Biomechanics of terrestrial locomotion in bats

This dissertation concerns the way in which bats move on the ground. Chapter one is a literature review on the subject, from an evolutionary perspective, that includes contributions from this thesis. In chapter two, I test an hypothesis frequently used to explain the poor crawling abilities of bats compared with mammals that do not fly. According to that hypothesis, most bats shuffle awkwardly because their hindlimbs are too long and slender to support their body weights, but vampire bats walk well because their hindlimbs are more robust than those of other bats. I used force plates to test a prediction of the hindlimb-strength hypothesis that the peak hindlimb forces of walking vampire bats should be greater than the forces exerted by the legs of poorly crawling bats. I found that shuffling bats (Pteronotus parnellii) exert larger hindlimb forces than walking vampire bats do (Desmodus rotundus, Diaemus youngi). Additionally, I used a simple engineering model of bone stress to demonstrate that the hindlimbs of vampire bats fall within the range of shapes seen in bats that do not walk well. These results do not support the hindlimb-strength hypothesis. In chapter three, I describe the running gait of Common Vampire Bats (D. rotundus). At low speeds, these bats use a lateral sequence walking gait, similar to those of other tetrapods, but switch at higher speeds to a bounding gait that is powered by the forelimbs. This gait is unique to vampire bats, and appears to be independently evolved form the running gaits of other tetrapods. In chapter four, I compare the kinematics of locomotion in Common Vampire Bats to those of another terrestrially adept species, New Zealand short-tailed bats (Mystacina tuberculata). The latter use a lateral sequence walk similar to that of D. rotundus and other tetrapods, but do not perform the bounding run. Using force plates to examine the kinetics of their single kinematic gait, I found that the gait of M. tuberculata is a kinetically run-like, and does not shift from a kinetic walk to kinetic run with increased speed the way the gaits of some other animals do

Kinematic Plasticity during Flight in Fruit Bats: Individual Variability in Response to Loading

All bats experience daily and seasonal fluctuation in body mass. An increase in mass requires changes in flight kinematics to produce the extra lift necessary to compensate for increased weight. How bats modify their kinematics to increase lift, however, is not well understood. In this study, we investigated the effect of a 20% increase in mass on flight kinematics for Cynopterus brachyotis, the lesser dog-faced fruit bat. We reconstructed the 3D wing kinematics and how they changed with the additional mass. Bats showed a marked change in wing kinematics in response to loading, but changes varied among individuals. Each bat adjusted a different combination of kinematic parameters to increase lift, indicating that aerodynamic force generation can be modulated in multiple ways. Two main kinematic strategies were distinguished: bats either changed the motion of the wings by primarily increasing wingbeat frequency, or changed the configuration of the wings by increasing wing area and camber. The complex, individual-dependent response to increased loading in our bats points to an underappreciated aspect of locomotor control, in which the inherent complexity of the biomechanical system allows for kinematic plasticity. The kinematic plasticity and functional redundancy observed in bat flight can have evolutionary consequences, such as an increase potential for morphological and kinematic diversification due to weakened locomotor trade-offs

The crouching of the shrew: Mechanical consequences of limb posture in small mammals

An important trend in the early evolution of mammals was the shift from a sprawling stance, whereby the legs are held in a more abducted position, to a parasagittal one, in which the legs extend more downward. After that transition, many mammals shifted from a crouching stance to a more upright one. It is hypothesized that one consequence of these transitions was a decrease in the total mechanical power required for locomotion, because side-to-side accelerations of the body have become smaller, and thus less costly with changes in limb orientation. To test this hypothesis we compared the kinetics of locomotion in two mammals of body size close to those of early mammals (< 40 g), both with parasagittally oriented limbs: a crouching shrew (Blarina brevicauda; 5 animals, 17 trials) and a more upright vole (Microtus pennsylvanicus; 4 animals, 22 trials). As predicted, voles used less mechanical power per unit body mass to perform steady locomotion than shrews did (P = 0.03). However, while lateral forces were indeed smaller in voles (15.6 ± 2.0% body weight) than in shrews (26.4 ± 10.9%; P = 0.046), the power used to move the body from side-to-side was negligible, making up less than 5% of total power in both shrews and voles. The most power consumed for both species was that used to accelerate the body in the direction of travel, and this was much larger for shrews than for voles (P = 0.01). We conclude that side-to-side accelerations are negligible for small mammals–whether crouching or more upright–compared to their sprawling ancestors, and that a more upright posture further decreases the cost of locomotion compared to crouching by helping to maintain the body’s momentum in the direction of travel

