Functional morphology and biomechanics
Click on each topic for a more detailed description
Maximal running speed in mammals
The relationship between locomotor performance and body mass in terrestrial mammals does not follow a single linear trend when the entire range of body mass is considered. Large taxa tend to show different scaling exponents compared to those of small taxa, suggesting that there would be a differential scaling between small and large mammals. I obtained estimations of maximum running speed for 142 species of mammals of several orders, spanning a wide range of sizes. The scaling of relative locomotor performance proved to be non-linear when the entire range of body masses was considered and showed a differential scaling between small and large mammals. Among the small species, a negative, although nearly independent, relationship with body mass was noted. In contrast, maximum relative running speed in large mammals showed a strong negative relationship with body mass. This reduction in locomotor performance was correlated with a decrease in the ability to withstand the forces applied on bones and may be understood as a necessary stress reduction mechanism for assuring the structural integrity of the limb skeleton in large species.
Gait transition in rodents
The transition from trot to gallop in quadruped mammals has been widely hypothesized to be a strategy to minimize the energetic costs of running. This view, however, has been challenged by some experimental evidence suggesting instead that this transition might be triggered by mechanical cues, and would occur when musculoskeletal stresses reach a certain critical value. In this study we evaluated the effect of carrying loads on the locomotor energetics and gait transitions of the rodent Octodon degus running on a treadmill. Metabolic rate and cost of transport increased about 30% with a 20% increment in body mass. This increment was higher than expectations based on other mammals, where energy consumption increases in proportion to the added mass, but similar to the response of humans to loads. No abrupt change of energy consumption between gaits was observed and therefore no evidence was found to support the energetic hypothesis. The trot–gallop transition speed did not vary when subjects were experimentally loaded, suggesting that the forces applied to the musculoskeletal system do not trigger gait transition in small mammals.
and flight behavior
Wing morphology and flight behavior
Interconnections between morphological design and function are central to biology, as they underlie naturla patterns in species distributions, phylogenetic diversification, and morphological specialization. The morphological and ecological diversity observed in bats make this group an excellent candidate to study the causal relationships between organismal design and behavioral performance, particularly related to flight abilities.
Most flying organisms turn by rolling their bodies into a bank, thus orienting the lift produced laterally and generating a side or centripetal force. By examining fruit bats performing 90-degree turns in a flight corridor, we found that bats turn not only by banking their bodies but also by orienting the thrust component towards the direction of the turn. This is achieved by rotating the body around the center of mass during the upstroke in such a way that at the beginning of the downstroke, the body is already oriented into the turn. As a consequence, during the downstroke, both lift and thrust are going to contribute to the generation of centripetal force. Such a mechanism is expected to improve turning performance with respect to turns where only lift is used to produce centripetal force.
Effect of inertia on flight kinematics
During slow flight, some flying vertebrates produce a "tip-reversal upstroke", where the distal portion of the wing moves upward and backward with respect to still air. It has long been thought that this upstroke motion generates thrust which is consistent with the forward acceleration of the body observed during upstroke. Measuring 3D kinematics and modelling the mass distribution of the body and wings during flight, we found that most of the forward acceleration observed during upstroke is due to the inertial effect of moving the massive wings backward and that most of the aerodynamic force that accelerates the body forward is produced during the downstroke.
Load-carrying and flight performance
Bats experience daily and seasonal fluctuations in body mass, which in certain situations can be as much as 40-50% of body mass. Such changes in mass require changes in flight kinematics to modulate lift production. How lift generation is modulated in bats,however, is not well understood. By comparing the wingbeat kinematics of bats flying with loads with normal flight kinematics, we can begin to address how bats modulate aerodynamic force generation. Interestingly, we found consistent individual differences in their response to loading, with some subjects changing the motion of the wing (mostly by changing wingbeat frequency) and with other subjects changing the shape of the wing (changing wing area and wing camber). These results indicate that bats present kinematic plasticity in their response to loading, and that different strategies exist to maintain an appropriate flight performance.
Strain and stress patterns
We are currently investigating the stress and strain environment of the mandible during different feeding behaviors. We use both experimental and modelling approaches to explain how the feeding apparatus responds to the mechanical requirements of feeding. We extend previous analysis by using rousettes strain gages in addition to EMG and detailed 3D kinematics while feeding on foods of different material properties. We also use finite element analysis (FEA) methods to model and test hypotheses regarding the functional significance of variation in morphology and behavior.
3D jaw kinematics during feeding
The kinematics of the jaw reflects interactions between centrally generated motor signals and peripheral sensory feedback from the constantly changing oral environment. Chewing is a strongly modulated behavior that responds to differences in material properties among different type of foods and to changes in the external physical properties of the food as the bolus gets processed. I am using detailed high-speed, 3D kinematics of the mandible to understand how organisms modulate their feeding mechanics. In particular, I am interested in evaluating the hierarchical nature of variation in kinematics among species and individuals, taking advantage of our ability to capture complete feeding sequences of different individuals, different species, feeding on different foods, while collecting kinematics and EMG data.