Gonadotropin Hormone Modulation of Testosterone, Immune Function, Performance, and Behavioral Trade‐Offs among Male Morphs of the Lizard Uta stansburiana

Abstract

Sexual selection predicts that trade-offs maintain trait variation in alternative reproductive strategies. Experiments often focus on testosterone (T), but the gonadotropins follicle-stimulating hormone and luteinizing hormone may provide a clearer understanding of the pleiotropic relationships among traits. We assess the activational role of gonadotropins on T and corticosterone regulation in traits expressed by polymorphic male side-blotched lizards Uta stansburiana. Gonadotropins are found to enhance and suppress multiple physiological, morphological, and behavioral traits independently, as well as indirectly via T, and we demonstrate selective trade-offs between reproduction and survival. The OBY locus, a genetic marker in our model vertebrate mating system, allows characterization of the interaction between genotype and hormone treatment on male traits. Our results suggest that oo, ob, and bb males are near their physiological and behavioral capacity for reproductive success, whereas yy and by males are maintained below their physiological maximum. Both by and yy morphs show trait plasticity, and we demonstrate that gonadotropins are likely proximate effectors that govern not only trait differences between alternative mating strategies but also morph plasticity. Gonadotropins clearly represent an important mechanism maintaining variation in physiological, morphological, and behavioral traits, as well as potentially maintaining the immunosuppression costs of male sexual signals.