Research Overview
By studying the relationship between the structure of an organism and the biomechanical functions of that structure, the animal’s morphology can be placed into a broader ecological context of performance. Performance provides an estimate of an organism’s ability to accomplish ecologically relevant tasks such as prey consumption or the ability to escape predators. I am particularly interested in how differences in structure translate to changes in performance. My past and current research illustrates two themes that investigate the relationships among structure, function, and performance: 1) the effects of differences in center of mass position (as a result of morphological, kinematic, or postural changes) on locomotor biomechanics and 2) the evolution of novel head and feeding morphologies and the consequences of changes in head morphology on feeding biology (kinematics, morphology, and biomechanics).
Effects of Differences in Center of Mass Position on Locomotor Biomechanics
The natural environment in which animals move is seldom homogeneous. Instead the locomotor system encounters perturbations and changes in surface properties which the animal must successfully accommodate in order to maintain forward progression. Furthermore, locomotor stability is determined in part by morphology, and changes to morphology can modify the type of stability an animal displays (static vs. dynamic).
The biomechanics of slip recovery in frilled dragons
Bipedal locomotion in lizards has been investigated to address questions about the evolution of bipedalism and the performance of bipedal lizards compared to quadrupedal lizards. Frilled dragons are an excellent system to study the response to, and recovery from, a slip perturbation because they are morphologically similar to other lizards yet are capable of both bipedal and quadrupedal locomotion. Despite the fact that animals often encounter unsteady or unpredictable surfaces and must traverse them while maintaining dynamic stability, most previous locomotor studies have focused on steady state non-perturbed locomotion. As a result, the effects of an unexpected perturbation on center of mass dynamics and subsequent recovery kinematics remain relatively poorly understood. The goal of this study was to describe locomotor kinematics during unperturbed bipedal locomotion, slip perturbation, and the ensuing slip recovery in the frilled dragon, a dynamically stable bipedal runner.
Data indicate that, in response to an unexpected slip perturbation, frilled dragons modify their locomotor kinematics to minimize perturbations to the center of mass and maintain dynamic stability. During the stride in which the slip perturbation occurs, the unperturbed leg responds by touching down faster than during unperturbed runs. However, kinematics return to pre-slip values within one recovery stride indicating that recovery from a slip perturbation in frilled dragons occurs relatively fast. Finally, I found that lower limb kinematics were remarkably similar between slip perturbation trials and steady state non-slip trials. However, during stance the hindlimbs display a greater maximum medio-lateral excursion during slip trials compared to traction and recovery trials. This increased medio-lateral excursion results in a perturbation to the center of mass that the frilled dragon must successfully accommodate in order to maintain dynamic stability (Mara and Hsieh, In Prep). These data will allow me to address questions of perturbation recovery and fall avoidance that are critically important to minimizing the risk of injury due to slip related falls in the elderly and workplace.
The Evolution of novel head and feeding morphologies and the consequences of changes in head morphology on feeding biology
During my time at the University of South Florida, I was involved in numerous collaborative projects with current and former lab members including: feeding morphology and suction performance in nurse sharks (Motta et al., 2008), using forensic analyses of bite damage for species identification (Lowry et al., 2009), bite force and performance in the bonnethead shark (Mara et al., 2010), phylogenetic analysis of the hammerhead family (Lim et al., 2010), and feeding and filter anatomy of the whale shark (Motta et al., 2010). My doctoral training at USF dealt with the functional morphology and biomechanics of the hammerhead feeding apparatus and head.
Evolution of the hammerhead cephalofoil
This research focused on the feeding and head morphology of hammerhead sharks (Sphyrnidae). The relationship between form and function can be used to determine the biological role of a given feature. The study of this relationship, functional morphology, has received considerable attention over the last forty years. By interpreting form and function of phylogenetically closely related organisms a better understanding of the selective forces and constraints that govern their diversity can be obtained. One form of constraint is constructional constraint, whereby spatial limitations are placed on a structure, such as the hammerhead cehalofoil, as a result of multiple biological roles (e.g. respiration, feeding, sensory reception). This is particularly important when considering the size and position of sensory and feeding organs.
