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Session Schedule & Abstracts

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Saturday 2nd July, 2016

Symposium: Life Underground: Morphological Consequences of Fossoriality 1

Room: Salon F   11:30 am–1:00 pm

Moderator(s): C. A. Hipsley, E. Sherratt, & H. C. Maddin
FOS2-1  11:30 am  Ontogeny of a burrowing morphology - examples from anurans and caecilians (Lissamphibia: Anura and Gymnophiona). Mueller H*, Department of Comparative Zoology, Jena University
Abstract: In general, burrowing taxa show a broad range of different morphological specialisations that are usually absent or less elaborate in their surface-dwelling relatives. In amphibians these include a more stout body shape, modified limbs, more heavily ossified skeletal elements and keratinized tubercles. Most amphibians have a biphasic life cycle in which an aquatic larval stage and a more terrestrial adult stage are punctuated by a profound metamorphosis. Larval and adult morphologies are each adapted to very different environments and feeding strategies and the feeding apparatus becomes temporarily non-functional during metamorphosis. Most amphibians metamorphose rapidly to quickly transition this maladapted phase and juvenile skeletons, though functional, are usually only incompletely ossified. In addition to the constraints imposed by metamorphosis, emerging metamorphs of burrowing amphibians need to commence a burring lifestyle, which in turn necessitates a more rigid and more heavily ossified skull than usually found in amphibian metamorphs. I present data on the development of burrowing and fossorial frogs (Hemisus, Breviceps) and caecilians (e.g. Ichthyophis, Gegeneophis, Boulengerula) that highlight some of the challenges faced by burrowing amphibians and how these have been addressed.

FOS2-2  11:45 am  Morphological diversity of the pectoral girdle and anterior body axis in Amphisbaenia. Mueller J*, Museum fuer Naturkunde Berlin; Camey S, Museum fuer Naturkunde Berlin; Hipsley CA, Museum fuer Naturkunde Berlin
Abstract: The fossorial Amphisbaenia, or worm lizards, are characterized by extensive body elongation, limb loss, and the reduction of the appendicular skeleton. Despite the superficially uniform appearance there is a high degree of variation in the amphisbaenian postcranium, but so far there have been only a few attempts to assess this variability in a both taxonomically and phylogenetically comprehensive framework. Here we present the first results of our analysis of the anterior body axis and the pectoral girdle, which is part of an ongoing, extensive assessment of amphisbaenian osteology using micro-computed tomography. In contrast to previous claims, shoulder girdle elements or remnants thereof are not only found in blanids, bipedids and trogonophids, but also in several genera of amphisbaenids. Also, we found clavicles, scapulocoracoids and parts of the sternum in the enigmatic genus Cadea, which was formerly considered to be amphisbaenid but now is thought to be closely related to blanids, the latter showing a similar number of elements. Our data suggest that the reduction of pectoral elements occurred many times independently, and also within the different major clades. In addition, we recorded substantial variation in the morphology of the cervical and anterior thoracic vertebrae, and found that this variation is, at least in part, phylogenetically informative, fitting recently proposed hypotheses of relationships. Especially some African amphisbaenids show a highly derived cervical morphology, which seems to be related to the evolution of shovel-headed skull shapes and associated digging styles. The variable position of the pectoral elements relative to the cervical region, which can be especially seen in bipedids and some trogonophids, suggests developmental plasticity and potential frame shifts during amphisbaenian evolution.

