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Session Schedule & Abstracts




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Thursday 30th June, 2016

GEN2
General Morphology 2

Room: Salon C   11:30 am–1:00 pm

Moderator(s): Bouilliart M, Paluh DJ
GEN2-1  11:30 am  Morphology of the ovarian germinal epithelium in bony fishes: Centropomidae Centropomus undecimalis, Goodeidae Xenotoca eiseni and Chlorophthalmidae Chlorophthalmus agassizi. Grier HJ*, Florida Fish and Wildlife Conservation Commission, Florida Fish and Wildlife Research Institute, St. Petersburg, Florida. Department of Vertebrate Zoology, Division of Fishes, National Museum of Natural History, MRC 159, Smithsonian Institution, Washingto; Uribe MC, Laboratorio de Biología de la Reproducción Animal. Departamento de Biología Comparada. Facultad de Ciencias, Universidad Nacional Autónoma de México. México; Parenti LR, Department of Vertebrate Zoology, Division of Fishes, National Museum of Natural History, MRC 159, Smithsonian Institution, Washington, DC   harry.grier1@verizon.net
Abstract: The female germinal epithelium was examined in three species of distantly related teleosts. In C. undecimalis, X. eiseni and C. agassizi, the germinal epithelium lines the ovarian lumen and is composed of epithelial cells within which are scattered, and widely separated oogonia and cell nests. The process of folliculogenesis is precisely the same in all three species. The germinal epithelium is supported by a basement membrane that separates it from stroma. In similar fashion, during folliculogenesis, the germinal epithelium basement membrane is extended to surround individual follicles, separating them from stroma from which the theca forms. Therefore, the theca is not part of the follicle. Rather, the follicle and its encompassing theca, represent cells derived from two different tissue compartments that comprise a follicle complex. An ovarian follicle is simply the oocyte and its encompassing follicular cells. In all three species, epithelial cells from the germinal epithelium become prefollicle cells during folliculogenesis and then follicle cells when the forming follicle is completely surrounded by a basement membrane, marking the completion of folliculogenesis. After ovulation, a postovulatory follicle (POF) remains within the ovarian lamellae and is composed of just the former follicle cells. The postovulatory follicle is encompassed by a basement membrane and a postovulatory theca (POT). Together, POF and POT compose a postovulatory follicle complex (POC).

GEN2-2  11:45 am  Comparison of cranial development of Siberian sturgeon, Acipenser baerii, and Russian sturgeon, Acipenser gueldenstaedtii (Acipenseriformes: Acipenseridae). Warth P*, University of Jena; Konstantinidis P, Virginia Insitute of Marine Science; Hilton E J, Virginia Institute of Marine Science; Naumann B, University of Jena; Olsson L, University of Jena   peter.warth@uni-jena.de
Abstract: The development and evolution of the vertebrate head has been studied a great deal throughout the history of morphology. Still, there are gaps in our fundamental knowledge that can be filled through renewed study of exemplar taxa using modern approaches to morphology. Here we study the morphogenesis of the cranial and pectoral girdle skeleton in two species of sturgeons, Acipenser baerii and A. gueldenstaedtii, which both show a generalized sturgeon phenotype and are readily available through hatcheries. Closely staged ontogenetic series of these species showing the development of the neuro-, viscero- and dermatocranium were analysed and compared. Sturgeons (Acipenseridae), together with the paddlefishes (Polyodontidae), belong to the order Acipenseriformes and have a phylogenetic position close to the base of the Actinopterygii. This makes them a valuable group to study in the large-scale evolutionary context of osteichthyan vertebrates. Furthermore, resolving the phylogeny within Acipenseridae calls for additional molecular as well as morphological data. Ontogeny is a rich source of information for phylogenetic analyses and in this study we provide a baseline for future comparative phylogenetic studies. Our results show an early development of neurocranial elements, starting with the trabeculae cranii and the parachordal cartilages, followed by the otic capsule and the mandibular arch elements. The elements of the hyoid arch appear simultaneously with elements of the first branchial arch. The posterior branchial arches follow subsequently. The branchial arches are patterned in a ventral to dorsal direction. The first bony elements appear in the mandibular arch. Teeth are formed and later reduced in an antero-posterior direction, on the dentary, dermopalatine, palatopterygoid and on tooth plates in the buccal cavity. Closure of dorsal fenestrae of the neurocranium and ossification of overlying dermatocranial elements occur relatively late.

GEN2-3  12:00 pm  Comparative beak morphology of two subspecies of Australian Red-tailed Black-Cockatoos: Small changes with significant functional effects as a model for macroevolutionary processes. Homberger D.G.*, Louisiana State University, Baton Rouge   zodhomb@lsu.edu
Abstract: A comparison of the beak morphology and feeding behavior of two Red-tailed Black-Cockatoos served as a natural experiment to model evolutionary changes in adaptation to particular environments and foods. The eastern population of Calyptorhynchus banksii samueli feeds mainly on seeds in hard woody fruits of forbs in arid open woodlands of northwestern New South Wales. Its psittacid beak is characterized by an upper bill tip that overhangs the lower beak and whose internal surface is rough with a transverse step, in which the transverse cutting edge of the lower beak fits. It cracks open fruits between the transverse step of the upper beak and the cutting edge of the lower beak. C. b. graptogyne feeds mainly on seeds in complex fibrous-woody eucalypt capsules in Gondwanan forest refugia in southeastern South Australia and northwestern Victoria. Its calyptorhynchid beak is characterized by (1) a short upper bill tip that is apposed to the gonys of the lower beak and whose internal surface is smooth without a step, and (2) an emarginated v-shaped transverse edge of the lower beak. It tears apart fruits with the upper bill tip while the tongue and lower beak move sideways and back-and-forth to position the fruit for the upper beak’s actions. This multi-step feeding mechanism requires dexterity that must be learned and practiced by fledglings for months. It also depends on the exceptionally dense touch receptors in the beak and tongue of Psittaciformes in general. During the drying of Australia separating from Gondwana, the selection of minor changes in surface structures of the calyptorhynchid bill resulted in a psittacid bill with a fundamentally different feeding mechanism to exploit changed food sources. This scenario exemplifies how minor structural changes can have fundamental effects that set the stage for further modifications leading to what are perceived as macroevolutionary events. Supported by NSF and LSU Foundation “Morphology of Birds”

