Androgen receptors and muscle: a key mechanism underlying life history trade-offs.

Sexual dimorphism in skeletal muscle is prominent in mammals, with males typically having larger and stronger muscles than females. Furthermore, neuromuscular systems with sexual functions are remarkably sexually dimorphic in a wide variety of vertebrates. Endocrine mechanisms are of central importance for sexual differentiation of these traits, and anabolic actions of gonadal testosterone have been intensively studied. Here we review the relationship between androgen receptor (AR) and sexual differentiation of neuromuscular systems. We focus our review on the hypotheses that sexual dimorphism and androgen responsiveness of neuromuscular systems is a function of the amount of AR expressed by muscle and that AR in muscle is a key mechanism on which evolution acts to shape individual and species differences in reproductive behavior.