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Session Schedule & Abstracts

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Saturday 2nd July, 2016

Hard-Tissue Biology 3

Room: Salon G   2:30 pm–4:00 pm

Moderator(s): Regnault S, Sartori J
HRD3-1  2:30 pm  Walking with giants: is the cortical bone structure and vascularization adapted to load bearing in large terrestrial vertebrates? Dumont M*, Uppsala University EBC, Department of Organismal Biology, Sub-department of Evolution and Development; Herrel A, UMR CNRS/MNHN 7179, Mecadev Adaptative mechanisms and evolution; Tafforeau P, European Synchrotron Radiation Facility; Sanchez S, Science for Life Laboratory and Uppsala University EBC, Department of Organismal Biology, Sub-department of Evolution and Development
Abstract: The cortical bone of long bones is perforated by vascular canals. This interconnected network is an integral component of the bone microstructure and undergoes continual change throughout life. Bone remodeling will affect the vascular organization, i.e. its size, volume and orientation. The external loads experienced by the long bones will shape the cortical microarchitecture. Sauropods are an ideal group to study this question because of their great body mass and late ontogenetic remodelling. We used propagation phase-contrast synchrotron microtomography to precisely characterize and quantify the vascular cortex organization of the long bones of sauropods in 3D. We compare the results to those obtained for extant and extinct large mammals. The vascular volume, orientation, and connectivity were used to understand the impact of growth and bone remodeling on bone integrity. Sauropods present in their early stages of development, a peculiar laminar vascular organization made of longitudinal “plates”. This organization is kept in periphery at the adult stage where a decrease of the cortical porosity goes along with a narrowing of the longitudinal plate and a consecutive enlargement of the radial canals. The late bone remodeling observed in adult sauropods results in a reduction of the canal size and generates a more tubular longitudinal architecture, similar to large mammals’ long bone. These vascular organizations are discussed in developmental and mechanical perspectives.

HRD3-2  2:45 pm  Patelloid and patellar sulcus: clues to kneecap evolution? Regnault S*, Royal Veterinary College; Pitsillides AA, Royal Veterinary College; Hutchinson JR, Royal Veterinary College
Abstract: The patella (kneecap) is a large sesamoid bone found within the patellar tendon. It has evolved independently at least three times: in mammals, birds, and lepidosaurs (lizards and kin). The presence of a fibrocartilaginous ‘patelloid’ in lieu of an ossified patella in many marsupials suggests a stepwise evolution; from tendon to cartilaginous ‘patelloid’ to ossified patella. It remains uncertain, however, whether other animals lacking an ossified patella might have a similar ‘patelloid’ soft tissue structure. Some older literature refers to a possible patelloid in the turtle Terrapene carolina and in an unspecified crocodilian, but these are isolated anecdotes. We have therefore sought to investigate how common such a structure might be – if widespread, it could infer that the patella is not truly independently evolved but commonly inherited in the form of the patelloid. Our studies also explore the relationship between the patella and intercondylar (patellar) sulcus of the femur. The sulcus is sometimes taken to infer presence of a patella/patelloid in incomplete fossils, providing valuable missing data with implications for the reconstruction of patellar evolution. We have dissected and sampled patellar tendons from several animals without ossified patellae, representing extant outgroups of those with patellae (turtles, e.g. Caretta caretta, Agrionemys horsfieldii; crocodylians, e.g. Osteolaemus, Melanosuchus, Caiman; lissamphibians, e.g. Salamandra salamandra, Ambystoma tigrinum). To date we have found no clear evidence of a soft tissue patelloid or cartilaginous modifications to the tendon in these other animals. Furthermore, we observed that several species with an ossified patella have a shallow sulcus, and conversely, some without the patella/patelloid have a relatively pronounced sulcus. Our data show that presence and depth of the patellar sulcus is not necessarily linked to patellar (or patelloid) presence.

HRD3-3  3:00 pm  The micro-structure, composition and mechanical properties of bones of the Olm (Proteus anguinus). Haggag L, The Hebrew University of Jerusalem; Jelic D, Croatian Institute of Biodiversity, Croatia; Shahar R*, The Hebrew University of Jerusalem
Abstract: The olm is an aquatic salamander that lives in dark, under-water caves in the limestone-rich areas of central Europe. The adult olm is fully adapted to total darkness, exhibits neoteny (retains larval features into adulthood) and impressive longevity (over 60 years). Not much is known about the material properties and micro-architecture of the olm skeleton. We present here results of our studies of the jaw bones, vertebrae and long bones of mature olms by micro-CT, light microscopy and electron microscopy, micro-indentation and thermo-gravimetric analysis.

