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What is an Endogenous Clock?

A biological timing mechanism with a built in schedule
Acts independently of cues in surroundings
Allows priorities to change over time


What is an Environmental Stimulus?

Feedback from surroundings to change priorities


What were the two hypothesis about crickets calling at the same time each day?

1) Cricket has an internal timer which can determine duration since last bout of calling
2) Nervous system set to initiate calling when light levels fall below a certain level


How were the two hypothesis about crickets calling at the same time each day tested?

1) Crickets kept under fixed light and temperature conditions for a number of days
2) Crickets kept under 12/12hr light/dark cycle


What was the conclusion about male cricket calling?

Environment independent endogenous clock, if they are removed from the usual light dark cycle they still call but it isn't set at 24 hours
The environmental stimulus synchronizes endogenous clock with local conditions


Describe environment independent behavioural cycle in mice.

Mice are nocturnal, odour cues are incredibly important for communication and avoiding location of predators. Olfactory bulb exhibits cyclical changes, mice are more sensitive to odours at night


What is melatonin?

It is a mammalian hormone that is secreted by the pineal gland
It is produced at night, modulates circadian timings, modulates sleep
Seasonal changes influence secretion and can interact with other reproductive hormones to influence breeding


How is melatonin production modulated?

Melatonin production is also modulated by external stimuli
If it is dark, photoreceptors in the eye are stimulated and this helps modulate the internal clock and more melatonin is produced
However if there is constant daylight or lots of artificial light, this inhibits production


Name 3 organisms lacking circadian rhythm.

Naked mole rats: Live underground, almost never surface
Nurse honey bees: Never leave hive, brain lacks gene expression associated with bee circadian clock
Forager honey bees: Collect pollen during the day brain exhibits signs of gene activity linked to circadian clock


Why is circannual rythm difficult to study?

2 year minimum period


Name 5 predictable environmental cues.

Tidal cycles
Lunar cycles
Change in day length
Sunrise / Sunset


What organism responds to the environmental cue, Tidal cycles?

Atlantic marsh fiddler crabs
*Plug burrows with mud HIGH
*Forage / look for mates LOW


What organism responds to the environmental cue, Onset of rainy season?

European Stonechats
*Abundance insects
*Mating so nestlings have sufficient food


What organism responds to the environmental cue, Sunrise / Sunset?

Males call to locate mate


What organism responds to the environmental cue, Change in day length?



What organism responds to the environmental cue, Lunar cycles?

Banner tail kangaroo rat
*More likely to stay underground with increased moonlight
*Aid to predators


Who studied seasonal changes in behaviour of European stonechats?

Holt et al 2009


What were the findings of Holt et al's 2009 study on European stonechats?

This annual cycle was still present even with no wild external stimuli
However after a period of time it became out of sync with wild counterparts (shortening)


Describe Holt et al's 2009 study on European stonechats?

European stonechats were taken from Kenya and moved to a lab in Germany
These birds were really young so had no experience of the spring/rainy season
The Stonechats were held in constant temperature & light conditions in the lab


Why is the rainy season an important cue for European stonechats?

When food is most abundant, the birds must reproduce.
Immediately prior to breeding the testicular width of these birds increases


Who studied social conditions in mice?

Mak et al 2007


What did Mak et al 2007 find?

Prior exposure to a subordinate: female spends equal time sniffing sub and dom male
Prior exposure to a dominant: increased time near the dominant
Exposure to dominant scent promotes neuronal growth to allow identification of dominant male should one be there


What are hormonal mechanisms?

Hormones play a key role in linking environmental information with rapid changes in behaviour.
Hormones, during development, can alter the nervous system & change physiology & behaviour.


Describe hormones and mouse infanticide.

Switch from infanticidal to paternal in 3 weeks
Endogenous clock – number of days since last copulation
Number of light: Dark cycles controlled infanticidal behaviour
Physiological mediator that links change in daylight to change in aggression:
Immediate but temporary effect
A) testosterone – linked with male aggression
B) Progesterone – suppresses parental behaviour in female rodents
KO mice produces lacking progesterone receptors
*KO – never attacked pups
*WT - >50% attacked
NSD in levels of circulating testosterone or progesterone in groups


Who studied hormones and mouse infanticide?

Schneider et al 2003