Biological rhythms

Question 1

What are biological rhythms?

Answer 1

Rhythms that occur when an animal’s
-physiological activities and
-behaviour patterns
can be directly related to environmental features that occur with regular frequency

Question 2

Name the three types of rhythm

Answer 2

-Circadian: day
-Circannual: year
-Circalunar: month

Question 3

Tidal rhythms are seen in which animal?

Answer 3

Shore crab- active at high tide

Question 4

Circalunar rhythms are seen in which animals?

Answer 4

Nocturnal predators e.g., antlions

Question 5

How do animals synchronise their behaviour and physiology to cyclic changes in the external environment?

Answer 5

• They have a direct response to changes in external environment
• Biological clock (endogenous rhythm) is used to synchronised to changes in external environment
• A combination of both

Question 6

What is the first piece of evidence for the existence of biological clocks?

Answer 6

Rhythm persists in constant conditions of light, temperature, etc
- Seen in flying squirrel which is nocturnal and maintain 24-hour activity pattern even in constant darkness

Question 7

What is the evidence for the existence of biological clocks in rats?

Answer 7

Cyclic self- stimulation of the pleasure
centre in rats is maintained

Question 8

What is the evidence for the existence of biological clocks in ground squirrel?

Answer 8

Circannual hibernation cycle of ground
squirrel maintained in constant conditions

Question 9

What is the second piece of evidence for the existence of biological clocks?

Answer 9

Animals reared in isolation exhibit rhythms
- e.g., Lizards hatched from eggs & reared under different light regimes all had same rhythm period (about 24h)

Question 10

What is the third piece of evidence for the existence of biological clocks?

Answer 10

Mutants with altered rhythm
- e.g., mutant mice with free-running period of 25 h.
normal mice <24 h

Question 11

What are the characteristics of endogenous rhythms?

Answer 11

• Persist in absence of environmental cues
• Period is not exactly that of environmental cycle
• Rhythm is entrained (reset) by environmental cues (zeitgebers), especially light
• Temperature compensation:
  rhythm persists despite variation in environmental temperature

Question 12

What are the adaptions of biological clocks?

Answer 12

1. Synchronise the activities of animals with conditions in
   their environments, including their social environments
2. Enabling them to prepare in advance for predictable
   events such as
   – night
   – winter
   – reproductive condition in potential mates

Question 13

What is the circadian rhythm entrained by?

Answer 13

Daylight

Question 14

What conditions do circadian rhythms persist in?

Answer 14

In constant conditions where the free running period is just under or just over 24 hours and is controlled by an endogenous circadian clock

Question 15

What animals are diurnal (active during day)?

Answer 15

Humans, mammals and birds

Question 16

What species are crepuscular (active at dawn/dusk)?

Answer 16

Mice and rats

Question 17

Where is the master clock located?

Answer 17

In the brain
-It is in the suprachiasmatic nucleus (SCN) of the hypothalamus

Question 18

What is the master clock influenced by?

Answer 18

By light which is perceived by the retina

Question 19

What tract is light directly transmitted along?

Answer 19

Retino-hypothalamic tract

Question 20

What is the role of the pineal gland?

Answer 20

It regulates the production and release of the hormone melatonin which affects activities including sleep

Question 21

What hormone regulates the circadian rhythm?

Answer 21

Melatonin

Question 22

What do chronotypes impact?

Answer 22

• Athletic performance
• Personality traits underlying behavioural and emotional problems
• Risk taking propensity
• Morality

Question 23

Why have circannual rhythms evolved in animals?

Answer 23

Evolved to coincide with environmental conditions and food availability both for itself and its offspring

Question 24

Circannual rhythms cause changes in what?

Answer 24

Seasonal changes in body weight, gonad size, moulting, restlessness (migratory species), food

Question 25

What was observed by Zeitgebers experiment?

Answer 25

– Photoperiod (daylight length) is the most important especially at higher latitudes
– Rain may be important in tropics
– Temperature may be zeitgeber for hibernation

Question 26

Circannual cycle in Palolo worms

Answer 26

• Breed during neap tides of last quarter