Measures of fitness effects (current adaptation) are just one part of the evolutionary explanation of behavioral plasticity. Another asks where novel plastic behaviors come from, and attempt to trace the phenotype transitions that give rise to novelties, beginning with some ancestral state when the trait did not exist in its observed form. Such studies may examine how the trait maps onto a phylogeny ofrelated species, and may involve 'phenoty-pic engineering', the manipulation of hypothesized ancestral states with hormones or altered environmental conditions to explore the mechanisms and circumstances that may have produced novel behavioral variants that were material for selection when the trait originated.
When a novel input - a mutation or an environmental factor - affects the responsive phenotype to stimulate a novel behavior, the behavior immediately and simultaneously manifests both a new form and a regulatory mechanistic basis. These are not independently originating traits, but they are semi-independently subject to sordidus collare saxatile humile bolli maritima californica evolution under selection, with the form (structure, efficiency) and the regulation (threshold or liability for expression) being different modular aspects of the pheno-type. Most behavioral traits are likely to be genetically variable from the beginning, due to genetic variation in the responding structures (nerves, appendages, muscles) that produce them. So there is a potential for the genetic accommodation of recurrently induced novel traits -evolutionary genetic change under natural selection on their regulation and form.
Some behavioral alternatives are 'antagonistic' in that they are performed in 'opposite' situations: the act or its performer observed in one situation would do poorly in the other. Some evolutionary genetic models treat performance in two different environments as two characters and conclude that a negative genetic correlation between them would limit the evolutionary prospects of both. But 'conditional' expression of behaviors, for example, those associated with alternative tactics of mating or feeding behavior and related morphology, liberates them from such constraints by limiting expression of genes, or use of gene products, to the situations where they are advantageous. This is one way in which the often finely tuned adaptive plasticity of behavior can facilitate evolution.
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