Evidence for positive Darwinian selection on the hepcidin gene of Perciform and Pleuronectiform fishes

Hepcidin is a small cysteine-rich peptide that plays an important role in antimicrobial activity and in maintaining iron homeostasis in vertebrates. Here we report on the underlying mechanism that maintains high sequence diversities among the hepcidin-like variants of perciform and pleuronectiform fishes. In contrast to mammals, maximum likelihood-based codon substitution analyses revealed that positive Darwinian selection (nonsynonymous to synonymous substitution, omega > 1) is the likely cause of accelerated rate of amino acid substitutions in the hepcidin mature peptide region of these fishes. Comparison of models incorporating positive selection (omega > 1) at certain sites with models not incorporating positive selection (omega < 1) failed to reject (p = 0) the evidence of positive selection among the codon sites of percifom and pleuronectiform hepcidin. The adaptive evolution of this peptide in perciform and pleuronectiform fishes might be directed by pathogens when the host is exposed to new habitats/environments.