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Session Schedule & Abstracts

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Thursday 30th June, 2016

Locomotion 4

Room: Salon G   4:30 pm–6:00 pm

Moderator(s): Mayerl CJ, O'Donnell MK
LOC4-1  4:30 pm  Functional pelvic anatomy of the red-legged running frog (Anura: Hyperoliidae, Kassina maculata). Collings AJ*, The Royal Veterinary College; Porro LB, The Royal Veterinary College; Richards CT, The Royal Veterinary College
Abstract: While all frogs share a generalised body plan typified by a short body, elongate hindlimbs and reduced forelimbs, their pelvic anatomy is variable. Differences in muscle and ligament position, sacrum shape, and joint morphology are thought to allow different movements at the ilio-sacral joint to enable locomotor diversity among species. However, the biomechanical consequences of the various pelvic morphotypes and their associated motions remain unexplored. Specifically, morphotype 2A is associated with lateral rotation of the pelvis during walking. Although careful anatomical inspection and muscle activation data have led to inferences of pelvic function, we lack direct evidence regarding how the pelvic musculature causes lateral rotation. We combine gross dissection, I2KI enhanced microCT, and 3D kinematics data to model the propulsive roles of pelvic muscles of Kassina maculata, a walking specialist. Kinematic models based on data collected from N=3 frogs suggest the pelvis undergoes a mean peak to peak lateral excursion of 11.5 degrees throughout a stride. Additionally, we found bony and soft tissue anatomy consistent with the 2A pelvic type. The coccygeo-iliacus (CI) and coccygeo-sacralis both originate along the majority of the urostyle, inserting on the anterior two thirds of the iliac shaft and the bow-shaped sacrum respectively. The iliolumbaris (IL) also inserts onto the iliac shaft (lateral surface) anteriorly, having originated from five pre-sacral vertebrae. Both CI and IL thus act on the ilia, likely producing the lateral rotation of the pelvis when activated bi-laterally. Deeper analysis of microCT images will reveal muscle architectural details that, when combined with a biomechanical model, will allow estimation of muscle length changes. Further, this model can then be used to investigate how pelvic muscles contribute to walking by transmitting propulsive force to the limb and by modulating the actions of the femur.

LOC4-2  4:45 pm  The importance of good posture: clinging in climbing and non-climbing salamanders. O'Donnell M. K.*, University of South Florida; Deban S. M., University of South Florida
Abstract: Scansoriality has evolved multiple times in plethodontid salamanders. In the absence of claws or specialized toe pads common in other scansorial organisms, clinging and climbing on rough and smooth surfaces is likely achieved through gripping via the toes, adhesion of the skin surface, and in some species, by suction. In order to explore whether behavioral or morphological convergence enables access to vertical habitats, clinging performance was examined in multiple climbing and non-climbing species from nine genera within the Plethodontidae. Maximum cling angle, ranging from 0 through 180 degrees from horizontal, and functional adhesive surface area were quantified with a smooth, edge-illuminated acrylic sheet using frustrated total internal reflection. Significant variation in maximum cling angle was found among species, with some climbing and non-climbing species able to cling to 180 degrees from horizontal (i.e., upside down), and some species, including one arboreal species, unable to maintain clinging performance over 90 degrees. Variation in clinging performance on smooth surfaces could be accounted for by behavioral (i.e., postural) or morphological adaptations to increase functional adhesive surface area in relation to body mass, or by species-specific attachment mechanisms, such as increased skin stickiness or suction. Maintenance of cling performance over a wide range of body masses was observed in both the climbing Bolitoglossa and non-climbing species of Desmognathus; in many non-climbing species, clinging ability was strongly limited by functional surface area in relation to body mass. Variation in the minimum relative surface area necessary to maintain attachment suggested species-specific attachment mechanisms benefit climbing species and increase cling performance.

LOC4-3  5:00 pm  Scaling of morphology and performance in elastically powered systems. Olberding J.P.*, University of South Florida; Deban S.M., University of South Florida
Abstract: Individuals of a species may face the same selective pressures across a range of body sizes, so small and large individuals should be capable of similar absolute performance. Scaling of underlying morphology and physiology can determine scaling of locomotor performance. All else being equal, if limb muscle mass scales isometrically with body mass, then kinetic energy of a jump should be similar for individuals of all masses. Studies of frog muscles have found positive allometry of muscle velocity and power output with respect to body mass, leading to predictions of greater jump performance in more massive individuals. However, some frog species use stored elastic energy to power their jumps and often these systems amplify power beyond the capabilities of muscle alone. When using stored elastic energy, the velocity and power of muscle contraction do not influence performance thus performance should be the same for frogs of all sizes if all else scales geometrically. We tested this prediction in Cuban treefrogs using a 3D motion-capture system to quantify takeoff velocity and kinetic energy. We found that these measures of performance scale with positive allometry to body mass and snout-vent length despite the hypothesized unimportance of muscle velocity and power in an elastically powered system. These results suggest positive allometry in underlying muscle properties, particularly muscle mass and maximum force. Preliminary results from in vitro muscle experiments indicate positive allometry in mass and peak force of jumping muscles, suggesting that larger frogs are capable of doing relatively more muscle work and thus can achieve jumps of higher absolute performance compared to smaller frogs. Future experiments will test the prediction that the energy storage capacity of elastic tendons also scales with positive allometry to body mass to accommodate the relatively greater work done by larger individuals.

