Evolution of Biomechanical Novelties and the Mechanical Properties of Cranial Ligaments in Wrasses and Parrotfishes (Family: Labridae)

Biomechanical systems such as feeding or locomotor morphologies are usually composed of a complex network of traits and applying the concepts of modularity and integration to these systems may be particularly informative. Fish skulls are a complex skeletal structure composed of up to 30 different bony elements, many of which are connected to other bones through ligaments or muscle via tendons. These soft tissues create essential connections in the skull that allow for force transmission through the skull and concurrently permit the bones to move as a cohesive unit during feeding. Several cranial ligaments have previously been shown to be important for high performance feeding behavior, however the structure and function of connective tissues in fishes has received relatively little attention. In this doctoral dissertation, I aim to understand how the linkage systems created by skeletal elements and connected by ligaments contribute to the diversity of skull shape, to assess the relative importance of various ligament properties to the mobility of the skull, and to explore how ligaments transmit force and control the movement of the skull during feeding using the wrasses (family Labridae). The fish family Labridae is a monophyletic group of over 600 species of coral reef fishes with a large diversity in diet, skull shape, and cranial mobility. By integrating morphometrics, tissue biomechanics, and histology with a well resolved phylogeny this dissertation research advances our understanding of skull diversity in reef fishes through three major aims. First, 3D geometric morphometric data were collected in a 205 species of labrids, and modularity and integration techniques were used to understand how linkages evolve in the wrasse skull. Second, mechanical and structural properties of three cranial ligaments were measured to understand the relative importance of these traits to cranial kinesis and force transmission in the skull. Third, this research program examined the patterns of ligament property evolution across a wide range of feeding behaviors. Overall, this thesis helps to better understand how ligaments and linkages have evolved and function in the skull and allows for better predictions of the influence of ligamentous properties on cranial movement. This research will make significant advances at the level of tissue biomechanics and add to the knowledge of skull mechanics in a complex functional system in one of the major evolutionary radiations of marine fishes.