The dorsoventrally compressed and laterally expanded pre-branchial cephalofoil of hammerhead sharks offers a unique opportunity to study adaptation in an historical context. By interpreting form and function of a closely related group of organisms, such as hammerhead sharks, in a historical context we can gain a better understanding of the selective forces and constraints that govern the diversity of cranial design. The shape of the cephalofoil ranges from extremely wide (E. blochii – 40-50% of Total Length [TL]) to only moderately expanded (S. tiburo – 18-25% of TL), with concomitant changes in the chondrocranium, jaws, cranial musculature, and neural and sensory apparati. Genetic evidence indicates that the sphyrnid with the most laterally expanded cephalofoil is the most basal, with cephalofoil size decreasing through phylogeny. Various hypotheses have been posited to explain the adaptive significance of the peculiar hammerhead shark head morphology including: increased hydrodynamic lift, prey manipulation, enhanced binocular vision, greater olfactory gradient resolution, and enhanced electroreceptive area.
The goal of this study was to investigate the evolution and function of the hammerhead cephalofoil and the consequences of changes in head shape and form on feeding morphology and sensory structures and to elucidate any potential constructional constraints between or among feeding and sensory structures. The goals for each of my chapters were: Chapter 1: 1) investigate the shape changes of the sphyrnid head through phylogeny; 2) examine the volumetric changes of cephalic elements through phylogeny; and 3) investigate potential constructional constraints between and among feeding, neural and sensory structures. Chapter 2: 1) describe and compare the functional morphology and biomechanics of the feeding apparatus of the hammerhead sharks; 2) investigate if changes to the feeding bauplan exist in sphyrnid shark or if changes are confined to surrounding structures with conservation of the feeding apparatus; and 3) investigate the relationship between cranial design and feeding morphology within this clade. Chapter 3: 1) characterize the mechanical function of the feeding mechanism of S. tiburo through biomechanical modeling of biting and bite force measurements obtained via tetanic stimulation of jaw muscles and restraint of live animals; 2) compare the bite force of S. tiburo with that of other fishes; and 3) identify functional constraints on prey capture and diet by comparing the bite force of S. tiburo to the fracture properties of its primary prey item, blue crabs Callinectes sapidus.
Dissertation AbstractThe relationship between form and function is often used to elucidate the biological role of a structure. Hammerhead sharks offer a unique opportunity to study form and function through phylogeny. Because sphyrnid sharks display a range of cranial morphologies this group can be used to address questions about the evolution of cranial design and investigate the effects of changes in head morphology on feeding structures and bite force. Geometric morphometrics, volumetric analyses, morphological dissections, and phylogenetic analyses of the cephalofoil were used to gain insight into changes in cranial design through evolutionary history. External morphometrics and internal volumetric analyses indicated that while the external shape of the cephalofoil and placement of the sensory structures is variable through evolutionary history, the volumes of the internal cranial elements do not change. Constructional constraints within the cephalofoil were confined to sensory structures while feeding morphology remained relatively unchanged. Analysis of the morphology and biomechanics of the feeding apparatus revealed that through phylogeny the feeding system does not change among sphyrnid species. However, size-removed bite force was lower than predicted for all sphyrnid species except Sphyrna mokarran. Despite differences in head morphology between sphyrnid and carcharhinid sharks, the feeding bauplan is conserved in sphyrnid sharks with few changes to the feeding structures. Instead the chondrocranial and sensory structures are modified around the relatively static feeding core. Finally, the durophagous S. tiburo was found to consume hard prey in a manner that is biomechanically and morphologically different from other durophagous fishes. Furthermore, the diet of S. tiburo is constrained by the properties of its preferred prey.
