Student Opportunities in the Locomotion Lab
Many of my projects involve mentoring undergraduate students with an interest in research. Students are involved with all stages of a project, from project development and construction of equipment to data collection and analysis to manuscript development and publication. Many students who work in my lab have the opportunity to present their work at conferences and/or co-author peer-reviewed publications. |
Previous WorkTetrapod Functional Morphology and Secondary Aquatic Invasions
The invasion of land by early tetrapods is arguably one of the most profound events in vertebrate history. However, equally profound but less often studied is the return of terrestrial vertebrates to highly or exclusively aquatic lifestyles. This secondary shift back to the water is often accompanied by characteristic morphological changes, including the flattening of the shaft of the long bones in the limb. Such morphological changes have largely been attributed to intuitive changes in loading regime between land and water, with reduced body support demands in aquatic habitats. These projects investigated potential mechanisms for how flattening of the limb long bones may come about. Femoral Loading: Strain data from the femur of semi-aquatic Trachemys scripta (slider turtle; Family: Emydidae) confirm the expected reduction in load magnitudes during swimming compared to terrestrial walking. In addition, torsional (twisting) loads on the femur were also significantly reduced during swimming compared to walking. In an environment in which torsional loads are not prevalent (e.g. aquatic), animals may be released from the need to maintain a round cross-sectional shape, thus permitting the shift to a more hydrodynamically advantageous flattened shape of the long bones. Humeral Loading: Data from the humerus of the semi-aquatic Pseudemys concinna (river cooter turtle; Family: Emydidae) show similar patterns to those observed in the slider femur. These data indicate that changes in terrestrial and aquatic loading regime are associated more with a reduction in overall strain magnitude rather than changes in load orientation (change in torsional loads). Thus, despite similar reductions in shear strain between terrestrial and aquatic locomotion, these reductions are produced by different mechanisms. Swimming Kinematics: Specialized performance in a particular habitat often comes at the cost of high performance in contrasting habitats. However, retention of ancestral performance ability in specialist species has been largely unexplored. Despite aquatic ancestry, some turtle lineages have transitioned to exclusively terrestrial habits. Comparison of swimming kinematics of the forelimb and hindlimb of terrestrial tortoises (Testudo horsfieldii) and box turtles (Terrepene carolina) to two semi-aquatic emydid turtles (Trachemys scripta and Chrysemys picta) indicates functional convergence of the forelimb in box turtles and tortoises, but the box turtle hindlimb retains ancestral swimming motions. Phylogenetic Limb-Bone Scaling: Although strain data from turtle humeri and femora indicate a potential mechanism for how flattened limb bone shapes may be achieved, such a mechanism is difficult to assess without considering bone morphology across the functional spectrum exhibited in turtles (including terrestrial walkers, aquatic rowers, and marine flappers/underwater flight). Data were collected from skeletal specimens housed at the American Museum of Natural History, the Carnegie Museum of Natural History, the Florida Museum of Natural History, the Smithsonian National Museum of Natural History, and the Chelonian Research Institute. Limb bone size and shape patterns reflect functional and life history differences among the taxa examined, indicating that limb bone shape is likely governed by a combination of mechanical, ecological, and evolutionary factors. |
Physiological and Morphological Variation in a Stream Salamander
Habitats vary in their biotic and abiotic components across space and time. Such variability can introduce challenges for organisms unless they have the ability to alter physiology and morphology in a way what maximizes fitness. Thermal Acclimation: Theory predicts that highly variable thermal environments should lead to reduced thermal sensitivity in ectotherms, resulting in greater acclimation capacity. Salamanders of the species Desmognathus brimleyorum (Ouachita dusky salamander; Family: Plethodontidae) were exposed to constant and variable thermal conditions in the lab. Following the acclimation period, thermal sensitivity of metabolic rate and swimming performance was assessed across a range of temperatures. Swimming performance did not show a significant difference between treatments (see figure at left showing individual performance curves in black and mean performance in red), however a limited degree of acclimation of metabolic rate was observed. Morphological Variation: Individual salamanders responded to treatments differently depending on which source population they originated from. Furthermore, tail morphology appeared to differ between populations, though sample sizes were too small to statistically confirm this difference. Additional work with this system is necessary to further evaluate the extent of morphological diversity between populations and to determine what environmental elements may be driving these differences in tail shape. |