Meeting Abstract

S3.3  Sunday, Jan. 4  Phenotypic Integration and Independence: Hormones, Performance, and Response to Environmental Change KETTERSON, E.D.*; ATWELL, J.W; Indiana Univ.; Indiana Univ. ketterso@indiana.edu

The concepts of hormonal pleiotropy, physiological epistasis, and hormonal correlations raise many unanswered questions with respect to the links between hormones and whole-animal performance. One such question is the functional importance of hormonal correlations between the sexes and whether they might serve to constrain the evolution of sexual dimorphism. Another such question is the nature of individual variation in hormonal systems and how that variation relates to phenotypic evolution. Hormonally mediated characters can evolve owing to changes in hormone secretion, hormonal affinity for carrier proteins, rates of degradation and conversion, and interaction with target tissues. Critically, we know very little about whether these changes occur independently or in tandem, and thus whether hormones promote phenotypic integration or allow for phenotypic independence. Thus, when a population encounters a new environment that leads to altered expression of hormonally mediated characters, is that alteration likely to have come about through changes in hormone secretion (signal strength) or changes in response to a fixed level of secretion (target tissue sensitivity) or both? If the phenotype is tightly integrated and only the signal responds, adaptive modification may be limited by past selection for phenotypic integration. If individual target tissues readily unplug from a hormone signal in response to selection, then the phenotype may be seen as a loose confederation that responds on a trait-by-trait basis, readily allowing adaptive modification. Studies reviewed here and questions for future research will address the relative importance of integration and independence by comparing sexes, individuals, and populations.