Data from: The crouching of the shrew: mechanical consequences of limb posture in small mammals

An important trend in the early evolution of mammals was the shift from a sprawling stance, whereby the legs are held in a more abducted position, to a parasagittal one, in which the legs extend more downward. After that transition, many mammals shifted from a crouching stance to a more upright one. It is hypothesized that one consequence of these transitions was a decrease in the total mechanical power required for locomotion, because side-to-side accelerations of the body have become smaller, and thus less costly with changes in limb orientation. To test this hypothesis we compared the kinetics of locomotion in two mammals of body size close to those of early mammals (< 40 g), both with parasagittally oriented limbs: a crouching shrew (Blarina brevicauda; 5 animals, 17 trials) and a more upright vole (Microtus pennsylvanicus; 4 animals, 22 trials). As predicted, voles used less mechanical power per unit body mass to perform steady locomotion than shrews did (P = 0.03). However, while lateral forces were indeed smaller in voles (15.6 ± 2.0% body weight) than in shrews (26.4 ± 10.9%; P = 0.046), the power used to move the body from side-to-side was negligible, making up less than 5% of total power in both shrews and voles. The most power consumed for both species was that used to accelerate the body in the direction of travel, and this was much larger for shrews than for voles (P = 0.01). We conclude that side-to-side accelerations are negligible for small mammals–whether crouching or more upright–compared to their sprawling ancestors, and that a more upright posture further decreases the cost of locomotion compared to crouching by helping to maintain the body’s momentum in the direction of travel

Using a creativity-based assignment to improve science communication skills and overcome misconceptions

There are many desired outcomes of science undergraduate education, such as knowledge acquisition and development of science process skills. How can we achieve these outcomes in meaningful ways for students? We present here a novel creativity-based assignment and course experience that has the following goals: (1) Improve student science communication skills; (2) Increase student awareness of topical science content (in this case, antibiotic-resistance, ABR); (3) Assist students in self-identifying their own science misconceptions; and (4) Overcome persistent misconceptions. Students enrolled in an Introductory Genetics class at the University of Toronto Mississauga were instructed to consult the peer-reviewed literature, select a public misconception about ABR, and create an animation targeting the public to overcome this misconception. Pre- and post-testing showed resolution of persistent student ABR misconceptions. The outcomes of this session are to: (1) shed light on the role of such activities in the elimination of misconceptions; (2) discuss and share teaching and learning strategies involving creativity-based assignments; (3) discuss and share progress and pitfalls of incorporating creativity-based assignments into large classes; (4) showcase a selection of student creative work; and (5) encourage audience participation in the active learning assessment strategies that were used with this assignment

Force Plate Recordings for the 39 trials in the study

key_to_all_trials.csv gives metadata for each force plate recording (which individual, its mass, initial velocity, etc.). The 39 other files are each recordings from an individual force plate trial, truncated from left hind footfall to left hind footfall (one stride cycle)

Kinematic Plasticity during Flight in Fruit Bats: Individual Variability in Response to Loading

All bats experience daily and seasonal fluctuation in body mass. An increase in mass requires changes in flight kinematics to produce the extra lift necessary to compensate for increased weight. How bats modify their kinematics to increase lift, however, is not well understood. In this study, we investigated the effect of a 20% increase in mass on flight kinematics for Cynopterus brachyotis, the lesser dog-faced fruit bat. We reconstructed the 3D wing kinematics and how they changed with the additional mass. Bats showed a marked change in wing kinematics in response to loading, but changes varied among individuals. Each bat adjusted a different combination of kinematic parameters to increase lift, indicating that aerodynamic force generation can be modulated in multiple ways. Two main kinematic strategies were distinguished: bats either changed the motion of the wings by primarily increasing wingbeat frequency, or changed the configuration of the wings by increasing wing area and camber. The complex, individual-dependent response to increased loading in our bats points to an underappreciated aspect of locomotor control, in which the inherent complexity of the biomechanical system allows for kinematic plasticity. The kinematic plasticity and functional redundancy observed in bat flight can have evolutionary consequences, such as an increase potential for morphological and kinematic diversification due to weakened locomotor trade-offs.</p

EulerAngles

Measured and Simulated Euler angles as a function of time for all 12 trials discussed in the manuscrip