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Biological Clocks Free-running endogenous clock. Can be entrained by external cues.

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Presentation on theme: "Biological Clocks Free-running endogenous clock. Can be entrained by external cues."— Presentation transcript:

1 Biological Clocks Free-running endogenous clock. Can be entrained by external cues

2 Selective advantage Hypothesis 1: biological clocks control behaviours where some synchronisation is necessary eg1 intraspecific (for breeding or migration) eg2 interspecific (to exploit a seasonal food source) Hypothesis 2: physiological preparation for an anticipated environmental change eg storing food reserves prior to hibernation, which is more energy efficient.

3 Timing Need to know time for navigation Day-length - internal clock Need to “date” for migration 3 Wilson’s Plover

4 Free-running Rhythms Generally have a slightly longer period than that of the environmental rhythm they are associated with. Rhythm is entrained or synchronized to the environmental cue (zeitgeber). May involve a phase-shift if the environmental pattern is changed e.g. jet lag is the body’s slow altering of the circadian rhythm to fit the new cycle.

5 Biological Timing Responses Governed by internal clocks  Annual cycles  Daily cycles  Lunar cycles NOT necessarily governed by environment:  organisms can anticipate changes  cycles continue in constant lab conditions

6 Geophysical cycle length of cycle biological rhythm known zeitgebers solar year365.2 dayscircannualphotoperiod lunar month29.5 dayscircamonthlylight of full moon solar day24 hourscircadianlight, temp., humidity tidal12.4 hourscircatidaltidal activity

7 Biological clock – internal Period of rhythm – length of cycle Phase shift – change in onset of period Free-running period – independent of external cues Entrainment – regular resetting of clock (zeitgeber) Zeitgeber (time giver) – environmental cue to reset clock Circa (about) – cycles not in synch with cues Photoperiod – responses to length of day / night Exogenous rhythm – controlled by external cues Endogenous rhythm – controlled by internal clock

8 Biological Clocks Endogenous, free-running May use exogenous cues to reset clock May predict onset of periodic change Cycle often longer than associated exogenous cycle Entrained by exposure to external cues. May involve chemical signals. May involve a phase-shift e.g. jet lag

9 Biological clocks used for: Control daily rhythms – sleep, pulse, blood pressure, temperature, sex drive..... Reproduction timing – coordinate courtship rituals, release of sperm and eggs into water, sexual preparedness Migration preparedness – eating lots Winter preparedness – storing food, coat thickness, hibernation Navigation – solar & stellar

10 Biological Rhythms Daily Rhythms Daily Rhythms – patterns of behaviour linked to the day-night cycle nocturnal = night-active e.g. possums diurnal = day-active e.g. bees crepuscular = active in twilight (dawn and dusk) e.g. rabbits Annual Rhythms Annual Rhythms – linked to Earth rotation around the sun and seasonal changes due to Earth’s axial tilt (such as photoperiod) e.g. change in coat colour of Arctic fox Tidal Rhythms Tidal Rhythms – patterns of behaviour linked to the tides, a result of the gravitational pull of the Moon and the Earth’s rotation e.g. mud crabs Lunar Rhythms Lunar Rhythms – (much less common) patterns of behaviour linked to the rotation of the Moon around the Earth e.g. Whitebait spawning

11 Geophysical Rhythms Biological rhythms mirror geophysical rhythms. ‘All living organisms are subjected to a diverse set of geophysical oscillations due to the ceaseless rotation of the moon round the earth, and the earth round the sun and on its own axis’ (D. S. Saunders, 1977).

12 Circadian rhythm De Mairan (1729) showed mimosa leaf movements – circadian rhythm - in absence of external cues.

13 Absence of rhythmic environments? Rhythmicity persists in animals in the absence of environmental cues. Eg organisms in deep sea, caves and polar regions.

14 Honey bees are chronobiological Very accurate time perception / time sense Clear circadian rhythms and memory. Exhibit distinct behaviours in their everyday life. Complex communication. Return from a good food source and perform a dance to communicate position of the food.

15 Testing internal clock hypothesis Timing controlled by internal biological clocks, which continue to function in the absence of external time cues.

16 Recording animal activity We expect to see a recognisable rhythm associated with a geophysical rhythm.

17 Location A Location B Location C Waggle dance (food distant) A C B


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