Assessment and Adaptive Behavioral Plasticity

A remarkable aspect of behavioral plasticity is that it is very often adaptively appropriate. A large literature on ethology and animal behavior could be cited documenting how observed changes in behavior either have a demonstrable functional role that is known or is likely to enhance the performer's survival or reproductive success. Animals regularly adjust their behavior to their own

Figure 2 Condition-sensitive performance (plasticity) in behavioral traits. Modified from West-Eberhard MJ (2003) Developmental Plasticity and Evolution. New York: Oxford University Press, after Otte D (1972) Simple versus elaborate behavior in grasshoppers. Analysis of communication in the genus Syrbula. Behaviour 42: 291-322.

Figure 2 Condition-sensitive performance (plasticity) in behavioral traits. Modified from West-Eberhard MJ (2003) Developmental Plasticity and Evolution. New York: Oxford University Press, after Otte D (1972) Simple versus elaborate behavior in grasshoppers. Analysis of communication in the genus Syrbula. Behaviour 42: 291-322.

Encoptolophus

Spharagemon

Trimerotropis pallidipennis

Arphia and Pardalophora subgracilis costalis (Colorado) costalis (Texas)

equale crepitans

A. xanthoptera A. sulphurea

P. phoenicoptera P. apiculata

A. pecos P. haldemani

J

Ordinary stridulation J^

III

111 Femur shaking

Vibratory stridulation J^

Vibratory stridulation (bursts)

J3

Ticking J^

Figure 3 Recombination of modular behavioral units in the evolution of communication in grasshoppers. The same five pattern elements (box) recur in different combinations in five genera of grasshoppers. The hierarchical structure of modular behavioral traits is evident: some pattern elements have repeated modular subcomponents; and several pattern elements can compose the species-characteristic song. The structural transitions indicated by arrows do not necessarily represent phylogenetic relationships within the genera. From West-Eberhard MJ (2003) Developmental Plasticity and Evolution. New York: Oxford University Press, courtesy of Dan Otte.

advantage. They seem to evaluate or assess conditions, and then behave accordingly.

Demonstration of the adaptiveness of plastic traits requires satisfying stringent criteria. In some cases, a hypothesis that observed behavioral plasticity is adaptive is relatively easy to support. The response of a hermit crab to disturbance, for example, is to withdraw into its shell. Such ensconcement behavior is highly likely to have evolved as an adaptive response: ensconcement upon disturbance supports the hypothesis that the shell has a protective function; yet ensconcement is a costly response because while inside its shell the crab cannot feed or interact with other crabs. The condition-sensitive (plastic) 'reversibility' of ensconcement can safely be assumed to be selectively advantageous, and natural selection is expected to adjust the timing and duration of the ensconcement response.

Experimental demonstrations of adaptive behavioral plasticity that involves environmental assessment in many different animals and contexts are among the outstanding achievements of behavioral ecology during recent decades. Examples include analyses of conditions required for the decision between different alternative mating tactics of males; of relatedness involved in decision of whether to help or not to help conspecific reproductives; of dominance and subordinance of competitors; of the costs and values of different food sources; and of places to live.

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