HRD3-4  3:15 pm  Variation in limb bone stiffness between aquatic and terrestrial salamanders. Taft NK*, University of Wisconsin-Parkside; Kawano SM, National Institute for Mathematical and Biological Synthesis
Abstract: Salamanders have a generalized tetrapod Bauplan that has served as a popular model to study locomotion in context to the water-to-land transition in tetrapod evolution. Recent analyses have demonstrated that a terrestrial salamander, Ambystoma tigrinum, exhibited differential limb function that was associated with different biomechanical properties in the humerus and femur. Given that many basal tetrapods may have been largely or even exclusively aquatic, additional studies are needed to determine whether the material properties of bone also differ between the forelimb and hind limb in salamanders with different lifestyles. We explored whether the stiffness of the humerus and femur vary among aquatic versus terrestrial salamanders in the same genus. The axolotl, Ambystoma mexicanum, is exclusively aquatic throughout its life. Eastern tiger salamanders, Ambystoma tigrinum, are aquatic as juveniles but terrestrial as adults. In this analysis, we compared the stiffness of the femur and humerus among three groups: adult aquatic axolotls, large sub-adult aquatic tiger salamanders and adult terrestrial tiger salamanders. We used three point bending tests to measure the tangent Young’s modulus of elasticity, or bone stiffness, among these groups. The limbs of the terrestrial tiger salamanders had greater stiffness than the limb bones of both the aquatic axolotls and aquatic phase tiger salamanders, and the humeri were stiffer than the femurs across the three groups of salamanders. These results supported previous research that the humerus of the terrestrial tiger salamander had greater hardness values and higher safety factor against skeletal failure than the femur in this species. These results demonstrate how the stiffness of bones may correlate with the terrestrial capabilities of salamanders, potentially contributing new insights into the role of the forelimb and hind limb during the water-to-land transition in basal tetrapods.

HRD3-5  3:30 pm  Fiber courses of the Achilles tendon enthesis in the mouse (Mus musculus) as test for biomechanical hypotheses. Sartori J*, Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena; Köhring S, Fachgebiet Biomechatronik, Fakultät für Maschinenbau, TU Ilmenau; Schilling C, Fachgebiet Biomechatronik, Fakultät für Maschinenbau, TU Ilmenau; Witte H, Fachgebiet Biomechatronik, Fakultät für Maschinenbau, TU Ilmenau; Löffler M, Dresden Center for Nanoanalysis, TU Dresden; Fischer M S, Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena
Abstract: As a transition zone between the compliant tendon and the stiff bone an enthesis could be expected to be the weakest link in the force transmission chain between muscle and bone. At such an interface peak stresses can emerge from several phenomena: (1) forces due to tensile load and the resulting transversal contraction can sum up at the transition's margins. (2) Loads may concentrate in a part of the enthesis area, leaving another part of the tendon fibres relaxed due to an oblique orientation of the transition relative to the force vector. However, clinical evidence shows that entheses rather rarely cause failure of the muscle-tendon-bone chain. One explanation for their robustness is the “stretching brake model”: Fibers, which loop over cartilage chondrons, deform the chondrons, whenever the structure is stretched under tension. In this scenario the chondrons' material properties influence the stiffness of the transition zone – and could create a stiffness gradient by an increase in sphericity towards the bone. We scanned cell-macerated, demineralized and dried specimens of the mouse [C57BL/6J] Achilles enthesis in order to examine the fiber courses, and to test whether they fulfill the geometric requirements of this model. In the unmineralized fibrocartilage parallel fiber courses prevailed, their curvatures were mainly corresponding to the curvature of the complete tendon. Therefore we conclude that this macroscopic curvature of fibers in the unmineralized fibrocartilage is a major parameter for the recruitment of chondrons as stretching brake elements.

HRD3-6  3:45 pm  The remarkable armor of poachers. Summers A.P.*, University of Washington
Abstract: Poachers (Agonidae) are small, cold water fishes. They have no swim bladder, armor, and an unusual pit at the posterior margin of the skull. We have micro CT-scanned every genus of poacher with the aim of understanding the selective pressures that have led to the diversity of armor forms. In some species the armor is quite flat and unornamented, very much in line with medieval scale mail. In others the armor is ornate, with sharp spines, ridges and crenellations reminiscent of the baroque ceremonial armor. The armor serves at least two purposes in these fishes - it is protection from predation and also a source of sound production. There are constraints on the armor in that the fish must be able to swim, and therefore the armor must have some flexibility. Poachers swim primarily through pectoral fin oscillation, so this constraint may not be particularly strong, though there are other reasons it might be important to bend the body. Of particular interest is the amount of mineral in the armor versus the internal skeleton of the fish. In some species more than half the total mineral content is in the armor. The tubenose poacher (Pallasina barbata) is particularly interesting because this fish is the only poacher that swims up in the water column. It mixes with schools of tubesnouts (Aulorhynchus flavidus) and may be a useful model for how to lighten armor while maintaining effectiveness.

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