The foot is a crucial component to locomotion and is greatly affected by the evolution of new functions. This dissertation examines both functional and morphological aspects of how the evolution of the dry adhesive system is associated with the evolution gecko feet.

In Chapter 1, I obtained obtained 3D movements (with high-speed video) of geckos (Phelsuma madagascariensis) running on a range of ecologically relevant inclines to examine in detail, how geckos modulate their feet with the dry adhesive system. We focused on measuring instantaneous within-foot symmetry and foot alignment relative to the body. On smaller perch diameters, geckos inverted their foot alignment and the hind foot had greater individual digit modulation than the forefoot.

Chapter 2 used a comparative phylogenetic framework to examine how digit morphology and within-foot symmetry changed with the evolution of the adhesive system. I applied geometric morphometric methods to X-rays obtained of both padbearing and padless geckos. Our results confirm that padbearing lineages tend to have shorter digits, greater within-foot symmetry and larger interdigital angles than padless lineages and this suggests repeated shifts to a similar pad-bearing morphology.

In Chapter 3, I obtained microCT scans of padbearing and padless lineages to examine how the evolution of the adhesive system is associated with shape change in the bones (astragalocalcaneum and the fourth distal tarsal) involved in the mesotarsal joint. Our results show that padbearing lineages likely have greater degrees of freedom at the mesotarsal joint as a result of having broader surfaces on the astragalocalcaneum and fourth distal tarsal.

Locomotion is an integral component of the majority of behaviors that dictate the survival of vertebrates. However, the environments through which animals move are often heterogeneous. The arboreal habitat may be one of the most challenging environments due to its wide variation in substrate incline, diameter, compliance, and texture. This array of structural challenges places extreme and varied demands on the locomotor system that muscles, as the units that power this system, must be able to cope with. Although we have a good understanding of the kinematic and neuromuscular modifications employed by animals encountering different inclines, we know virtually nothing about how other structural challenges affect locomotor behavior and in vivo muscle function. In this dissertation, I used a combination of high-speed video, electromyography, in situ contractile experiments, and morphology to understand how arboreal Anolis lizards modulate their behavior and power cyclical locomotion on surfaces of varying incline and perch diameter. Several significant results emerged. First, the forelimb and hind limb were modulated differently in response to changes in substrate; the forelimb likely adopts a greater propulsive role and the hind limb a more stabilizing role on steeper inclines and narrower surfaces. Second, there was a decoupling of the response of limb movements and motor patterns to changes in substrate; perch diameter had a stronger effect on kinematics than incline, whereas muscle activity was more strongly affected by incline than by perch diameter. Third, not only does muscle recruitment, operating length, and capacity for force production change with perch diameter to allow the gastrocnemius, a primary ankle extensor, to contribute more to propulsion on broader than on narrower surfaces, but incline appears to alter the relationship between muscle recruitment and efficiency of force production. Finally, hind limb tendons do not appear to have the potential to stretch and store significant elastic energy during cyclical locomotion in Anolis lizards. Together these data force us to acknowledge the complex nature of mechanisms that power locomotion in the natural world. The environment can clearly have a profound impact on both the coordinated function of limbs and the neural control and physiology of the muscles that power locomotor behaviors.

Locomotion is a central tenet of life for many organisms that is inherently tied to the surrounding physical environment. Geckos represent a speciose and phenotypically diverse clade of lizards that are found within many habitats and move on a variety of substrates. Although much is now known about the integration and mechanics of the highly adept frictional adhesive toe pads from intensive laboratory study within model species, the functional and evolutionary significance of phenotypic diversity within geckos is ripe for investigation. This dissertation thus brings ecological context to the foreground to begin to address this large gap. In Chapter 1, we collected field observations and locomotor trials of surface compliance transitions in a cursorial day gecko, Rhoptropus afer, to examine how this species responds to sudden changes in substrate conditions encountered in nature. This species maintained high-speed running while altering its posture and stance time when transitioning into and out of sand collected from its habitat. In Chapter 2, we used experimental claw manipulation (i.e., partial removal) in the arboreal species, Thecadactylus rapicauda, to assess the functional interplay of adhesive toe pads and claws on natural and artificial surfaces of different roughness. After partial claw removal, static clinging performance significantly declined on non-smooth surfaces, and geckos tended to adjust their foot kinematics to increase contact duration on smooth and rough surfaces at both horizontal and low incline, although their ability to accelerate from a stationary position was not significantly altered. Finally, in Chapter 3, we took a phylogenetic comparative approach (112 gecko species) to test if morphological variation in toe pads and claws represents adaptive evolution to general habitat use. We found that species using more scansorial habitats tended to have larger, longer pads and more curved claws, with saxicolous species having longer setae than all other groups.

In order to understand the evolution of locomotion, lizards are often used to study the relationships between morphology and locomotor performance. However, the mechanisms by which himblimb morphology results in jumping performance are not well understood, despite the fact that jumping may be important for fitness in many lizard species.

