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Clocks in Living Things: Daily & Seasonal Rhythms

Explore the intricate world of circadian and circannual clocks in living organisms, controlling daily and seasonal timing through genetic pathways. Discover how these internal rhythms regulate behaviors, gene expression, and vital survival strategies such as reproduction, hibernation, and migration. Gain insights into the impact of light on melatonin release and its effects on sleep patterns. Delve into the fascinating mechanisms at play in plants and animals that are finely tuned to respond to environmental cues and genetic adaptations.

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Clocks in Living Things: Daily & Seasonal Rhythms

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  1. Circadian and Circannual Clocks in Living Things Daily and Seasonal Timing

  2. Many Living Things Have a Internal Clocks DAILY SEASONAL Regulates seasonal changes in gene expression and behavior • Regulates daily cycle of activities

  3. Circadian Rhythm are Endogenous • Occur internally- do not require environmental cues • BUT can be altered by environmental cues

  4. Under Genetic Control • We have genes that control these rhythms • But environment can change gene expression

  5. Evolutionary Adaptations • Daily and seasonal changes are genetic characteristics that have evolved because their presence is advantageous • Natural selection has favored these traits

  6. Circadian Rhythms in Plants • Change in leaf orientation • Opening of stomata – pores in the leaf • Opening of flowers and release of fragrance

  7. Observations of Plants • Leaves happened at nearly same time every day, even on cloudy days • BUT artificial light at different times confuses the plant’s internal clock

  8. Circadian Rhythm in Animals • Closely tied to sleep-wake cycle

  9. Why You’re Stressed in the Morning

  10. Light Might Inhibit Melatonin Release • Melatonin thought to control sleep urges • Concerns artificial lights prevent melatonin release and keep people awake

  11. Seasonal Clocks • Affect gene expression • Control things like: • Shedding of coats • Reproduction • Hibernation • Migration

  12. Photoperiodism in Plants • Plants measure length of night • Certain night length triggers flowering

  13. How? • Light changes structure of phytochrome protein • Longer the darkness, the more Pr there is

  14. Short Day vs. Long Day Plants Flower in spring/summer

  15. In Animals • Light absorption by the eye triggers change in gene expression • Thought to be mediated by melatonin

  16. Shedding of Coats or Changing of Color • Arctic Wolf in Summer • Arctic Wolf in Winter

  17. Seasonal Reproduction • Many species only reproduce in spring or summer • When more food (energy) is abundant

  18. Ex. How Seasons Affect Reproduction in Animals

  19. Hibernation • Helps conserve energy when little food available

  20. Migration • Changes in light trigger hormone changes • As there’s less light birds build up fat for journey • BUT also occurs in birds in captivity with consistent light sources • BUT reducing light brings about changes in behavior

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