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Session Schedule & Abstracts

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Thursday 30th June, 2016

General Morphology 1

Room: Salon C   9:30 am–11:00 am

Moderator(s): Cernansky A, Ward AB
GEN1-1  9:30 am  Homology of the accessory elements of the hyoid arch within Gnathostomata. Bockmann F. A., Universidade de São Paulo, FFCLRP; Carvalho M., Universidade de São Paulo, Instituto de Biociências; Carvalho M. R., Universidade de São Paulo, Instituto de Biociências; Rizatto P. P.*, Universidade de São Paulo, FFCLRP
Abstract: In this study, we investigated specifically the homology of the accessory elements of the hyoid arch, called symplectic and inter-hyal, by means of anatomical comparisons among chondrichthyans and actinopterygian polypteriforms, acipenseriforms, lepisosteiforms, amiiforms, and some teleosteans at different stages of their early ontogenies, both extant and fossil. The symplectic belongs to the epal series, being articulated with the distal extremity of hyomandibula whereas the interhyal is part of the ceratal series, being usually attached to the distal extremity of ceratohyal. Recently, it has been suggested that a cartilagious piece lying between the distal tips of ceratobranchials 4 and 5 of actinopterygians, which was usually identified as epibranchial 5, is actually an accessory element associated with ceratobranchial 4. The origin of this element may have a single origin, being a remnant of a series of elements distally attached to ceratobranchials 1–4, a condition totally or partially retained in basal actinopterygians. A closer examination of the anatomy of the osteichthyan hyoid and branchial arches suggests that primitively there are actually two accessories elements in each arch, an anterior, which is associated to epal portion of the arch, and a posterior, which is attached to the ceratal portion. According to this finding, it is proposed that the symplectic is serially homologous to the anterior, epal accessory elements of the branchial arches, which are characteristically present in Polypteriformes and Lepisosteiformes, while the inter-hyal would be serially homologous to the posterior, ceratal accessory elements of the branchial arches, which are more commonly encountered among actinopterygians (including the accessory element of ceratobranchial 4). This work is supported by CNPq and FAPESP.

GEN1-2  9:45 am  Evolution of complex skull shape across the global radiation of extant bats. Shi JJ*, University of Michigan; Rabosky DL, University of Michigan
Abstract: Biological shapes and structures are intrinsically linked to an organism's ecological niche, their performance and function, and their integration or modularity within a morphological whole. Many biological shapes are highly complex and multidimensional, making them difficult to model within the framework of established evolutionary theory. Much research on adaptive radiations and macroevolution have proposed that rates of trait evolution are variable through time—clades can be marked by an initial, explosive exploration of trait space, followed by gradual deceleration through time as niche space is claimed by congeners and competitors. Using both traditional and geometric morphometric data, we explore this and related hypotheses during the global radiation of extant bats (Order Chiroptera). Bats are among the most ecological and morphologically diverse mammals, and their skulls are known to exhibit a tight coupling among morphological shape, performance, and ecology. Using a comprehensive dataset that spans skulls from all extant bat families, and a recent, time-calibrated phylogeny of the order, we quantify shape disparity across bats, calculate rates of trait evolution, and explore the trajectory of shape evolution through time. We find a decoupling between rates of trait evolution and speciation, but also that macroevolutionary patterns are both module- and clade-dependent.

GEN1-3  10:00 am  Mammalian neck construction between variation and constraints. Arnold P.*, Institut fuer Spezielle Zoologie und Evolutionsbiology mit Phyletischem Museum, Friedrich-Schiller-Universität Jena, Germany; Stark H., Institut fuer Spezielle Zoologie und Evolutionsbiology mit Phyletischem Museum, Friedrich-Schiller-Universität Jena, Germany; Lehrstuhl für Bioinformatik, Friedrich-Schiller-Universität Jena, Germany; Werneburg I., Senckenberg Center for Human Evolution and Palaeoenvironment (HEP) at Eberhard Karls Universität Tübingen, Germany; Fachbereich Geowissenschaften der Eberhard Karls Universität Tübingen, Germany; Museum für Naturkunde, Leibniz-Institut für Evolutions- & B; Fischer M. S., Institut fuer Spezielle Zoologie und Evolutionsbiology mit Phyletischem Museum, Friedrich-Schiller-Universität Jena, Germany
Abstract: Neck construction in mammals is highly determined by developmental (e.g. fixed number of cervical vertebrae) and gravitational (e.g. permanent head bending moment) constraints limiting the possibility for adaptive modifications through evolution. However, there exist obvious differences in neck morphology between, for example, small and large, terrestrial or fossorial, upright, jumping, and high browsing mammals which correspond to different functional demands. As positional (i.e., local) identity of the individual vertebrae seems to be highly conserved and invariant across mammals, the extent of the observable evolutionary variation is not yet clear. We analyzed and quantified patterns of variation and conformity of neck morphology across mammals by combining different approaches on osteological and myological data. Cervical scaling parameters and proportions were measured across a variety of species representing all major monotreme, marsupial, and placental groups in order to infer global characteristics of cervical spine variation. In contrast, muscular properties were examined in situ based on contrast enhanced µCT-scanning for different small mammals representing so called generalized members of their clades. Our results imply that overall neck construction is guided by a fixed set of constructional principles common to all mammals. However, deviation from those ‘rules’ evolved in several lineages on different constructional levels (cervical scaling, vertebral proportion, muscular topography, and micro-architecture). Although limited in their extent, the combination of these deviations enables the mammalian neck for constructional variation and adaptive modification beyond its constraints.