GEN2-4  12:15 pm  Evolution of cornification in amniotes: the case of Sauropsids. Alibardi L*, Comparative Histolab, Padua, Italy   
Abstract: During the adaptation of the integument to terrestrial conditions in amniotes an efficient stratum corneum was originated through the evolution of numerous corneous proteins in addition to the framework of (alpha-)keratins forming the intermediate filaments of keratinocytes. The new genes for corneous proteins such as involucrin, loricrin and filaggrin evolved in a chomosome region indicated as Epidermal Differentiation Complex (EDC), a locus with no relationship to keratin genes. The addition of EDC proteins to alpha-keratins transformed the prevalent epidermal keratinization of anamniotes into a widespread new process of terminal differentiation known as cornification in the epidermis but more accentuated in appendages such as hard scales, claws, hairs and feathers in amniotes. In Sauropsid amniotes among other EDC proteins a unique type of small proteins of 10-24 kDa evolved a central region of 34 amino acids conformed as beta-sheets that, differently from the other EDC proteins, allowed the formation of long polymers of filamentous proteins customarily termed beta-keratins. To the initial beta-sheet core of these new Corneous Beta Proteins specific N- and C-regions were later added in different lineages of sauropsids in relation to the evolution of specific epidemal adaptations and appendages, such as claws, shell in turtles, adhesive pads in some lizards, and feathers in birds. The presentation stresses the evolution of the process of cornification as an extension of the general process of keratinization.

GEN2-5  12:30 pm  Comparative morphology of the quadrate bone within Gekkota (Squamata): Phylogenetic and functional implications. Paluh DJ*, Villanova University; Bauer AM, Villanova University   dpaluh14@jcu.edu
Abstract: The functional components of the reptile skull are divided into the chondrocranium, dermatocranium, and lower jaw. These regions are interconnected and become operational through the quadrate: a bone vital for cranial biomechanics and support of the auditory system. The quadrate is a very complex and variable structure in squamates; however, the comparative anatomy of this element has never been studied in detail. We investigated the diversity of quadrate morphology within geckos (117 of 125 genera examined) using high-resolution x-ray micro-computed tomography and cleared and double-stained specimens. Our objectives were to 1) quantify quadrate shape using three-dimensional geometric morphometrics and 2) investigate the interactions of phylogeny, function, and allometry influencing quadrate morphology using comparative methods. Our results demonstrate substantial variation in quadrate morphology across gecko species. Carphodactylids and pygopodids each possess uniquely derived quadrate morphologies, while the remaining gecko families retain extensive overlap in quadrate shape. All carphodactylid taxa, as well as one gekkonid and diplodactylid, possess broad and laterally expanded quadrates, and we hypothesize this is a functional modification that has evolved to support enlarged adductor mandibulae musculature. Three miniaturized pygopodid genera have reduced or lost the external auditory meatus and tympanic membrane, and this modification has resulted in the reduction of the posterior concavity and tympanic crest of the quadrate. Lastly, miniaturized taxa in four families possess elongate, slender quadrates, suggesting a strong influence of allometric scaling. Therefore, our study has identified the disparity of quadrate morphology within geckos and has highlighted the importance of considering multiple processes that may influence the diversification of phenotypic characters.

GEN2-6  12:45 pm  Musculoskeletal systems simplified to 2D and 3D biomechanical models: the potentials and limitations of modeling bite forces. Bouilliart M*, Ghent University; De Meyer J, Ghent University; Van Wassenbergh S, Ghent University; De Kegel B, Ghent University; Adriaens D, Ghent University   mathias.bouilliart@ugent.be
Abstract: In case the bite force of an organism can’t be measured in vivo, it can be estimated mathematically using static-state equilibrium models. Although this approach will always simplify reality, several models presently exist that exhibit different levels of simplifications of the musculoskeletal topography and the parameters describing muscle physiology. To investigate the impact of such simplifications, three frequently used models are compared in this study. The first model calculates bite forces by projecting all lever arms and the muscle’s line-of-action onto the mid-sagittal plane of the specimen. Muscle force is based on the muscle’s PCSA and therefore remains constant throughout the simulation of different gape angles in this model. The second model is comparable to the previous model, but describes the specimen’s musculoskeletal topography using 3D-coordinates of the muscles and levers. The third model again uses these 3D-coordinates, but calculates muscle contraction force based on a series of parameters (including fiber and tendon lengths and pennation angle) and physiological characteristics (including F-L and F-V relationships, activation rise time and passive elasticity). As the lower jaw becomes depressed, this model accounts for changes in muscle parameters according to this movement. Input-data for these models is obtained from a European yellow eel specimen (Anguilla Anguilla). Several allometric-scaled morphs, testing the effects of changes in skull width, lever arms and muscle-length, are implemented in the models as well. Model results visualize the effects of different muscle orientations on the same lever, of 2D versus 3D (2D overestimates forces), of constant versus variable muscle contraction force (changing output profile), and of increasing the head width. Therefore, these comparisons allow defining constraints on the predictive power of different models generally used to calculate bite forces.



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