PRESTON, KATHERINE A. Dept. of Biological Sciences, Stanford University, Stanford, CA 94305. - __Plasticity in integrated phenotypes: a conceptual overview.__

In most ecological and comparative studies, phenotypic integration is
inferred from phenotypic correlations. Four main elements characterize
phenotypic correlation: 1.strength (correlation coefficient), which is
the most common measure of integration; the form of the relationship
between trait pairs, including 2.the intercept and 3.the slope
(scaling coefficient); and 4. the pattern of correlation across
environments (plasticity integration). These elements may vary
somewhat independently. For example, it is not necessary for traits to
show correlated plasticity in order to remain strongly correlated in
different environments. If there is correlated plasticity and two
traits respond proportionally, then there will be no change in either
the strength of the correlation or the form of the relationship
between them. By contrast, if traits change in a coordinated fashion
but disproportionately relative to one another, then the scaling
relationship between them will change, reflecting a change in their
functional relationship. Thus traits may show a consistent pattern of
integration in various environments, while the forms of the pairwise
relationships and the degree of plasticity integration varies.
Although plasticity integration is not necessary to maintain
phenotypic integration across environments, plasticity integration
makes consistent patterns of integration more likely. Analyzing the
combination of changes in correlation strength and form across
environments, and the degree of plasticity integration, may provide
insight into mechanisms underlying phenotypic integration and the
potential for integration to constrain the evolution of adaptive
plasticity in integrated traits.
**Key words:** constraint, correlation, functional relationship, phenotypic integration, plasticity, scaling