TIMING RESPONSES Continued…

COMPOUND RHYTHMS  The environment changes most on a shoreline because the cycle of day and night occurs as well as the tidal change.

COMPOUND RHYTHMS  The environment changes most on a shoreline because the cycle of day and night occurs as well as the tidal change. Eg – Sandhoppers show a rhythm of both daily and tidal components = they emerge at night to forage for food but also only at low tide.

INTERNAL AND EXTERNAL TIMING  Internal / endogenous rhythms

INTERNAL AND EXTERNAL TIMING  Internal / endogenous rhythms  Involve an internal clock – independent of changes in the external environment but set by the environment.

INTERNAL AND EXTERNAL TIMING  Internal / endogenous rhythms  Involve an internal clock – independent of changes in the external environment.  External / exogenous

INTERNAL AND EXTERNAL TIMING  Internal / endogenous rhythms  Involve an internal clock – independent of changes in the external environment.  External / exogenous  Few examples of this – seasonal change in the growth rates of plants = produces variation in the food supply for animals which in turn governs seasonal fluctuations in populations.

EVIDENCE FOR INTERNAL CLOCKS  Some plants (Oxalis) show daily sleep movements – even when in constant light.

EVIDENCE FOR INTERNAL CLOCKS  Some plants (Oxalis) show daily sleep movements – even when in constant light.  When the period of time does not correspond exactly with the period of the environmental cue = ‘free running’

EXAMPLE…  Bees can be trained to feed at a certain time. In Paris the bees fed between 8pm and 10pm. When transferred to New York, they kept feeding at Paris time SHOWING THAT FEEDING IS NOT DETERMINED BY AN ENVIRONMENTAL RHYTHM.

CIRCADIAN RHYTHMS  Circa – ‘about’ Dian ‘day’  Free-running endogenous rhythms don’t usually coincide with those of the environment – internal clock must be constantly ‘reset’ or entrained by the environment.

CIRCADIAN RHYTHMS  Circa – ‘about’ Dian ‘day’  Free-running endogenous rhythms don’t usually coincide with those of the environment – internal clock must be constantly ‘reset’ or entrained by the environment.  The enviro cue to set the clock is called the zeitgeber (German for time giver) and with circadian = common is sunrise or sunset.

CIRCADIAN RHYTHMS  Circa – ‘about’ Dian ‘day’  Free-running endogenous rhythms don’t usually coincide with those of the environment – internal clock must be constantly ‘reset’ or entrained by the environment.  The enviro cue to set the clock is called the zeitgeber (German for time giver) and with circadian = common is sunrise or sunset.  This entrainment is important – animals can adjust to seasonal change in time of dawn/dusk. - also allows migratory animals that make considerable east-west movements adjust their clocks.

FREE RUNNING Free running is a term used to describe a circadian rhythm that is not entrained to any kind of external time cues, such as the natural dark-light cycle.circadian rhythmentrained

PHASE SHIFTING  The time of the peaks of an endogenous rhythm are advanced or slowed down.

PHASE SHIFTING  The time of the peaks of an endogenous rhythm are advanced or slowed down.  Often it can be light or temperature (reptiles rely on external heat for warmth), food or social factors.

TIME SENSE THROUGHOUT THE DAY  Internal clock can be used to determine the time of day

TIME SENSE THROUGHOUT THE DAY  Internal clock can be used to determine the time of day  Eg – bees visit flowers during the periods when there is nectar as if they ‘consulted’ their internal clock to ‘know the best time of day’. A bee can be trained to visit several artificial sources and the bees have no trouble keeping their ‘appointments’ provided the food source is kept to the same timing as their own – 24 hours.

TIME SENSE THROUGHOUT THE DAY  Internal clock can be used to determine the time of day  Eg – bees visit flowers during the periods when there is nectar as if they ‘consulted’ their internal clock to ‘know the best time of day’. A bee can be trained to visit several artificial sources and the bees have no trouble keeping their ‘appointments’ provided the food source is kept to the same timing as their own – 24 hours.  Birds adjusts it’s angle to the sun in order to continue flying in the correct direction.

BIOLOGICAL SIGNIFICANCE  A internal clock enables an organism to anticipate the environmental changes – more time and energy devoted the feed and reproduce.

LOCATION OF THE CLOCKS (OSCILLATION)  The control of circadian rhythms – hypothalamus. Supra-chiasmatic nuclei (SCN). When SCN of rats are removed, all rhythmic activity stops.

LOCATION OF THE CLOCKS (OSCILLATION)  The control of circadian rhythms – hypothalamus. Supra-chiasmatic nuclei (SCN). When SCN of rats are removed, all rhythmic activity stops.  Birds – clock is located in pineal gland in the brain. If removed, rhythms stop. If put in, the bird has rhythms of the implant.

LOCATION OF THE CLOCKS (OSCILLATION)  The control of circadian rhythms – hypothalamus. Supra-chiasmatic nuclei (SCN). When SCN of rats are removed, all rhythmic activity stops.  Birds – clock is located in pineal gland in the brain. If removed, rhythms stop. If put in, the bird has rhythms of the implant.  Insects – ‘probably’ located in the optic lobes of the brain.

MECHANISM OF ENTRAINMENT – 3 PROCESSES  Detection of external rhythm using some form of zeitgeber (eg light)

MECHANISM OF ENTRAINMENT – 3 PROCESSES  Detection of external rhythm using some form of zeitgeber (eg light)  Transmission of a signal from the receptor (eg eyes) to the clock mechanism

MECHANISM OF ENTRAINMENT – 3 PROCESSES  Detection of external rhythm using some form of zeitgeber (eg light)  Transmission of a signal from the receptor (eg eyes) to the clock mechanism  A change in the phase of the clock.

TEMPERATURE COMPENSATION  Biological clocks are not affected by the change in ambient temperature.

TEMPERATURE COMPENSATION  Biological clocks are not affected by the change in ambient temperature.  It can alter them in other ways however: -Temp can act as a zeitgeber -Exposure to abnormally low temps usually causes the clock to stop