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

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

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