PHOTOPERIODISM
Many plants and animals not only engage in a cycle of daily activities (opening of flowers, waking, feeding, etc.) but also in seasonal activities.
It is not surprising then that both plants and animals mainly depend on photoperiod to prepare for changes in seasonal activities.
And what better way to measure the relative length of day and night than by enlisting the machinery by which circadian rhythms are entrained?
One promising model for photoperiodic responses in plants depends on circadian rhythms. Link to a discussion.
As for animals, recent work with Drosophila suggests that this animal uses two circadian clocks to monitor the changing length of day and night.
In these experiments, Drosophila is using the two clocks to adapt daily — not seasonal — cycles of activity to the changing seasons. But this machinery for measuring photoperiod could enable them to prepare for seasonal changes in activity, e.g., to stop forming eggs at the end of the summer. (However, other studies examining such seasonal changes in Drosophila find that the photoperiodic response is independent of circadian responses. So we must await more experiments to resolve the question.)
- In plants, such things as
- production of flowers;
- making buds dormant in preparation for winter.
- In animals, such things as
- preparing to migrate;
- entering and leaving hibernation.
It is not surprising then that both plants and animals mainly depend on photoperiod to prepare for changes in seasonal activities.
And what better way to measure the relative length of day and night than by enlisting the machinery by which circadian rhythms are entrained?
One promising model for photoperiodic responses in plants depends on circadian rhythms. Link to a discussion.
As for animals, recent work with Drosophila suggests that this animal uses two circadian clocks to monitor the changing length of day and night.
- an "evening" clock that takes over in the long days of summer.
- a "morning" clock that is inhibited by light but takes over when the nights are getting longer;
In these experiments, Drosophila is using the two clocks to adapt daily — not seasonal — cycles of activity to the changing seasons. But this machinery for measuring photoperiod could enable them to prepare for seasonal changes in activity, e.g., to stop forming eggs at the end of the summer. (However, other studies examining such seasonal changes in Drosophila find that the photoperiodic response is independent of circadian responses. So we must await more experiments to resolve the question.)