By studying the relationship between the structure of an organism and the biomechanical functions of that structure, the animal’s morphology can be placed into a broader ecological context of performance. Performance provides an estimate of an organism’s ability to accomplish ecologically relevant tasks such as prey consumption or the ability to escape predators. I am particularly interested in how differences in structure translate to changes in performance. My past and current research illustrates two themes that investigate the relationships among structure, function, and performance: 1) the effects of differences in center of mass position (as a result of morphological, kinematic, or postural changes) on locomotor biomechanics and 2) the evolution of novel head and feeding morphologies and the consequences of changes in head morphology on feeding biology (kinematics, morphology, and biomechanics).
Effects of Differences in Center of Mass Position on Locomotor Biomechanics
The natural environment in which animals move is seldom homogeneous. Instead the locomotor system encounters perturbations and changes in surface properties which the animal must successfully accommodate in order to maintain forward progression. Furthermore, locomotor stability is determined in part by morphology, and changes to morphology can modify the type of stability an animal displays (static vs. dynamic).
The biomechanics of slip recovery in frilled dragons
Bipedal locomotion in lizards has been investigated to address questions about the evolution of bipedalism and the performance of bipedal lizards compared to quadrupedal lizards. Frilled dragons are an excellent system to study the response to, and recovery from, a slip perturbation because they are morphologically similar to other lizards yet are capable of both bipedal and quadrupedal locomotion. Despite the fact that animals often encounter unsteady or unpredictable surfaces and must traverse them while maintaining dynamic stability, most previous locomotor studies have focused on steady state non-perturbed locomotion. As a result, the effects of an unexpected perturbation on center of mass dynamics and subsequent recovery kinematics remain relatively poorly understood. The goal of this study was to describe locomotor kinematics during unperturbed bipedal locomotion, slip perturbation, and the ensuing slip recovery in the frilled dragon, a dynamically stable bipedal runner.
Data indicate that, in response to an unexpected slip perturbation, frilled dragons modify their locomotor kinematics to minimize perturbations to the center of mass and maintain dynamic stability. During the stride in which the slip perturbation occurs, the unperturbed leg responds by touching down faster than during unperturbed runs. However, kinematics return to pre-slip values within one recovery stride indicating that recovery from a slip perturbation in frilled dragons occurs relatively fast. Finally, I found that lower limb kinematics were remarkably similar between slip perturbation trials and steady state non-slip trials. However, during stance the hindlimbs display a greater maximum medio-lateral excursion during slip trials compared to traction and recovery trials. This increased medio-lateral excursion results in a perturbation to the center of mass that the frilled dragon must successfully accommodate in order to maintain dynamic stability (Mara and Hsieh, In Prep). These data will allow me to address questions of perturbation recovery and fall avoidance that are critically important to minimizing the risk of injury due to slip related falls in the elderly and workplace.
The Evolution of novel head and feeding morphologies and the consequences of changes in head morphology on feeding biology
During my time at the University of South Florida, I was involved in numerous collaborative projects with current and former lab members including: feeding morphology and suction performance in nurse sharks (Motta et al., 2008), using forensic analyses of bite damage for species identification (Lowry et al., 2009), bite force and performance in the bonnethead shark (Mara et al., 2010), phylogenetic analysis of the hammerhead family (Lim et al., 2010), and feeding and filter anatomy of the whale shark (Motta et al., 2010). My doctoral training at USF dealt with the functional morphology and biomechanics of the hammerhead feeding apparatus and head.
Evolution of the hammerhead cephalofoil
This research focused on the feeding and head morphology of hammerhead sharks (Sphyrnidae). The relationship between form and function can be used to determine the biological role of a given feature. The study of this relationship, functional morphology, has received considerable attention over the last forty years. By interpreting form and function of phylogenetically closely related organisms a better understanding of the selective forces and constraints that govern their diversity can be obtained. One form of constraint is constructional constraint, whereby spatial limitations are placed on a structure, such as the hammerhead cehalofoil, as a result of multiple biological roles (e.g. respiration, feeding, sensory reception). This is particularly important when considering the size and position of sensory and feeding organs.
