title: Recurrent origin of a sexually selected trait in Xiphophorus fishes inferred from a molecular phylogeny.
abstract: Darwin believed that sexual selection accounts for the evolution of exaggerated male ornaments, such as the sword-like caudal fin extensions of male fishes of the genus Xiphophorus, that appear detrimental to survival. Swordtails continue to feature prominently in empirical work and theories of sexual selection; the pre-existing bias hypothesis has been offered as an explanation for the evolution of swords in these fishes. Based upon a largely morphological phylogeny, this hypothesis suggests that female preference to mate with sworded males arose in ancestrally swordless species, thus pre-dating the origin of the sword itself and directly driving its evolution. Here we present a molecular phylogeny (based on mitochondrial and nuclear DNA sequences) of Xiphophorus which differs from the traditional one: it indicates that the sword originated and was lost repeatedly. Our phylogeny suggests that the ancestor of the genus is more likely to have possessed a sword than not, thus questioning the applicability of the pre-existing bias hypothesis as an explanation for the evolution of this sexually selected trait.
authors.affiliation: Department of Ecology and Evolution, State University of New York, Stony Brook 11794-5245.
authors.forename: A
authors.initials: A
authors.lastname: Meyer
authors.forename: J M
authors.initials: JM
authors.lastname: Morrissey
authors.forename: M
authors.initials: M
authors.lastname: Schartl
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003532:Cyprinodontiformes / Q000145:classification / Q000235:genetics / Q000502:physiology*; D003573:Cytochrome b Group / Q000235:genetics; D004247:DNA / Q000235:genetics; D017931:DNA Primers; D005260:Female; D008297:Male; D008969:Molecular Sequence Data; D010802:Phylogeny; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D012641:Selection, Genetic; D012677:Sensation; D012727:Sex Characteristics
chemical_list: D003573:Cytochrome b Group; D017931:DNA Primers; D004247:DNA; D011505:Protein-Tyrosine Kinases