do not have daily rhythms in activity when the sun remains constantly above or below the horizon (peak of summer and winter). Even during times of the year when there are light-dark cycles, reindeer do not have constant activity patterns.
Just as reindeer activity patterns do not have daily cycles; their cells also lack the daily patterns of transcription and translation that are present in the cells of nearly every other animal.
Scientists think that the reindeer’s “silent clock” may be an advantage for surviving in an environment where the day length is always changing.
Text and image adapted from
Paul, M.J., and W. J. Schwartz. (2010). Circadian rhythms: How does a reindeer tell time? Current Biology 20: 280 – 282.
Guided Reading Questions:
- What is the function of the mammalian suprachiasmatic nucleus?
- Why do many animals have 24 hour rhythms, even in constant light conditions?
- The extreme North and South are regions without constant light-dark cycles. Where else might there be an inconsistent light-dark cycle, or even no light cycle at all?
- In the regions you describe above, what would you expect to observe in the circadian rhythms of the species who live there?