A MODEL SYSTEM OF STRUCTURAL DUPLICATION - HOMOLOGIES OF ADDUCTOR MANDIBULAE MUSCLES IN TETRAODONTIFORM FISHES

We critically reviewed the homologies of the jaw muscles in tetraodont iform fishes (Triacanthoidea, Balistoidea, Tetraodontoidea), as first described in Winterbottom's phylogenetic monograph (1974, Smithson. Co ntrib. Zool. 155:1-201), as a case study in structural duplication. Wi thin this order of teleost fishes, the two main adductor mandibulae mu scles, Al and A2, are duplicated one or more times in some subclades. The number of descendant Al and A2 muscles ranges from as few as the o riginal two muscles in triplespines to as many as eight muscles in som e filefishes. As first pointed out by Winterbottom, the homologies of some muscles are unclear, particularly in comparisons between the supe rfamilies Balistoidea (boxfishes, triggerfishes, filefishes) and Tetra odontoidea (pursefishes, molas, puffers, porcupinefishes). We reassess ed the homologies (orthologs and paralogs) of these Al and A2 muscles based on their origins, insertions, and relative masses in representat ive taxa and their congruence with a phylogeny for these taxa. New nam es that reflect the homologies of these muscles are presented. Ten mus cle duplications by subdivision and three phylogenetic losses of muscl es have occurred in this system. No relationship was found between the number of separate muscles and the relative masses of the Al or A2 mu scles, suggesting that muscle duplication events essentially repackage existing muscle tissue. However, both Al and A2 muscle masses are cor related with each other and with the feeding ecology of these fishes. Durophagous taxa have relatively larger Al and A2 muscles, whereas pla nktivores and benthic grazers have relatively smaller A2 muscles.