Sensory Receptors

Actors use specially designed signals to modify the behavior of reactors (e.g. snapping turtle lure, coordination of hunting movements). Ritualization: the process by which a functional behavior pattern or structure is transformed into a communication signal. Evolution shapes mechanisms for information transfer towards increased signal/noise ratio. Towards this goal, displays become more conspicuous through exaggeration of movements, components become simplified, movements are "frozen" into postures, behaviors are stereotyped, and additional body structures may evolve for increased effect.

Ritualized displays may arise from: Intention movements: behavior patterns that precede or prepare for other behaviors; Displacement activity: behavior patterns seemingly unrelated to the behavioral context in which it occurs. Displays generally prove of advantage to both signaller and receiver. A particular behavior proves of predictive value for bystanders. Evolution provides receiver with "knowledge" about this association, leading to adjustment of own behavior. If this adjustement proves advantageous to sender then it further encourages this process through ritualizing the signal. Signal and response coevolve.

Generally interests of signaler and receiver coincide, however, differences with regard to Conflict vs. Cooperation: If signaler seeks to manipulate receiver --> "coevolutionary arms race". Cooperation of signaler and receiver lead to heightened receiver sensitivity and reduction in signal amplitude --> "conspiratorial whispers". Necessity for honesty of signalling in conflict: Zahavi's handicap principle: "Crests and horns, as well as facial decorations such as eye lines, help their bearers display at a distance the direction of their gaze. But by displaying the direction of their attention, they also provide information as to which directions they are not observing. This information endangers individuals of a low quality more than it endangers dominants or high quality individuals. A strong individual, sure of itself and of its dominance over its neighbors, does not fear a surprise attack from behind, and thus loses little from disclosing the direction it is not facing, while a weak individual cannot afford such a handicap" -- Zahavi, A. (1993) The fallacy of conventional signalling. Phil. Trans. R. Soc. Lond. B. 340:227-230

Cheat-proof signals:

• Signallers of different qualities send different signals
• Signals are costly
• Signals cost more for signallers of lower quality

  Waggle dance of bees © unknown

  . Bees use signs to convey information about available food sources. Returning successful foragers perform a series of movements which indicate direction and distance to the flowers. Round dance indicates a source close by. Operational information is contained in the flower scent adhering to the dancing animal. More distant sources are indicated by a flat figure of eight dance which conveys direction and distance.

Reading Assignment

• Chapter 7: The Nervous System and Behavior.

Food for Thought

• How much of our behavior is driven by external events? How much of our behavior is a simple response to stimuli?

Links of interest

• Human hearing
• Walter Heiligenberg's work in electric communication
• A summary of the visual system
• Mark Konishi - auditory sensory map in prey-capture of Owls
• Animal Sound Sites
• Library of natural sounds