CIRCANNUAL RHYTHMS

Question 1

Seasonal timing of life history events such as ____, ____, _____ have evolved in many animals to coincide with ______ _____ and ______ _____ both for itself and its offspring.

Answer 1

reproduction, migration and hibernation; environmental conditions and
food availability

Question 2

May be marked seasonal changes in

Answer 2

body weight, gonad size, (migratory species); moulting,
restlessness, food preferences

Question 3

How are annual cycles controlled?

Answer 3

• There is some evidence for the existence of a circannual clock, but the mechanism is not
  well understood
• Photoperiod (daylight length) is an important environmental cue (zeitgeber) especially at
  higher latitudes; The amount of daylight in a 24h period measured. This depends on the
  circadian clock
• Rain may be important in tropics;
• Temperature may be a zeitgeber for hibernation

Question 4

Example

Answer 4

Palolo worms breed at sunrise on the last day of the last quarter of the moon in October,
November and December (even when kept in the lab). Circalunar rhythms are important in
the timing of spawning. This synchronisation swamps predators.