GEN1-4  10:15 am  How does the transition from lizard body to serpentiform morphology influence the atlas-axis complex in lizards? . Cernansky A.*, Comenius University in Bratislava
Abstract: Currently, the minimal understanding of comparative anatomy on the neck region represents a significant knowledge gap in understanding these anatomical structures as a whole. The comparative vertebral morphology of the atlas-axis complex in cordyliforms, xantusiid and several skinks is reported here. These lizards are particularly interesting because of their different ecological adaptations and anti-predation strategies, where conformation ranges from the lizard-like body to a snake-like body. This transition to serpentiform morphology shows several evolutionary patterns in the atlas-axis complex depending on the stage of the transition and ecology of animals (e.g., adaptation to burrowing lifestyle or for rapid surface mobility). Morover, the first intercentrum of African Chamaesaura and Tetradactylus africanus (serpentiform grass-swimmers) is fully curved anteriorly, underlying the occipital condyle. While this limits ventral skull rotation beyond a certain angle, it locks the skull, which is a crucial adaptation for a sit-and-wait position in grassland habitats that needs to keep the head stabilized.

GEN1-5  10:30 am  Tinkering with the tail: variation in the vertebral column in Ophidiiformes. Ward A. B.*, Adelphi University; Galloway K. A. , University of Rhode Island; Porter M. E., Florida Atlantic University; Mehta R. S., University of California Santa Cruz
Abstract: Within Actinopterygii, body elongation is the dominant axis of shape variation. Most often, body elongation involves modification to the postcranial axial skeleton, either through adding additional vertebrae or lengthening the vertebral centra. In this study, we examine the vertebral column and body shape of members of the group, Ophidiiformes (cusk eels, brotulas, and pearlfishes). Ophidiiform fishes vary in their degree of elongation, which may be tied to their diverse ecologies. An interesting attribute of elongation in these fishes is a strong tapering caudal region; the degree of tapering also varies across species. Since caudal fin size has been linked to swimming performance, it is likely that extreme body tapering will result in a decrease of propulsive power during swimming. Our goal is to examine how morphological variation in body shape and vertebral column morphology in the caudal region may affect swimming performance. We measured 13 morphological and meristic variables from vertebrae and body shape (e.g., centrum height and length) in 14 species. We tested the relationship between decrease in body depth and centrum height (tapering) and found that while nine species have similar tapering in the body and vertebral column, there are five species, which have more tapering in the body than the vertebral column. Ophidiiformes are highly variable in the decrease in centrum height and length along the caudal region. When controlling for vertebral number, we found that the second moment of area (I) decreased along the caudal region. While I decreases posteriorly along the caudal region for all members of the group, Brotula sp., with the most extreme tail tapering, had the lowest rate of decline of I. Chilara taylori had the greatest I, indicating relatively stiff posterior vertebrae. This study provides a model for examining how changes to the caudal vertebrae associated with tail tapering might affect the ecology of fishes.

GEN1-6  10:45 am  Body shape transformation along anatomical lines of least resistance in labyrinth fishes. Collar D*, Christopher Newport University; Ward A, Adelphi University; Mehta R, University of California, Santa Cruz
Abstract: Body shape transformations punctuate vertebrate evolutionary history. Eel-like forms and torpedo-shaped bodies evolved within ray-finned fishes; elongate limbless forms arose within lissamphibians; and snakes and snake-like lizards evolved within squamates. Previous researchers have shown that varying combinations of changes to dimensions of the body, axial skeleton, and skull can drive transformations in different lineages. But why has a particular transformation involved change in some body regions but not others? Here, we test the hypothesis that the anatomical changes underlying morphological transformation are shaped by constraints that are shared with closely related lineages. In labyrinth fishes (Anabantoidei), we identified rapid evolution from a relatively deep-bodied ancestor to a torpedo-shaped body in the pikehead (Luciocephalus pulcher and L. aura). We then developed a novel method to compare the combination of anatomical changes leading to the pikehead with the major axis of anatomical diversification in other anabantoids. We found that the pikehead form results from exaggerated changes in the same anatomical features that drive shape variability across all anabantoid fishes. These results reveal a common anatomical basis for body shape diversity that is taken to the extreme in the evolution of the pikehead form.

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