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Title: Disentangling the Roles of Form and Motion in Fish Swimming Performance
Abstract: A central theme of comparative biomechanics is linking patterns of variation in morphology with variation in locomotor performance. This presents a unique challenge in fishes, given their extraordinary morphological diversity and their complex fluid-structure interactions. This challenge is compounded by the fact that fishes with varying anatomy also use different kinematics, making it difficult to disentangle the effects of morphology and kinematics on performance. My dissertation used interdisciplinary methods to study evolutionary variation in body shape with respect to its consequences for swimming performance.
In Chapter 1, I used bio-inspired mechanical models of caudal fins to study the effects of two evolutionary trends in fish morphology, forked tails and tapered caudal peduncles, on swimming performance. I demonstrated that shape and stiffness interact, making prediction of performance from shape alone questionable; and that correlated variation across body parts may be necessary to reap the benefits of any one body part’s specialized morphology. This suggested that if there were locomotor adaptations in fish morphology, they should occur as correlated suites of morphological change.
In Chapter 2, following the hypothesis that locomotor specialization should occur as correlated morphological changes, I studied body and fin shape evolution in the cichlid fishes. I demonstrated that the body and fins show correlated evolution corresponding to purported ecomorphological specializations. However, morphological evolution suggesting locomotor adaptation is not itself proof of adaptive differences in locomotor performance.
Without being able to account for other traits contributing to swimming performance, it is impossible to ascribe performance differences to morphology alone. In Chapter 3, I developed a method for measuring steady swimming kinematics and performance that allows comparison across species, separating form from kinematics. I used this method to demonstrate the confounding effects of kinematics and morphology in three species of cichlid that are considered ecomorphological specialists. Finally, in Chapter 4, I tested several means of comparing unsteady kinematics and performance across species. Combined, these studies highlight the multivariate nature of morphological evolution, the need to incorporate both morphology and kinematics when determining their effects on performance, and provide a means of disentangling kinematics from morphology for statistical and phylogenetic comparison.