Research

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Terrestrial locomotion

running dogs Maximal running speed in mammals
Maximum 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.

  • Iriarte-Diaz J (2002) Differential scaling of locomotor performance in small and large terrestrial mammals. J. Exp. Biol. 205: 2897-2908
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    degu Gait transition in rodents
    Gait transition in rodents

    deguThe 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.

  • Iriarte-Diaz J, Bozinovic F and Vasquez RA (2006) What explains the trot-gallop transition in small mammals? J. Exp. Biol. 209: 4061-4066
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    Aerial locomotion

    Wing morphology 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.

  • Canals M, Iriarte-Diaz J, Olivares R and Novoa FF (2001) Comparison of the wing morphology of Tadarida brasiliensis (Chiroptera: Molossidae) and Myotis chiloensis (Chiroptera: Vespertilionidae) as representatives of two flight patterns. Rev. Chil. Hist. Nat. 74: 699-704
  • Iriarte-Diaz J, Novoa FF and Canals M (2002) Biomechanic consequences of differences in wing morphology between Tadarida brasiliensis and Myotis chiloensis. Acta Theriol. 47: 193-200
  • Canals M, Atala C, Grossi B and Iriarte-Diaz J (2005) Relative size of hearts and lungs of small bats. Acta Chiropt. 7: 65-72
  • Canals M, Grossi B, Iriarte-Diaz J and Veloso C (2005) Biomechanical and ecological relationships of wing morphology of eight Chilean bats. Rev. Chil. Hist. Nat. 78: 215-227
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    Maneuvering bat
    Flight maneuverability
    Flight maneuverability

    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.

  • Iriarte-Diaz J & Swartz SM (2008) Kinematics of the slow turning maneuvering in the fruit bat Cynopterus brachyotis. J. Exp. Biol. 211: 3478-3489
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    aerodynamic forces
    Effect of inertial forces on flight kinematics
    Effect of inertial forces on flight kinematics

    Figure caption: effect of wing motion on the body acceleration. If the center of mass (CoM) remains constant, the backward movement of the wings during the upstroke will produce an inertial acceleration (red arrow) that will move the body forward (blue arrow).

    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.

  • Iriarte-Diaz J, Riskin DK, Willis DJ, Breuer KS and Swartz SM (2011) Whole-body kinematics of a fruit bat reveal the influence of wing inertia on body accelerations. J. Exp. Biol. 214: 1546-1553
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    bat carrying a bird
    Effect of load-carrying on flight performance
    Effect of load-carrying on 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.


  • Iriarte-Diaz J, Riskin DK, Breuer KS and Swartz SM (in review) Kinematic plasticity during flight in fruit bats: individual variability in response to loading
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    Cranio-facial biomechanics

    Alligator mandible
    Strain and stress during feeding
    Helical axis
    3D jaw kinematics during chewing