The Evolution of Feeding Mechanics in the Danioninae, or Why Giant Danios Don't Suck Like Zebrafish

Abstract

Synopsis By linking anatomical structure to mechanical performance we can improve our understanding of how selection shapes morphology. Here we examined the functional morphology of feeding in fshes of the subfamily Danioninae (order Cypriniformes) to determine aspects of cranial evolution connected with their trophic diversifcation. The Danioninae comprise three major lineages and each employs a di?erent feeding strategy. We gathered data on skull form and function from species in each clade, then assessed their evolutionary dynamics using phylogenetic-comparative methods. Di?erences between clades are strongly associated with di?erences in jaw protrusion. The paedomorphic Danionella clade does not use jaw protrusion at all, members of the Danio clade use jaw protrusion for suction production and prey capture, and members of the sister clade to Danio (e.g., Devario and Microdevario) use jaw protrusion to retain prey after capture. The shape of the premaxillary bone is a major determinant of protrusion ability, and premaxilla morphology in each of these lineages is consistent with their protrusion strategies. Premaxilla shapes have evolved rapidly, which indicates that they have been subjected to strong selection. We compared premaxilla development in giant danio (Devario aequipinnatus) and zebrafsh (Danio rerio) and discuss a developmental mechanism that could shift danionine fshes between the feeding strategies employed by these species and their respective clades. We also identifed a highly integrated evolutionary module that has been an important factor in the evolution of trophic mechanics within the Danioninae.