LOC4-4  5:15 pm  Hind limb muscle function in turtles: is novel skeletal design correlated with novel muscle function? Mayerl CJ*, Clemson University; Pruett J E, Clemson University; Rivera A R V, Creighton University; Blob R W, Clemson University
Abstract: Most vertebrates move extensively through their environment in order to find food, shelter, and mates. The capacity to perform such movements depends on a variety of factors, including the arrangements of the muscles that enable locomotion. Changes in muscle arrangement can have significant implications for locomotor performance, as a change in origination or insertion of a muscle can impact its line of action, and how well it performs a given movement. In pleurodire turtles, hind limb muscles that primitively originated on the pelvis have shifted to an origin on the shell, due to the derived fusion of the of pelvic girdle to the shell in this lineage. To test if the function of these muscles has also changed in relation to these positional rearrangements, we measured hind limb kinematics, muscle activity (EMGs), moment arms, and physiological cross sectional areas for aquatic generalist species of both pleurodire (Emydura subglobosa) and cryptodire (Trachemys scripta) turtles. We found not only that some hip muscles with differing attachments between taxa showed different patterns of activity, but also that some muscles with different attachments show similarities in muscle use. In cryptodires, puboischiofemoralis internus (PIFI) protracts the hip during swimming and walking, but in pleurodires it exhibits an additional burst during stance. Because the origin of PIFI has shifted ventrally to the shell in pleurodires, this additional burst could function in limb adduction or stabilization. In contrast, muscles such as the flexor tibialis internus retain similar muscle use profiles in both lineages, despite their changed origination in pleurodires. Our results suggest that, at least in turtles, a change in muscle origination can result in shifts in muscle function, but need not necessarily do so.

LOC4-5  5:30 pm  One foot out the door: limb function during swimming in a recently evolved, terrestrial lineage of turtles . Young VKH*, Clemson University; Vest KG, Clemson University; Rivera ARV, Creighton University; Espinoza NR, Clemson University; Blob RW, Clemson University
Abstract: Although aquatic lifestyles are considered ancestral among extant turtles, multiple lineages have become independently specialized for nearly exclusive use of terrestrial habitats, including the tortoises (Testudinidae) and the emydid box turtles (genus Terrapene). The extent to which swimming performance is retained in such lineages, despite terrestrial specialization, is unknown. Given that tortoises diverged from other turtles over 50 million years ago, but box turtles diverged from aquatic emydids only approximately 5 million years ago, we predicted that the swimming patterns of box turtles would more closely resemble those of their more aquatic relatives than those of tortoises. To test this prediction, we used high-speed video to compare limb kinematics during swimming in a flow tank across Russian tortoises (Testudo horsfieldii), eastern box turtles (Terrapene carolina), and two generalized aquatic emydid species: sliders (Trachemys scripta) and painted turtles (Chrysemys picta). Kinematic vector analyses indicated that the forelimb and hind limb showed different patterns of kinematic divergence across the species. For the forelimb, box turtles show kinematic profiles most similar to those of tortoises for four out of five variables; in contrast, for the hind limb, box turtles show kinematic profiles most similar to sliders or painted turtles for four out of five variables. These results suggest that terrestrial specialization may have impacted forelimb function more than hind limb function in box turtles, emphasizing the different roles that these limbs play in meeting locomotor demands.

LOC4-6  5:45 pm  The effects of differential function in the limbs of turtles on patterns of symmetry: an examination of fore- and hindlimb propelled species. Rivera G*, Creighton University
Abstract: Understanding how selective forces influence patterns of symmetry remains an active area of research in evolutionary biology. One hypothesis, which has received relatively little attention, suggests that the functional importance of morphological characters could influence patterns of symmetry. Specifically, it posits that features with greater functional importance should be more symmetrical. The aim of my research was to examine the patterns of fluctuating asymmetry (FA) present in the limb bones of turtles, focusing on two specific groups: freshwater turtles (family Emydidae) and marine turtles (family Cheloniidae). Emydid turtles primarily employ a hindlimb-dominant swimming style, whereas cheloniid turtles employ a forelimb-dominant swimming style. This dichotomy in propulsive modes provides an excellent test of the biomechanical hypothesis of symmetry. I measured the length of the proximal limb bone of the left and right fore- and hindlimbs (humerus and femur) of several emydid species. I also collected data from the hindlimbs of multiple cheloniid species. These data were used to calculate asymmetry (FA) in each set of bones for each species. I then used these data to test two predictions. First, I tested whether within emydid turtles, the hindlimbs (primary propulsor) would display greater symmetry than the forelimbs (secondary propulsor). Second, I tested whether the hindlimbs of emydid turtles (hindlimb dominant) were more symmetrical than the hindlimbs of cheloniid turtles (forelimb dominant). Preliminary data indicate that within emydid turtles, symmetry is always higher in hindlimbs. Thus, with the biomechanical hypothesis supported in emydid turtles, determining whether the major locomotor change found in cheloniids (reversal of the primary propulsor) is accompanied by decreased levels of hindlimb symmetry (relative to emydids) is an important second test of the ability of natural selection to drive evolutionary changes in symmetry.

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