title: Evolutionary patterns of adaptive acrobatics and physical performance predict expression profiles of androgen receptor - but not oestrogen receptor - in the forelimb musculature.
abstract: 1. Superior physical competence is vital to the adaptive behavioral routines of many animals, particularly those that engage in elaborate socio-sexual displays. How such traits evolve across species remains unclear. 2. Recent work suggests that activation of sex steroid receptors in neuromuscular systems is necessary for the fine motor skills needed to execute physically elaborate displays. Thus, using passerine birds as models, we test whether interspecific variation in display complexity predicts species differences in the abundance of androgen and estrogen receptors (ARandERα) expressed in the forelimb musculature and spinal cord. 3. We find that small-scale evolutionary patterns in physical display complexity positively predict expression of theARin the main muscles that lift and retract the wings. No such relationship is detected in the spinal cord, and we do not find a correlation between display behavior and neuromuscular expression ofERα. Also, we find thatARexpression levels in different androgen targets throughout the body - namely the wing muscles, spinal cord, and testes - are not necessarily correlated, providing evidence that evolutionary forces may driveARexpression in a tissue-specific manner. 4. These results suggest co-evolution between the physical prowess necessary for display performance and levels ofARexpression in avian forelimb muscles. Moreover, this relationship appears to be specific to muscle andAR-mediated, but notERα-mediated, signaling. 5. Given that prior work suggests that activation of muscularARis a necessary component of physical display performance, our current data support the hypothesis that sexual selection shapes levels ofARexpressed in the forelimb skeletal muscles to help drive the evolution of adaptive motor abilities.
authors.affiliation: Department of Biology, Wake Forest University, 228 Winston Hall, Winston-Salem, NC 27109, USA ; Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, CA 90095, USA ; Laboratory of Neuroendocrinology, Brain Research Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Fuxjager
authors.affiliation: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Joy
authors.initials: J
authors.lastname: Eaton
authors.affiliation: Department of Biology, University of Mississippi, University, MS 38677, USA.
authors.forename: Willow R
authors.initials: WR
authors.lastname: Lindsay
authors.affiliation: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, CA 90095, USA ; Department of Behavioral Neurobiology, Max Planck Institute for Ornithology, Seewiesen, Germany.
authors.forename: Lucie H
authors.initials: LH
authors.lastname: Salwiczek
authors.affiliation: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Rensel
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Julia
authors.initials: J
authors.lastname: Barske
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
authors.forename: Laurie
authors.initials: L
authors.lastname: Sorenson
authors.affiliation: Department of Biology, University of Mississippi, University, MS 38677, USA.
authors.forename: Lainy B
authors.initials: LB
authors.lastname: Day
authors.affiliation: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, CA 90095, USA ; Laboratory of Neuroendocrinology, Brain Research Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA ; Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA 90095, USA ; Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Balboa, Ancón, Panama.
authors.forename: Barney A
authors.initials: BA
authors.lastname: Schlinger
keywords: manakins; neuromuscular physiology; sexual selection; social display; testosterone; tropical birds