Functional morphology and developmental biology of zebrafish: reciprocal illumination from an unlikely couple

Functional morphology has benefited greatly from the input oftechniques and thinking from other disciplines. This has beenespecially productive in situations where each discipline hasmade significant contributions to a particular research topic.A combination of methodologies from functional morphology anddevelopmental biology has allowed us to characterize feedingmechanics of first-feeding larval zebrafish (Danio rerio). Contraryto kinematic patterns commonly seen in adult teleosts, larvalzebrafish showed no lateral abduction during the expansive phaseof a suction-feeding event. Instead, dorsoventral expansionof the buccal chamber, more typical of patterns seen in primitivefishes, characterized the expansive phase. Moreover, a pronouncedpreparatory phase during which the buccal chamber is constrictedby the protractor hyoideus was consistently seen in first-feedinglarval kinematics. Key kinematic variables associated with firstfeeding correlated significantly with the hydrodynamic regimeas measured by the Reynolds number. Using the tools of bothfunctional morphology and developmental biology we have notonly determined which cranial muscles are important for successfulfeeding but also uncovered important physiological differencesin muscle structure. Muscles necessary for the rapid dorsoventralexpansion of the head are composed primarily of fast-twitchfibers while those involved in more tonic contractions suchas hyoid protraction have more slow-twitch muscle fibers. Whilemost evolutionary developmental studies have examined mechanismsresponsible for large evolutionary changes in morphology, wepropose that the type of data uncovered in functional studiescan lead to the generation of hypotheses concerning the developmentalmechanisms responsible for smaller intra- and/or interspecificchanges.