No evidence for size-assortative mating in the wild despite mutual mate choice in sex-role-reversed pipefishes

Size-assortative mating is a nonrandom association of body size between members of mating pairs and is expected to be common in species with mutual preferences for body size. In this study, we investigated whether there is direct evidence for size-assortative mating in two species of pipefishes, Syngnathus floridae and S. typhle, that share the characteristics of male pregnancy, sex-role reversal, and a polygynandrous mating system. We take advantage of microsatellite-based “genetic-capture” techniques to match wild-caught females with female genotypes reconstructed from broods of pregnant males and use these data to explore patterns of size-assortative mating in these species. We also develop a simulation model to explore how positive, negative, and antagonistic preferences of each sex for body size affect size-assortative mating. Contrary to expectations, we were unable to find any evidence of size-assortative mating in either species at different geographic locations or at different ...