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Session Schedule & Abstracts

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Thursday 30th June, 2016

Sensory Biology & Neuroscience 2

Room: Salon F   11:30 am–1:00 pm

Moderator(s): Schmitz L, Stoessel A
SBN2-1  11:30 am  Adaptive signals in the morphological evolution of vertebrate eyes. Schmitz Lars*, Claremont Colleges
Abstract: The morphology of vertebrate eyes often seems to match the visual requirements imposed by the photic environment of the organism. In particular the preferred activity time in the 24 hour cycle (diel activity pattern) is considered to strongly influence the morphological evolution of eyes. For example, the eyes of night-active (nocturnal) organisms often feature traits consistent with improved light sensitivity, whereas eye shape of day-active (diurnal) organisms tends to reflect bright light levels. Even though empirical data strongly point towards adaptive evolution as the underlying mechanism producing the observed patterns, rigorous analyses of the tempo and mode of evolution are rare. Using the R-package SLOUCH and time-calibrated phylogenies, I characterized the phylogenetic half-life and stationary variance of visual performance features in three different vertebrate clades. Two of the investigated clades represent avian radiations (Strisores, n=59 sampled species; Afroaves, n=74), whereas the third clade is mammalian (Euarchontoglires, n=109). All clades feature a large diversity of diel activity patterns (nocturnal, diurnal, as well as day/night or twilight activity, grouped as cathemeral/crepuscular) and multiple evolutionary trait reversals, making them ideal for studying adaptive evolution. In the presence of strong selection, phylogenetic half-life (time to evolve half the distance from an ancestral state towards the optimum of a novel selective regime) and stationary variance (tendency to deviate from the optimum) are expected to be low, whereas both phylogenetic half-life and stationary variance may approach infinity when non-selective mechanisms are prevalent. My results suggest strong selection on eye shape evolution in both bird clades, whereas selection is much reduced in mammals. It is possible that non-visual senses are more important for fitness in mammals and hence weaken the functional constraint on eye shape evolution.

SBN2-2  11:45 am  Drivers of visual field evolution in mammals. Fraser D. L.*, Smithsonian National Museum of Natural History; Webster R. J., Carleton University; Herman A., Carleton University
Abstract: Mammals have highly varied visual systems, which is likely due to the extraordinary diversity of their ecological niches. Among mammals, visual field overlap, measured as orbital convergence, varies from a high degree of convergence (i.e. binocular vision) to the non-overlap of visual fields (i.e. panoramic vision). Three primary hypotheses have formed the basis of understanding visual field evolution in mammals: the predation risk, nocturnal restriction, and arboreal-depth perception hypotheses. Among mammals, binocular vision is most strongly associated with the primates. The ‘nocturnal visual predation hypothesis’ incorporates the predation risk, arboreal-depth perception and nocturnal restriction hypotheses to explain visual field convergence among primates. We used phylogenetic generalized least squares regression to simultaneously test the various hypotheses that have been proposed to explain visual field evolution using a large sample of mammalian species (~329). We include data relevant to the hypotheses outlined above including body mass, habitat, activity period, social behavior, and trophic level. We fail to support the nocturnal restriction hypothesis. However, we find that habitat openness has interacted with body size and activity period during the evolution of orbital convergence in mammals. We show that a single hypothesis is insufficient to explain the evolution of morphological characters that are evolutionary mosaics, reflecting ecological and behavioral evolution among mammal clades.

SBN2-3  12:00 pm  Exploring the evolution of the auditory morphology of primates using in-situ soft-tissue visualization and geometric morphometrics . Stoessel A*, Max Planck Institute for Evolutionary Anthropology; Department of Human Evolution; David R, Max Planck Institute for Evolutionary Anthropology; Department of Human Evolution; Gunz P, Max Planck Institute for Evolutionary Anthropology; Department of Human Evolution; Ossmann S, Technische Universität Dresden; Klinik und Poliklinik für Hals-, Nasen- und Ohrenheilkunde; Hublin JJ, Max Planck Institute for Evolutionary Anthropology; Department of Human Evolution; Spoor F, Max Planck Institute for Evolutionary Anthropology; Department of Human Evolution & Department of Cell and Developmental Biology, University College London
Abstract: Extant primates show substantial diversity in their auditory morphology. Such variation is known be related to aspects of hearing and/or could also reflect morphological alterations of surrounding structures. Studying the ear region of fossil primates could thus shed light on their auditory capacities while potentially providing information on the evolution of the cranial base as well. Studying the ear region, however, remains methodologically challenging due to the complex three-dimensional morphology of its delicate structures hidden inside the temporal bone. Individual structures of the ear are thus commonly measured separately and hardly anything is known about their spatial relationships. Moreover, precisely inferring auditory function requires quantitative data about soft-tissues to be obtained, which remains to be done for primates. Here, we present an approach to quantitatively study the three-dimensional shape and functional relevant measures of the middle ear and cochlea, including essential soft-tissue structures. Applied to 27 primate species, this approach is based on contrast-enhanced in-situ visualization of micro-CT images and semilandmark-based geometric morphometrics (GM). Results of the GM analysis show in detail distinct differences in shape, size and spatial configuration of the ear region from tympanic membrane to cochlea across primates. Furthermore, functionally important measures like tympanic membrane area and cochlear duct volumes will be discussed. This approach expands the knowledge of the morphological diversity of the auditory region and provides a strong basis for reliably reconstructing its morphology and function in fossil primates. This research was funded by the Max Planck Society.

