title: Sexual selection predicts brain structure in dragon lizards.
abstract: Phenotypic traits such as ornaments and armaments are generally shaped by sexual selection, which often favours larger and more elaborate males compared to females. But can sexual selection also influence the brain? Previous studies in vertebrates report contradictory results with no consistent pattern between variation in brain structure and the strength of sexual selection. We hypothesize that sexual selection will act in a consistent way on two vertebrate brain regions that directly regulate sexual behaviour: the medial preoptic nucleus (MPON) and the ventromedial hypothalamic nucleus (VMN). The MPON regulates male reproductive behaviour whereas the VMN regulates female reproductive behaviour and is also involved in male aggression. To test our hypothesis, we used high-resolution magnetic resonance imaging combined with traditional histology of brains in 14 dragon lizard species of the genus Ctenophorus that vary in the strength of precopulatory sexual selection. Males belonging to species that experience greater sexual selection had a larger MPON and a smaller VMN. Conversely, females did not show any patterns of variation in these brain regions. As the volumes of both these regions also correlated with brain volume (BV) in our models, we tested whether they show the same pattern of evolution in response to changes in BV and found that the do. Therefore, we show that the primary brain nuclei underlying reproductive behaviour in vertebrates can evolve in a mosaic fashion, differently between males and females, likely in response to sexual selection, and that these same regions are simultaneously evolving in concert in relation to overall brain size.
authors.affiliation: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Acton, ACT, Australia.
authors.forename: D
authors.initials: D
authors.lastname: Hoops
authors.affiliation: Center for Advanced Imaging, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: J F P
authors.initials: JF
authors.lastname: Ullmann
authors.affiliation: Center for Advanced Imaging, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: A L
authors.initials: AL
authors.lastname: Janke
authors.affiliation: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Acton, ACT, Australia.
authors.forename: M
authors.initials: M
authors.lastname: Vidal-Garcia
authors.affiliation: Nanoscale Organization and Dynamics Group, School of Science and Health, University of Western Sydney, Penrith, NSW, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Stait-Gardner
authors.affiliation: Nanoscale Organization and Dynamics Group, School of Science and Health, University of Western Sydney, Penrith, NSW, Australia.
authors.forename: Y
authors.initials: Y
authors.lastname: Dwihapsari
authors.affiliation: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Acton, ACT, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Merkling
authors.affiliation: Nanoscale Organization and Dynamics Group, School of Science and Health, University of Western Sydney, Penrith, NSW, Australia.
authors.forename: W S
authors.initials: WS
authors.lastname: Price
authors.affiliation: Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, Waurn Ponds, Vic., Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Endler
authors.affiliation: Department of Biological Sciences, Discipline of Brain, Behavior and Evolution, Macquarie University, Sydney, NSW, Australia.
authors.forename: M J
authors.initials: MJ
authors.lastname: Whiting
authors.affiliation: Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Acton, ACT, Australia.
authors.forename: J S
authors.initials: JS
authors.lastname: Keogh
mesh_terms: D000818:Animals; D001921:Brain / Q000033:anatomy & histology*; D005260:Female; D008116:Lizards / Q000033:anatomy & histology*; D008297:Male; D052586:Mating Preference, Animal; D012727:Sex Characteristics; D012725:Sexual Behavior; D012726:Sexual Behavior, Animal
keywords: agamid; lizard; magnetic resonance imaging; medial preoptic nucleus; neuroscience; reptile; sexual dichromatism; sexual dimorphism; ventromedial hypothalamic nucleus; visual modelling