Species variation in the degree of sex differences in brain and behaviour related to birdsong: adaptations and constraints

Abstract

One contribution of 16 to a theme issue 'Multifaceted origins of sex differences in the brain'.Subject Areas: behaviour, evolution, neuroscience Keywords: sexual selection, song-control system, HVC, canary Author for correspondence: Gregory F. Ball e-mail: gball@umd.edu Species variation in the degree of sex differences in brain and behaviour related to birdsong: adaptations and constraints The song-control system, a neural circuit that controls the learning and production of birdsong, provided the first example in vertebrates of prominent macro-morphological sex differences in the brain. Forebrain nuclei HVC, robust nucleus of the arcopallium (RA) and area X all exhibit prominent male-biased sex differences in volume in zebra finches and canaries. Subsequent studies compared species that exhibited different degrees of a sex difference in song behaviour and revealed an overall positive correlation between male biases in song behaviour and male biases in the volume of the song nuclei. However, several exceptions have been described in which male biases in HVC and RA are observed even though song behaviour is equal or even female-biased. Other phenotypic measures exhibit lability in both sexes. In the duetting plain-tailed wren (Pheugopedius euophrys), males and females have auditory cells in the song system that are tuned to the joint song the two sexes produce rather than just male or female components. These findings suggest that there may be constraints on the adaptive response of the song system to ecological conditions as assessed by nucleus volume but that other critical variables regulating song can respond so that each sex can modify its song behaviour as needed.

Multifaceted origins of sex differences in the brain

“…In this issue, Ball [51] discusses the potential power of studies on birds owing to the enormous natural variation across the approximately 6000 existing song bird species that live in different climates and habitats and are thus subject to divergent selection. Early studies confirmed a correlative relationship between the degree of sexual dimorphism in the size of song control nuclei and sex differences in song production.…”

Sex Differences in Forebrain Monoaminergic Response to Song Performance

“…The best known differences are sexual dimorphisms in the size and composition of the song-control nuclei, which regulate song learning and production and are typically larger in males [Nottebohm and Arnold, 1976;Arnold, 1992;Ball and MacdougallShackleton, 2001;Ball, 2016]. However, researchers have also detected effects of sex on gene expression and protein levels in the songbird auditory system as well as on auditory perception [Phillmore et al, 2003;Ikebuchi et al, 2003;Pinaud et al, 2006;Krentzel and Remage-Healey, 2015].…”

Sex differences in learning — shared principles across taxa

“…The song nucleus was the first anatomical sexual dimorphism in the vertebrate brain to be linked to a sexually dimorphic learned motor behaviour [28]. The song nucleus is considerably larger in males of species in which only males sing; in duetting species the dimorphism is not as pronounced (for a recent review, see [29]). The anatomical sexual dimorphism of the song nuclei is paralleled by sex differences in expression of the CNTNAP2 gene during development and in the adult [30].…”