Biological Clocks Flashcards
biological clocks
internal mechanism in organisms that controls the periodicity of various function or activities, of time-keeping (typically biochemical)
rhythms & cycles; evidence points to brain as “master” clock center, but organs can have own clocks + unicellular can have clocks
History of our Understanding of Biological Clocks
400 BC: Androsenthes notices opening/closing leaves depending on time of day
1950: Starlings use Sun to migrate (internal clock to reorient)
1971: First clock gene (per) identified in fruit flies
1978: First clock-controlling gene (frq) discovered in red bread mold
1997: First clock gene found in mammals (mouse)
2001: First human clock gene discovered
Echinopsis chiloensis
nectar volume volumes vary in cycles throughout day
Biological clock in Honeybees (Germany)
bees trained to go to sugar bowl –> test again in US (when do they go?) –> depart 24 hours after og time in Germany
Weird Cycles in the Human Body
1 AM: pregnant women most likely to go into labor (older times –> groups of people less likely to migrate around)
6 AM: melatonin levels begin to fall (wake up normally)
8 AM: calories burned most efficiently (about to become active for diurnal species)
Advantages to Biological Clocks
- permits animal to “anticipate” env. change (fiddler crab + incoming tide)
- behavior timing with event that cannot be sensed directly (bees visiting flowers distant from hive)
- continuous measurements of time (change in bee dance as sun moves)
Characteristics of Clocks
- cycles continue in absence of “obvious” env. cues (light, temperature)
- cycles are stable and quite precise (but not perfect)
What governs clocks?
- Early Controversies (mid 1970s) - internal vs. external regulation; endogenous vs. exogenous
- “Zeitgeber” (time-setter): external cues “entrainment” (setting the clock)
Golden-mantled ground squirrel hibernation (Pengelley)
- Winter –> metabolism + body temp decrease
- Spring –> metabolism + body temp increase
- squirrels raised in lab still able to hibernate at right time of year
evidence for endogenous rhythms?
Cricket song
evidence for exogenous rhythms (need sunlight to maintain) and the zeitgeber
loss of rhythm in cricket if lobes disconnected from rest of brain
Biological clock model
Environmental cues (zeitgeber) —> Clock-setting pathway (Sensory receptors —> Pacemaker (clock mechanism, regulatory)) —> Observed rhythms (locomotory, feeding, hormone release, etc)
Biological clocks
Circadian rhythms (24 hour)
Circannual rhythms (1 year)
persist under lab conditions (often some drift) (ex. hamster in wheel under constant dim light —> lack light —> starts activity 12 min later each day)
“free-running” cycle
does not correspond to usual cycle in nature
ex. hamster wheel
Biological clocks classification by cycle length
* Daily (nocturnal vs. diurnal activity patterns) (ex. honeybee feeding at flowers)
- Tidal (ex. fiddler crabs returning to burrows before tide)
- Monthly - Lunar (reproductive cycles) (ex. ant lion construction of pit fall trap for capturing prey (larger during full moon)
- **Annual **(bird migration)
Seashores and fiddler crabs
Relevant “day” is lunar day (24.8 hour interval between successive moonrises)
Crabs active at low tide (not “free-running”
