Mechanical effects on the development and evolution of locomotor form and function

Organisms such as fish that spend a significant amount of time developing outside the parent's body have to integrate the stimuli that result from their interaction with the environment with the developmental process that will give rise to adult morphology and hence function. One of the main stimuli experienced by swimming fish is the mechanical stimulus of moving water.;Do the physical conditions in which developing fish swim constrain their locomotor function? To study this question I describe the ontogeny of fin function during routine turns in the zebrafish, Danio rerio. An ontogenetic series of zebrafish was filmed while performing routine turns. Images were analyzed using a novel application of image cross-correlation to calculate body and fin velocities. I found a transition in locomotor performance at a body size of approximately 1 cm. This body size does not coincide with the transition from viscous to inertial hydrodynamic regimens but instead coincides with major morphological changes.;Development clearly affects locomotor function but is normal locomotor function required for normal development? Zebrafish larvae were hatched at 2 days post fertilization (dpf) and placed directly in one of four viscosity treatments: 1, 5, 10 or 15 mPa·s until the fish reached 5 or 7 dpf. The performance of routine turns was then described and surprisingly some aspects of turning were the same in all of the larvae despite them not having had the same hydrodynamic experience. Furthermore, any effects of viscosity were specific to turn stages.;To examine the hydrodynamics and motor control of each turn stage, an adult behavior powered by maximum muscle performance was studied under two increased viscosity treatments. Surprisingly fish were still able to perform escape turns that looked remarkably similar to the turns of fish in water, although multivariate statistics were able to differentiate turns from each viscosity.;Lastly I examined whether the ossification of myoseptal tendons in teleosts is a result of phylogeny or of biomechanics. My results indicate that the values of many morphometric variables differ between fish that have a tendon ossified and those that do not after phylogeny has been taken into account.