title: Artificial selection on male genitalia length alters female brain size.
abstract: Male harassment is a classic example of how sexual conflict over mating leads to sex-specific behavioural adaptations. Females often suffer significant costs from males attempting forced copulations, and the sexes can be in an arms race over male coercion. Yet, despite recent recognition that divergent sex-specific interests in reproduction can affect brain evolution, sexual conflict has not been addressed in this context. Here, we investigate whether artificial selection on a correlate of male success at coercion, genital length, affects brain anatomy in males and females. We analysed the brains of eastern mosquitofish (Gambusia holbrooki), which had been artificially selected for long or short gonopodium, thereby mimicking selection arising from differing levels of male harassment. By analogy to how prey species often have relatively larger brains than their predators, we found that female, but not male, brain size was greater following selection for a longer gonopodium. Brain subregion volumes remained unchanged. These results suggest that there is a positive genetic correlation between male gonopodium length and female brain size, which is possibly linked to increased female cognitive ability to avoid male coercion. We propose that sexual conflict is an important factor in the evolution of brain anatomy and cognitive ability.
authors.affiliation: Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, 10691 Stockholm, Sweden severine.buechel@zoologi.su.se.
authors.forename: Séverine D
authors.identifier: 0000-0002-2385-2973
authors.initials: SD
authors.lastname: Buechel
authors.affiliation: Division of Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia.
authors.forename: Isobel
authors.initials: I
authors.lastname: Booksmythe
authors.affiliation: Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, 10691 Stockholm, Sweden.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kotrschal
authors.affiliation: Division of Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Jennions
authors.affiliation: Department of Zoology/Ethology, Stockholm University, Svante Arrhenius väg 18B, 10691 Stockholm, Sweden.
authors.forename: Niclas
authors.initials: N
authors.lastname: Kolm
mesh_terms: D000818:Animals; D001921:Brain / Q000033:anatomy & histology*; D003307:Copulation; D003532:Cyprinodontiformes / Q000033:anatomy & histology*; D005260:Female; D005837:Genitalia, Male / Q000033:anatomy & histology*; D008297:Male; D009929:Organ Size; D012098:Reproduction; D012641:Selection, Genetic; D012726:Sexual Behavior, Animal
keywords: Gambusia holbrooki; brain evolution; gonopodium; male harassment; sexual conflict; sexual dimorphism