SBN2-4  12:15 pm  Some chameleons really do "hear it through the grapevine" Huskey S.H.*, Western Kentucky University; Anderson C.V., Brown University; Smith M.E., Western Kentucky University; Barnett K.E., New York State Department of Environmental Conservation
Abstract: Though less studied than airborne, acoustic communication, a number of animals communicate via substrate vibrations. For example, many bird species communicate with conspecifics via vibrations and elephants have been shown to communicate over long distances with vibrations through the ground. Further, it's believed that >90% of insects use some sort of vibration to communicate. One group that has been understudied in terms of vibratory communication is reptiles, likely because their vocalization abilities are often lacking and entire reptilian groups are deaf to airborne sounds (e.g. snakes). An exception is the veiled chameleon, Chamaeleo calyptratus, which can produce a low-frequency, buzzing sound emanating from the throat region, which we hypothesize to be produced by a specialized out-pocketing of the trachea known as the gular pouch. This sound results in a vibratory signal transmitted through a tree branch and is often used when the animal feels threatened or during courtship/mating. This is the first documented case of plant-borne, vibratory signaling in any reptile, and while anecdotally noted in other chameleon taxa as a threat response, this phenomenon has not been examined in detail in C. calyptratus or other chameleon species. Here, we compare gular pouch morphology among chameleon taxa and relate it to reported abilities to produce vibratory threat responses. We then hypothesize how these structures are used to generate seismic vibrations. Producing and detecting vibrations by chameleons may represent the earliest means of seismic communication among terrestrial vertebrates. As chameleons have neither the vocal cords or syrinx known to produce seismic vibrations in other terrestrial vertebrates, their vibrations must be produced in a completely novel way. These results therefore provide valuable insights into the evolution of key tracheal modifications and a novel communication strategy.

SBN2-5  12:30 pm  The origin of ultrasonic hearing in whales: new insights from morphometric studies of the inner ear. Churchill M*, New York Institute of Technology; Geisler JH, New York Institute of Technology; Martinez-Caceres M, National Museum of Natural History, Paris France
Abstract: Odontocetes (toothed whales) are rivaled only by bats in their ability to hear ultrasonic frequencies. However, the origin of ultrasonic hearing within whales is still unknown, and most studies on whale inner ear morphology have been qualitative, with few rigorous statistical analyses. To determine how and when ultrasonic hearing evolved, we performed PCA on 8 measurements of the cochlea taken from HR-CT scans of 25 whale and outgroup taxa. Several fossil odontocetes were sampled, including an early diverging xenorophid. Measurements analyzed included length of cochlea, length of secondary bony lamina, 2 measures of width of the basal turn, height of cochlea, maximum distance between turns, radius of the spiral ganglionic canal, and area of the fenestra cochlearis. Approximately 86% of the variation was explained by the first two components. PC 1 explained 56% of the variation and reflected overall variation in body size. PC 2 explained 29% of the variation and separated taxa into two discrete morphospaces: taxa that hear at ultrasonic frequencies, comprised of all odontocetes, and an infrasonic hearing morphospace, comprised of mysticetes and hippopotamids. Basilosaurids occupied an intermediate zone between both morphospaces. Xenorophid whales possess a high basal ratio and very long secondary bony lamina, both traits associated with ultrasonic hearing. However they possess a relatively small spiral ganglionic canal when compared to odontocetes, suggesting a lesser degree of acoustic signal processing ability than modern odontocetes. Using ancestral character state reconstructions generated by Mesquite 2.75, we determined that ultrasonic hearing evolved at the base of Odontoceti. Our study also demonstrated that initial enlargement of the spiral ganglionic canal and an increase in the length of the secondary bony lamina occurred within Archaeoceti, indicating that adaptation towards high frequency hearing preceded the evolution of echolocation in odontocetes.

SBN2-6  12:45 pm  Functional morphology of mysticete sound reception: constructing the first baleen whale audiogram using finite element modeling. Cranford T/W*, San Diego State University; Krysl P, University of California, San Diego; Potter C/W, Smithsonian Institution
Abstract: Vocalization frequencies in baleen whales (Mysticeti) overlap with low-frequency anthropogenic sound sources, but mysticete sound reception mechanisms are essentially unknown. Synthetic audiograms were generated for a fin whale by applying finite element modeling (FEM) tools to X-ray CT scans. We scanned the head of a small fin whale (Balaenoptera physalus) in an industrial CT scanner designed for solid-fuel rocket motors. Our custom FEM toolkit allowed us to visualize the interactions between sound and the anatomic geometry within the whale's head. Simulations reveal two mechanisms that excite each of the bony ear complexes (TPCs): (1) the skull-vibration enabled bone conduction mechanism and (2) a pressure mechanism transmitted through soft tissues. Bone conduction is the predominant mechanism that contributes to low-frequency sound sensitivity (Cranford and Krysl, 2015). Recent preliminary simulations suggest a sensory basis for directional hearing based on phase differences between waves that arrive at the TPCs through skull deformation. We have also succeeded in reconstructing an entire minke whale specimen (Balaenoptera acutorostrata) from CT scan data. These results have important implications for assessing mysticete exposure to levels of anthropogenic noise and for understanding various aspects of ecological morphology associated with baleen whale sound reception. [Cranford, T. W., and Krysl, P. (2015). "Fin Whale Sound Reception Mechanisms: Skull vibration enables low-frequency hearing," in PLoS ONE (Public Library of Science, San Francisco), p. e116222.] Funding for this project was provided by Dr. Michael Weise at the Office of Naval Research (N00014-12-1-0516).

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