recap

52.5 recap

Biological rhythms allow an animal to anticipate changes in its environment. In mammals, a circadian clock located in the suprachiasmatic nuclei generates a rhythm that is entrainable by environmental information. The navigational abilities of animals range from simple piloting by landmarks to distance–direction and bicoordinate navigation. Behaviors may evolve into communication signals if the transmission of information benefits both the sender and the receiver.

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learning outcomes

You should be able to:

  • Describe characteristics of circadian rhythms.

  • Explain the concept of a time-compensated solar compass.

  • Describe the different forms of animal communication and their advantages and disadvantages.

  • Evaluate the effectiveness of various forms of animal communication in specific circumstances.

1.

What is a free-running circadian rhythm, and how is it entrained by light to the 24-hour day?

A free-running circadian rhythm is one that is not entrained to a regularly occurring signal, such as sunrise and sunset, but is expressing an endogenous periodicity. When a time cue such as a regular light−dark cycle is imposed on a free-running rhythm, that cue will either phase advance or phase delay the circadian clock to bring it into phase with the environmental light−dark cycle.

2.

Why is it important for honey bees to have a time-compensated solar compass, and how does that mechanism influence the waggle dance?

The direction to the sun can be used to tell compass directions if you know the time of day. A time-compensated solar compass uses an endogenous timing mechanism to compensate for the movement of the sun’s position in the sky. Thus, if a honey bee finds food to the south at noon, its waggle dance on the honeycomb in the hive will be straight up, but as time passes into the afternoon, the direction of the waggle dance will have to be more and more to the left of straight-up to indicate that the direction to the food source is south.

3.

Which forms of communication are most efficient for inter-individual communication and for broader population-level communication? Explain your answer.

The most efficient forms of inter-individual communication are tactile communication, which can be highly specific to the individual, and visual communication, which can convey considerable specific information in a very short time to an individual that is focused on the sender. Sound is an efficient form of communication for a broader population because it permeates the whole environment. Olfaction can be good for either individual or for population communication, depending on the volatility of the odorant.

When behaviors involve interactions between multiple individuals, we have to consider how natural selection operates on all of the interacting parties, whether they are sending signals or receiving them. This concern becomes particularly relevant in the case of social behaviors.