Something to sink your teeth into: the mechanics of tooth indentation in frugivorous fishes

Frugivorous vertebrates engage in a mutualism with fruiting plants: the former receive a nutrient subsidy, and the latter benefit by having their seeds dispersed far from parent plants. Vertebrate frugivores like primates and bats have particular morphologies suited for gripping fruit and then pulverizing fruit soft tissues; however, variation among frugivores and fruits has made the identification of common frugivore phenotypes difficult. Here, we evaluated the performance of frugivorous fish (pacu and piranha; Serrasalmidae) dentitions when puncturing fruits and seeds and compared specialist frugivorous species to facultative frugivorous and non-herbivorous relatives. We also explored how fruit characteristics affect puncture performance and how the indentation of fruit differs mechanically from harder foods like nuts. Based on expectations from studies on frugivorous bats and primates, we expected that frugivore dentitions would exhibit low force and then high work when engaging fruit tissues. Aligning with our expectation, the specialized frugivorous pacu, Colossoma , had dental performance that matched this low force, high work prediction. We also document how frugivory in omnivorous piranhas may be driven more by seed predation than a focus on softer fruit tissues like pulp. Overall, this study demonstrates remarkable similarity in the form and function of frugivore dentitions across vertebrates.