Evolution of reproductive strategies and male sexual ornaments in poeciliid fishes as inferred by mitochondrial 16 rRNA gene phylogeny

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Abstract
Poeciliid fishes have been widely used as a model system in the study of sexual selection mechanisms. In several species belonging to the genera Xiphophorus and Poecilia males show conspicuous ornaments and use courtship display to obtain female cooperation during mating. Conversely most of the remaining poeciliids are drab and achieve copulation mainly through gonopodial thrusting, a fertilization strategy that bypasses the female's consent. We sequenced a portion of the large (16S) mitochondrial ribosomal RNA gene to estimate the phylogenetic relationships among the five tribes of the subfamily Poeciliinae (ROSEN & BAYLEY 1963) and we used the molecular phylogeny to reconstruct the origin of male ornaments and the evolutionary history of the reproductive strategies in this family. Gambusiini were found to be the basal tribe in the subfamily Poeciliinae. In our phylogeny, Xiphophorus and Poecilia were not closely related thus suggesting that the tribe Poeciliini is not a monophyletic group. Gonopodial thrusting was probably the primitive mating strategy of the poeciliids. Sexual ornaments and elaborate courtship behaviour apparently evolved more recently in the genus Xiphophorus and independently in the genus Poecilia.