The dorsoventrally compressed and laterally expanded pre-branchial cephalofoil of hammerhead sharks offers a unique opportunity to study adaptation in an historical context. By interpreting form and function of a closely related group of organisms, such as hammerhead sharks, in a historical context we can gain a better understanding of the selective forces and constraints that govern the diversity of cranial design. The shape of the cephalofoil ranges from extremely wide (E. blochii – 40-50% of Total Length [TL]) to only moderately expanded (S. tiburo – 18-25% of TL), with concomitant changes in the chondrocranium, jaws, cranial musculature, and neural and sensory apparati. Genetic evidence indicates that the sphyrnid with the most laterally expanded cephalofoil is the most basal, with cephalofoil size decreasing through phylogeny. Various hypotheses have been posited to explain the adaptive significance of the peculiar hammerhead shark head morphology including: increased hydrodynamic lift, prey manipulation, enhanced binocular vision, greater olfactory gradient resolution, and enhanced electroreceptive area.
The goal of this study was to investigate the evolution and function of the hammerhead cephalofoil and the consequences of changes in head shape and form on feeding morphology and sensory structures and to elucidate any potential constructional constraints between or among feeding and sensory structures. The goals for each of my chapters were: Chapter 1: 1) investigate the shape changes of the sphyrnid head through phylogeny; 2) examine the volumetric changes of cephalic elements through phylogeny; and 3) investigate potential constructional constraints between and among feeding, neural and sensory structures. Chapter 2: 1) describe and compare the functional morphology and biomechanics of the feeding apparatus of the hammerhead sharks; 2) investigate if changes to the feeding bauplan exist in sphyrnid shark or if changes are confined to surrounding structures with conservation of the feeding apparatus; and 3) investigate the relationship between cranial design and feeding morphology within this clade. Chapter 3: 1) characterize the mechanical function of the feeding mechanism of S. tiburo through biomechanical modeling of biting and bite force measurements obtained via tetanic stimulation of jaw muscles and restraint of live animals; 2) compare the bite force of S. tiburo with that of other fishes; and 3) identify functional constraints on prey capture and diet by comparing the bite force of S. tiburo to the fracture properties of its primary prey item, blue crabs Callinectes sapidus.
Dissertation AbstractThe relationship between form and function is often used to elucidate the biological role of a structure. Hammerhead sharks offer a unique opportunity to study form and function through phylogeny. Because sphyrnid sharks display a range of cranial morphologies this group can be used to address questions about the evolution of cranial design and investigate the effects of changes in head morphology on feeding structures and bite force. Geometric morphometrics, volumetric analyses, morphological dissections, and phylogenetic analyses of the cephalofoil were used to gain insight into changes in cranial design through evolutionary history. External morphometrics and internal volumetric analyses indicated that while the external shape of the cephalofoil and placement of the sensory structures is variable through evolutionary history, the volumes of the internal cranial elements do not change. Constructional constraints within the cephalofoil were confined to sensory structures while feeding morphology remained relatively unchanged. Analysis of the morphology and biomechanics of the feeding apparatus revealed that through phylogeny the feeding system does not change among sphyrnid species. However, size-removed bite force was lower than predicted for all sphyrnid species except Sphyrna mokarran. Despite differences in head morphology between sphyrnid and carcharhinid sharks, the feeding bauplan is conserved in sphyrnid sharks with few changes to the feeding structures. Instead the chondrocranial and sensory structures are modified around the relatively static feeding core. Finally, the durophagous S. tiburo was found to consume hard prey in a manner that is biomechanically and morphologically different from other durophagous fishes. Furthermore, the diet of S. tiburo is constrained by the properties of its preferred prey.