Meeting Abstract
The influence of a single hormone on expression of two or more performance or life history traits may constrain or facilitate the evolution of these traits. Two hypotheses have been proposed to explain whether such hormonal pleiotropy affects trait evolution. One hypothesis proposes that the different parts of an endocrine axis (hormone titer, receptor expression, etc.) are independent from one another and therefore two traits that are both affected by the same hormone can evolve separately. For example, one trait could be influenced by modifying its sensitivity to the signal whereas the expression of the other trait could be influenced by signal intensity. A second hypothesis proposes that the features of an endocrine axis are not independent from one another such that the expression of two phenotypic traits affected by the same hormone are yoked. One way to test these hypotheses is to study the mechanistic causes of variation in these traits, such as asking whether hormone titers or receptor expression explains more variation in the trait. We will discuss an alternative approach using quantitative genetics that may be useful for longitudinal studies of wild animals. We extend these hypotheses by developing a model to derive predictions about the conditions under which hormonal pleiotropy would constrain the independent of phenotypic traits. We focus on performance and life history traits and how the effects of hormonal pleiotropy on the evolution of these traits depends upon the genetic correlations between the hormone and traits as well as the direction and strength of selection on the two traits. Finally, we discuss methodological aspects of this approach and review the literature for examples that have estimated these model parameters to characterize the studies that have or have not found support for these model predictions.
