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Session Schedule & Abstracts

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Thursday 30th June, 2016

Locomotion 3

Room: Salon G   2:30 pm–4:00 pm

Moderator(s): Diamond KM, Flammang BE
LOC3-1  2:30 pm  The gibbon’s Achilles tendon revisited. Aerts P*, University of Antwerp; D'Août K, University of Liverpool; Berillon G, CNRS; Thorpe S, University of Birmingham; Vereecke E, University of Leuven
Abstract: Among great apes (Hominidae), only humans have a well-developed Achilles tendon. This is generally interpreted as an adaptation for energy storage and recoil during cyclic locomotion. The premised basic condition, a short external tendon in favour of long fibered triceps surae muscles, is found in all extant non-human great apes, and therefore probably precedes the last common ancestor of Hominidae. Providing a large Range of Motion, this morphology is thought to be beneficial for locomotion in a complex arboreal habitat. Lesser apes (Hylobatidae), however, also have well-developed long Achilles tendons. Despite their arboreal lifestyle, these species frequently perform bipedal ‘grounded running’. As such, it’s tempting to suggest that the gibbon’s Achilles tendon represents an adaptation for an economical bouncing gait, too. Several aspects of the functional anatomy of the triceps surae seem to support this view, but the compiled evidence is not entirely convincing. We revisit and integrate all our data on hylobatids (anatomy, kinematics, inverse dynamics, material properties) and conclude that the percentage energy return from the Achilles tendon is limited, and may even come at an extra cost. Inertial reduction or catapult action may be forwarded as alternative adaptive explanations. However, we want to offer a new perspective. Based on the available information, cercopithecids, sister group of the apes, also seem to possess well developed Achilles tendons. It is therefore not improbable that this represents the basic condition also present in the last common ‘Cercopithecoidea-Hominoidea’ ancestor. The Achilles tendon would thus be retained as a relict (‘no harm – no benefit’) in the brachiating gibbon, whereas its energy saving potential could have further been exploited in the evolutionary lineage towards human terrestrial bipedalism. If true, the common non-human great ape triceps surae anatomy should represent convergent evolution.

LOC3-2  2:45 pm  Loading distribution over the four fingers of the tapir during locomotion . Nauwelaerts S*, Univ. Antwerpen; Vangeel K, Univ. Antwerpen; MacLaren J, Univ. Antwerpen; Aerts P, Univ. Antwerpen
Abstract: The tetradactyl equid ancestor has evolved into a monodactyl modern horse (Equus). In order to create realistic models simulating equid ancestor locomotion, a reliable model that would predict how the ground reaction forces would be distributed over the fingers is necessary. We chose the tapir (Perissodactyla: Tapirus), which has retained the tetradactyl state in its forelimb, as a model species. We used a pressure mat to measure plantar pressures during walk in four species of tapir, with 3 to 5 representatives of each species. A Matlab program calculated the total load on each finger for each trial based on total pressure and total area underneath each finger. The load underneath the foot pad was also determined. Speed was taken into account by digitizing the stride length and duration on the corresponding videos. Surface scans for the appropriate species were made for the four metacarpals from museum specimens. Maximal stress was calculated in a FEBio v2.4. Four hypotheses on load distribution were tested. Loads were expected to either be proportional to metacarpal length or inversely proportional to the stress caused by a constant load. A third hypothesis was based on a possible prevention of sinking in the compliant substrate by testing whether the mean and maximal pressure differed between the four toes. Finally, the last hypothesis correlated the distances from the center of the pressure for each finger to the total center of pressure path based on the summed pressures over time to test whether finger configuration determined load distribution. The first three hypotheses on the load distribution over the fingers were rejected. With increasing speed, the load was shifted more towards the foot pad, hereby avoiding overloading the fingers. The last hypothesis was partially confirmed. These results will be discussed with respect to general rules regarding predicted load distributions in animals for which only osteology is available i.e. fossil taxa.

LOC3-3  3:00 pm  Walking with giraffes – joint angles, moments and effective mechanical advantage. Basu C*, Royal Veterinary College; Hutchinson JR, Royal Veterinary College
Abstract: Giraffes (Giraffa camelopardalis) are ruminant artiodactyls that possess extreme body proportions, whilst maintaining a large body mass. This morphology (for example long limbs), is expected to have functional consequences on aspects of locomotion, such as joint angles in the limb, joint moments and effective mechanical advantage. We measured ground reaction forces and synchronized kinematics of over 100 walking strides from three adult reticulated giraffes in a zoological park. The giraffes walked at a preferred speed of 0.96 m/s, with a mean stride length of 2 metres, and mean stride frequency of 0.5 Hz. We documented musculoskeletal geometry and measured muscle architecture from the dissection of a different, but similar sized adult male giraffe, weighing 880 kg. The muscles with the largest physiological cross-sectional areas in the forelimb and hindlimb were M. triceps brachii (0.042 m2) and M. vastus lateralis (0.022 m2), respectively. The longest musculotendon unit in the forelimb was the common digital extensor (1.75 m), and in the hindlimb the lateral digital extensor (1.5 m). We combined these data to create a dynamic 3D musculoskeletal simulation of locomotion, using this model to estimate muscular moment arms and effective mechanical advantage of individual joints across the stride, and compare this with other animals of extreme size.

