Ecological diversification associated with the pharyngeal jaw diversity of Neotropical cichlid fishes

Abstract

Innovations can facilitate bursts of diversification by increasing access to novel resources and the attainment of novel functional designs. Pharyngognathy, exhibited by highly diverse groups such as wrasses and cichlid fishes, is hypothesized to increase foraging capacity and efficiency. Here, I test the hypothesis that pharyngeal jaw shape and tooth morphology are adaptive in an ecologically diverse radiation of Neotropical cichlid fishes that spans North, Central and South America. I partitioned species into generalized trophic guilds using published stomach content analyses and quantified shape variation of the lower pharyngeal jaw (LPJ) using geometric morphometrics. Additionally, I tested for convergence in LPJ shape and trophic guild by mapping the phylogeny onto the principal components and testing for shifts towards similar evolutionary regimes. Major LPJ shape variation included the length and orientation (i.e. narrow or wide) of the lateral processes and length of the medial process, which varied based on the proportion of fishes and plants consumed. Pharyngeal tooth number, diversity and the frequency of tooth types were not evenly distributed among trophic guilds. There were seven distinct evolutionary regimes that converged upon four optima. Pharyngeal jaw diversification is associated with the exploitation of novel resources among Neotropical cichlids such that pharyngeal specialization has increased access to otherwise poorly accessible resources, such as resources that are difficult to crush (e.g. hard-shelled organisms) and assimilate (e.g. algae).

Keywords: Cichlidae; adaptive radiation; co-evolution; dentition; functional morphology; guild; niche; pharyngognathy.