A level Biology exam revision resources written by A level Examiners


Organisms sometimes show specific behaviour patterns before mating. These have the following advantages.

  • They allow the attraction of a mate, possibly from a considerable distance e.g. some moths release chemical attractants (pheromones) which can be detected several kilometres away.
  • They allow species recognition, and ensure mating is with individuals of the same species.
  • They allow sex recognition. Some species do not show clear differences between sexes, and different patterns of behaviour can help distinguish the sexes.
  • They can stimulate sexual behaviour in the other sex, or stimulate egg production.
  • They allow recognition of sexually mature / receptive individuals.
  • They can enable choice of fittest individuals - those that are likely to have a good set of alleles.

Pheromones are chemicals released by an organism into its environment, enabling it to communicate with other members of its own species. They are often released at times when individuals are sexually mature, and recapture to mating. They are often chemically volatile molecules, which enables them to evaporate from surfaces, and be carried in air currents.

Sometimes the courtship behaviour in one sex is triggered by a visual cue provided by the opposite sex. We call these visual cues sign stimuli and the response is the result of the sign stimuli triggering an innate releaser mechanism which causes the response behaviour. The innate releaser mechanism is an unconscious response, eg in sticklebacks the male responds to the red belly of a female, carrying eggs, with a zig-zag dance. This behaviour can be triggered by any bright red object.

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