LOC3-4  3:15 pm  Impacts of stream velocity and prey morphology on predator-prey interactions in Hawaiian stream fishes. Diamond KM*, Clemson University; Schoenfuss HL, Saint Cloud State University; Walker JA, University of Southern Maine; Blob RW, Clemson University
Abstract: There are five amphidromous gobiid fishes endemic to the Hawaiian Islands. The only piscivorous species among the five, Eleotris sandwicensis, resides in estuaries where it preys on juveniles of the other four species as they migrate upstream. However, the strength of stream flow through which juveniles migrate can vary substantially, and the impact of such flow variation on aquatic predator-prey interactions has had limited study in any system. Using a combination of flow tank experiments and in-stream video collection, we collected data to address the following questions: (1) Does ambient flow inhibit the detection of predators? (2) For fish that respond to attack stimuli in flow, does body shape impact escape behavior? (3) Do predators take advantage of potential masking of stimuli that they impose on prey? We found that juveniles from the prey species showed a reduced frequency of response to attack stimuli that came from the same direction as ambient flow. However, fish that did generate an escape response when attacked in line with stream flow escaped at higher angles compared to fish attacked perpendicular or opposite to the direction of stream flow. Body shape did not impact escape angle but, contrary to expectations, peak accelerations were higher for fish with more streamlined bodies rather than deeper bodies under certain flow conditions. Preliminary results of in-stream video observation suggest a trend that matches our flow tank trial results, with juvenile gobies that were attacked cranially (as they migrate upstream) exhibiting larger escape angles than fish attacked more caudally. Understanding how flow impacts predator prey interactions is important for many aquatic systems, particularly those that are prone to frequent changes in flow speed. This system exemplifies how environmental selection pressures can interact with biotic selection pressures to impact behavior and survival during predator-prey interactions.

LOC3-5  3:30 pm  Waterfall-climbing performance of gobiid fishes from La Réunion: how conservative are novel functional behaviors? . Schoenfuss HL*, St. Cloud State University; Bertram RS, St. Cloud State University; Lagarde R, Hydrô Réunion ; Ponton D, UMR Entropie; Diamond KM, Clemson University; Offerle T, Clemson University; Blob RW, Clemson University
Abstract: Several species of gobiid fishes from oceanic islands have evolved the ability to climb tall waterfalls. This behavior is most common among juveniles that are returning to adult stream habitats after completing a marine larval phase, and is facilitated by the fusion of the pelvic fins (in all gobies) into a ventral sucker. Previous observations identified two distinct modes of climbing. “Powerbursting” is found in many species and is likely the ancestral mode, with climbing powered by brief bouts of axial undulation between periods of attachment to the substrate. In contrast, “inching” is known only in the genus Sicyopterus, and is executed through alternating attachment of the pelvic sucker and a novel oral sucker. Comparisons among powerbursting species from Hawai’i and the Caribbean have shown a wide range of performance within this climbing mode; however, inching performance has only been measured in one species, S. stimpsoni from Hawai’i. To evaluate whether inching species might show less diversity in performance than powerburst climbers due to the more recent evolution of inching, or the demands of oral-pelvic coordination, we filmed climbing by two additional species from the Indian Ocean island of La Réunion: the inching climber S. lagocephalus, and the powerburst climber Cotylopus acutipinnis. For inching S. lagocephalus, climbing speed and the percentage of time spent moving closely matched previous results from S. stimpsoni; however, C. acutipinnis showed reduced climbing performance that differed from that measured in other powerburst species. Thus, the novel evolution of inching may restrict gobies to a more conservative range of climbing performance than powerburst mechanics.

LOC3-6  3:45 pm  Tetrapod-like pelvic girdle in a walking cavefish. Flammang BE*, NJIT; Suvarnaraksha A; Markiewicz J; Soares D
Abstract: Fishes have adapted a number of different behaviors to move out of the water, but none have been described as being able to walk on land with a tetrapod like gait. Here we show that the blind cavefish Cryptotora thamicola walks and climbs waterfalls with a salamander-like lateral sequence gait and has evolved a robust pelvic girdle that shares morphological features associated with terrestrial vertebrates. In all other fishes, the pelvic bones are suspended in a muscular sling or loosely attached to the pectoral girdle anteriorly. In contrast, the pelvic girdle of Cryptotora is a large, broad puboischiadic plate that articulates with a hypertrophied sacral rib; fusion of these bones in tetrapods creates an acetabulum. The vertebral column in the sacral area has large anterior and posterior zygapophyses, transverse processes, and broad neural spines, all of which are associated with terrestrial organisms. The gait kinematics of Cryptotora walking up 45 and 90 degree inclines are described as a lateral sequence gait with the axial body following a standing wave. These findings are significant because they represent the first example of behavioural and morphological adaptation in an extant fish that converges on the tetrapodal walking behaviour and morphology.

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