Correction to: Metabolic growth hypothesis for the evolution of the nuchal hump in swordtail fishes

Understanding developmental constraints on the evolution of adaptive traits can provide valuable insights into the evolution of phenotypic diversity. In Xiphophorus fishes, a nuchal hump has been described for larger adult males in the species known as the “sheepshead swordtail,” Xiphophorus birchmanni . Here, we describe for the first time the formation of nuchal humps on X. multilineatus males maintained in the laboratory. Factors that influenced the size of the nuchal hump included diet and genotype, with genotypes known to have faster juvenile growth rates forming larger humps. Histological sections stained for lipid droplets, suggesting that the nuchal hump is storing fat. In addition, the size of the hump was positively related to activity level in cold water. Finally, mate preference for this trait was demonstrated in wild-caught X. multilineatus females, suggesting the nuchal hump could be a target of sexual selection if it developed in males in the wild. We consider the results from this study in relation to the diversity in development of the trait across species and introduce a nuchal hump metabolic growth hypothesis to help explain its function in swordtails.