Here I investigate the ways in which mechanical power is generated by the hindlimbs of jumping collared lizards, Crotaphytus collaris. I examine the contribution of each hindlimb joint to total power output. I also test the hypothesis that these lizards utilize elastic power amplification.

I found a high degree of individual variation in the relationships between joint kinematics and jump power, suggesting multiple strategies for controlling jump performance and highlighting the importance for considering individual variation in biomechanical studies. I also found peak power outputs exceeding the physiological limits of lizard muscle suggesting the presence of a power amplification mechanism. Additionally, the use of countermovements may enhance jump power, though possibly through mechanisms other than elastic energy storage.

Organismal complexity is often reduced to individual systems, but organisms function as an integrated whole and reductionist studies cannot address the constraints imposed by systems working together to perform a function. In this dissertation, I use integration between locomotor and feeding performance during prey capture in fishes as a model system for understanding complex behaviors and their ecological relevance. First, I demonstrate the empirical utility of integration for describing emergent differences between species. I utilize two species of Pacific marine sculpins capturing live amphipod prey, and confirmed that species were similar in feeding behaviors but different in their use of locomotion during prey capture. This resulted in differences in integration that reflect ecological divergence that would not be apparent in feeding behaviors alone. Second, I demonstrate that differential capture success is due to differences in predator accuracy. I utilize centrarchid sunfishes to develop a non-invasive model of suction volume and accuracy and apply this model to 3D feeding kinematics of three predators capturing two prey types. Not only did accuracy vary across species, but so did the ability to modulate the shape of the ingested volume of water, leading to a direct effect on predator capture success. Finally, I expand the techniques for quantifying behavioral integration to multivariate space and assess the causes and consequences of integration using a single centrarchid predator capturing two prey types. Partial least squares correlations describe multivariate integration and demonstrate that predators rely on performance variables differentially for each prey type. These differences are then reflected in patterns of integration and predator accuracy across prey types. This dissertation advances our understanding of how organismal integration and complexity act to drive performance and ecology. I demonstrate that performance integration is real and can be quantified and establish the empirical and ecological relevance of performance integration. Integration and organismal complexity may be one of the next scientific frontiers, and this dissertation provides a first step in exploring this new direction.

The origin and evolution of pectoral fins remains one of the most important components of vertebrate history. Sharks represent one of the oldest representatives to exhibit paired fins. Yet, there is a paucity of data on the functional and evolutionary aspects of shark pectoral fins. This dissertation aims to bridge those gaps. In Chapter 1, we measured the external pectoral fin morphology of a shark species, the scalloped hammerhead (Sphyrna lewini), that undergoes ecological shifts through ontogeny. We found the pectoral fins changed in shape that are most likely in response the difference in ecological demands that this shark experiences. In Chapter 2, we measured the pectoral fin aspect ratio (AR) of nearly every known (89%) extant shark species and various extinct species. In addition, we coded each species based on their ecology and performed sophisticated evolutionary model fitting analyses. We determined sharks were most likely benthic (i.e., bottom-dwelling) or benthopelagic (i.e., near bottom) in origin and that when sharks shifted to the pelagic (open water) zone of the marine ecosystem, their pectoral fin morphology also changed, clearly demonstrating adaptive evolution. We also realized temperature was a critical driver in shark evolution. In Chapter 3, we used the computational fluid dynamics (CFD) approach to understand the functional aspects of pelagic shark pectoral fins. Our results showed that pelagic shark pectoral fins have different functions compared to benthic sharks. In Chapter 4, we followed up our work in Chapter 1, and compared the scaling trends of shark pectoral fins with various ecologies to determine if any noticeable patterns were present. We realized the scaling of shark pectoral fins is highly complex and that further broader research is warranted.

Physical performance inextricably ties variation in physiology, morphology, and behavior to fitness. By studying how morphology is linked to performance, and the consequences of performance ability on survival and reproduction, evolutionary biologists can understand the selection pressures driving the evolution of particular morphological characteristics. However, many studies of performance are conducted in the lab in order to control external factors, allowing for detailed analyses of a few potentially influential variables but reducing the overall ecological realism of the results. The capacity for field studies to capture natural levels of variability helps to elucidate important ecological factors that influence locomotor performance and therefore drive individual fitness. This dissertation explores the evolution of bipedalism in rodents and the factors that affect their jump performance using a field-based approach. To do this, I investigated (1) the natural jump performance of kangaroo rats (Dipodomys) by filming their escapes from rattlesnake strikes, (2) the conditions under which they utilize these impressive jump escapes, (3) the relationship between hindlimb morphology and jump performance, and (4) how jump performance compares between bipedal and quadrupedal rodents. From these studies, I was able to determine their natural levels of performance, the ecological contexts that place selective pressure on jump performance, how those pressures on performance have shaped the evolution of their hindlimb morphology, and whether bipedality indeed confers improved jump performance when compared to quadrupedal rodents.