FERRY-GRAHAM, LA; WAINWRIGHT, PC; NEAR, TJ; UC Davis; UC Davis; UC Davis: Pharyngeal Jaw Form, Function, and Evolution in the Labroidei

The teleost clade Labroidei (labrids, cichlids, pomacentrids + embiotocids) is characterized as having functional and morphological novelties associated with the pharyngeal jaw apparatus (PJA); most notably extension and fusion of muscles to form a sling that supports the fused 5th ceratobranchial, or lower pharyngeal jaw (LPJ). A suite of PJA characters was used to unite the fishes into a monophyletic group. However, recent molecular studies have not supported labroid monophyly. Thus, PJA modifications may be convergent, or perhaps are not as similar as we once thought. Given that much of the success and diversity of the labroid fishes is attributed to the novel PJA, we sought to 1) understand more fully labroid relationships within the teleosts, and to 2) re-examine the anatomy and function of the PJA specifically in labrids and cichlids. Our generation of phylogenetic hypotheses from mitochondrial and nuclear-encoded gene DNA sequences using maximum parsimony and maximum likelihood optimality criteria also did not suggest labroid monophyly. Our examination of PJA anatomy in five distantly-related cichlid species and four similarly diverse labrid species revealed differences in which PJA muscles are hypertrophied; the external levator (LE3/4) in cichlids and the posterior levator (LP) in labrids. Further, examination of the juvenile labrids Semicossyphus pulcher and Bodianus ssp. suggested that the basal condition in labrids, like cichlids, may be a single sling supporting the LPJ. But, as above, the sling is formed by the LE3/4 in cichlids and the LP in labrids. Our investigation of PJA function in S. pulcher and the basal cichlid Paretroplus menarambo indicated that muscle activity patterns, as indicated by electromyography, were remarkably similar suggesting functional convergence between the groups.