Seasonality & Coincidence Flashcards
3 different mechanisms used to determine time of year
Problems?
Direct observation (of sun, leaves, enviro, clothing, weather, etc)
- Mistakes in weather
- Incorrect interpretations
Annual clocks (able to anticipate certain times of year)
- Not a lot of evidence that clock was necessary (bcuz of ability to observe)
Photoperiodic time measurement
4 studies that show rhythms showing annual clock:
Human conception rate
Diurnal squirrel locomotor activity
Marmots from Europe to South America
Kenyan vs European stonechats
1) Rate was in bimodal distribution (April-May + September-October)
- Conception decreased in spring and increased in fall after 1940s bcuz women went into workforce
2) Diurnal squirrels kept in same L/D cycle (no sense of time of year)
- Entrainment occurs but activity still changes depending on season
3) Peak body weight of Marmots change throuughout day
- Shifted 12 hours gradually after moving to South America to match environment
4) Stonechats used to be migratory birds w/ small peak in Nov and big peak in March (Same photoperiod)
- Shows that they’re settable by a photoperiodic Zeitgeber and have memory of length of season
Photoperiodic induction
Ability of an organism to use circadian system and measuring on/off of the light instead of the photoperiod
(Needs a photosensitive part on the organism that expects a period of no light)
Photoperiodic induction of short day (chrysanthemum, blooms in fall) and long day plants (hyoscyamus, blooms in spring)
How many hours of sun for short day and long day plants?
As number of hours of sun increases, chrysanthemum flowering is inhibited and hyoscyamus flowering increases
Short day - 8-10 hours of sun
Long day - 14+ hours of sun
Photoperiodic induction in short day and long day butterflies
- Acronycta rumicis (Long day, 20-35 hrs of light)
- Bombyx mori (Short day, 0-12 hrs of light)
Why is this important?
Acronycta diapause (leaving cocoon) inhibited on short days
Bombyx inhibited on long days
Allows butterflies to become adults of each species at same time of year
Phase angle of entrainment depends on photoperiod (Syrian hamster study)
- Photoperiod is increased each day
At short photoperiod (dark for 24 hrs), activity onset at 12 hours ahead of light or behind dark (phase angle = 12 hrs)
- Pattern continues until half light, half dark day
- When night gets shorter, activity gets delayed bcuz hamster doesn’t want to run in light
Photoperiod determines reproductive state (Syrian hamsters)
- Testes weight
Circadian period determines reproductive state (Syrian hamsters)
- Testes weight depending on circadian period
Testes increase greatly when photoperiod is 12 hrs or longer
- Happens in spring
Hamsters at photoperiod 12 had some large and some small testes
- Cycle length (phase angle of entrainment) of 24 hrs had smallest testes size
- Delayed phase angle causes light at end of night, advanced phase angle causes light at beginning of night
- W/ 24 hr cycle, no light at beginning or end of night
** After 8 weeks in DD, tested will eventually grow
External coincidence
Internal coincidence
When light hits the nocturnal part of a circadian cycle, photoperiodic response is initiated (assumes that it’s spring or summer)
- Ex: Presence of light and subjective night overlap
Light-entrainable oscillator is moved outside of specific range of phase angle w/ a slave oscillation, causing photoperiod response
- Ex: Phase angle of melatonin oscillation is driven to a new phase relationship w/ a melatonin-sensitive oscillator
Resonance experiment w/ flowering (Light pulse experiment)
Plant (both short and long day plants) assumes that it’s a long day when ZT is a multiple of 24 hrs
Night break experiment w/ flowering:
Did short and long day plant flower w/ less light, more light, more light + distributed into night?
Short:
- Short day - Flowering
- Long day - No flowering
- Short day w/ pulse at subjective night - No flowering
Long:
- Short day - No flowering
- Long day - Flowering
- Short day w/ pulse at subjective night - Flowering
** Assumes it’s a long day if light pulse at night bcuz they don’t expect light at that time on a short day
Effect of daily light period on flower formation w/ diff temperatures (28°C and 18°C)
- Most flowering between 8-10 hrs of light in both
- Overall more flowering at higher temp but same pattern in both (temp compensated, but not temp independent)
What hormone functions as part of the transducing mechanism for photoperiodic time measurement?
Melatonin (nocturnal hormone)
Melatonin peak when night is short vs long (in humans)
Short night - Narrow peak (inhibited by light)
Long night - Broad peak
Evidence for melatonin as transducing mechanism for photoperiodic time measurement? (3)
1) Pinealectomy eliminates circannual rhythmicity
- Prevents melatonin output (Behav continues but at lower amount)
2) Melatonin affects rhythm generation by the SCN
- W/out SCN -> Lost inhibition causes constant melatonin and lost rhythm
3) Melatonin syncs rhythms in pups
- PM melatonin and AM melatonin mother still had diff cycles than pups
- All pups had diff cycles and got weaned on day 24
Interaction between melatonin-regulated timer cells and prolactin-secreting cells in Soay sheep as pacemaker-slave timer system
- Winter vs Summer
Winter: More melatonin
- Melatonin is covering is covering peak of prolactin
Summer: Less melatonin
- Peak of prolactin is not under melatonin
