title: The evolution of sex roles in birds is related to adult sex ratio.
abstract: Sex-role reversal represents a formidable challenge for evolutionary biologists, since it is not clear which ecological, life-history or social factors facilitated conventional sex roles (female care and male-male competition for mates) to be reversed (male care and female-female competition). Classic theories suggested ecological or life-history predictors of role reversal, but most studies failed to support these hypotheses. Recent theory however predicts that sex-role reversal should be driven by male-biased adult sex ratio (ASR). Here we test this prediction for the first time using phylogenetic comparative analyses. Consistent with theory, both mating system and parental care are strongly related to ASR in shorebirds: conventional sex roles are exhibited by species with female-biased ASR, whereas sex-role reversal is associated with male-biased ASR. These results suggest that social environment has a strong influence on breeding systems and therefore revealing the causes of ASR variation in wild populations is essential for understanding sex role evolution.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK. a.liker@sheffield.ac.uk
authors.forename: András
authors.initials: A
authors.lastname: Liker
authors.forename: Robert P
authors.initials: RP
authors.lastname: Freckleton
authors.forename: Tamás
authors.initials: T
authors.lastname: Székely
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D005075:Biological Evolution; D046091:Charadriiformes / Q000502:physiology*; D005260:Female; D008297:Male; D010802:Phylogeny; D012727:Sex Characteristics; D012744:Sex Ratio; D012726:Sexual Behavior, Animal / Q000502:physiology*