FOS2-3  12:00 pm  Evolution of cranial features associated with the "freight-train" burrowing of uropeltid snakes. Olori J.C.*, SUNY Oswego; Brown L., SUNY Oswego
Abstract: The head-first burrowing style employed by uropeltid snakes is a unique form of internal concertina locomotion. Uropeltids have a hyper-mobile cranio-vertebral joint and form tight curves with their anterior vertebrae, using those to push off tunnel walls and drive the skull directly forward through substrate. This burrowing style is expected to generate strong forces at the tip of the premaxilla, with stress propagated longitudinally along the nasals, frontals, parietals, and fused braincase. However, this "freight train" digging was characterized through study of more recently derived uropeltids, which exhibit a higher degree of fusion and modification of skull elements. Considerably less is known about more basally positioned taxa, which were described primarily from dried skeletons. In order to access anatomical regions normally obscured in traditional skeletal preparation, alcohol preserved skulls of Melanophidium punctatum and Teretrurus sanguineus were subjected to micro-CT and individual bones were digitally disarticulated and described. Compared to more crown-ward taxa such as Uropeltis, M. punctatum and T. sanguineus present not only a larger number of separate skull elements, but a greater amount of sutural space between bones. In M. punctatum, few of the non-braincase elements make direct contact and some are widely separated by thick regions of soft tissue. Given the variation in bone relationships across uropeltids, basally positioned species may exhibit more cranial kinesis than has been presumed for the clade, and may lack the highly specialized version of "freight train" burrowing seen in crown-ward taxa. Of broader importance, the anatomical differences apparent between dried and alcohol preserved skulls may have consequences for the validity of biomechanical studies, such as Finite Element Analysis, based on scans of traditional skeletal preparations, or lacking sutural data.

FOS2-4  12:15 pm  Blind, naked, and feeling no pain: sensory neurobiology of the naked mole-rat (Mammalia: Bathyergidae). Park TJ, University of Illinois at Chicago; Browe BM*, University of Illinois at Chicago
Abstract: Around the world and across taxa, subterranean mammals show remarkable convergent evolution in morphology (e.g. reduced external ears, shortened limbs and tails). This is true of sensory systems as well. Subterraneans have lost object vision and high frequency hearing. The naked mole-rat (Heterocephalus glaber) displays these typical subterranean features, but also has unusual characteristics even among other subterranean mammals and even other mole-rat species. Naked mole-rats are cold-blooded, completely furless, very long-lived (> 30 years) and eusocial (like bees). They also live in large colonies, which is very unusual for subterraneans. We are studying yet other unusual characteristics. First, the naked mole-rat is the only mammal whose pheromone-detecting vomeronasal organ (VNO) shows no postnatal growth, and sexual suppression is not mediated by urinary signals as in other rodents. Second, the nerve network for processing pain from noxious chemicals (e.g. acid and capsaicin) is reduced and lacks the neurotransmitter, Substance P, that usually signals pain. Naked mole-rats are the only mammals that feel no pain from these substances. Third, brain tissue from naked mole-rats is extremely tolerant to oxygen deprivation, and can recover from up to 30 minutes of anoxia. These features may be a result of this species' "extreme subterranean lifestyle" that combines living underground and living in large colonies. Many respiring animals cramped together in unventilated burrows raises CO2 levels enough to cause acidosis and chemical pain, and depletes O2 concentrations low enough to kill other mammals. Coincidentally, Substance P (lacking in the naked mole-rat) also mediates the VNO's vascular pump. The naked mole-rat may be an extreme model of adaptation to subterranean life and provides insights into the complex interplay of evolutionary adaptation to the constraints of subterranean living.

FOS2-5  12:30 pm  Climate change impacts on the fossorial herpetofauna of the globe: integrating models across paleo, contemporary and future timeframes. Sinervo Barry*, UC Santa Cruz; Miles Donald, Ohio University
Abstract: Models predict anthropogenic climate change will generate extinctions in the next century. Current models assume that extinctions will be triggered by severe demographic challenges faced by populations experiencing warming or drying but most models are correlative at best. Here, we develop new ecophysiological species distribution models, predicated on thermal physiology, that can be used to predict extinctions of ectotherms due to climate change. We apply these models to predict extinctions of fossorial reptile taxa in present and future timeframes and compare extinctions in these taxa that are thermoconformers to above ground taxa that are either heliotherms or thermoconformers. We also calibrate extinction models against reconstructed paleodistributions, back to the Eocene, the warmest period in the last 65 million years. Models predict the paleobiogeography of both above ground and fossorial taxa as validated by fossil inferences and inferences derived from phylogenetic patterns as related to the biogeographic origins of taxa at global scales. Fossorial reptile taxa appear to be buffered from the impacts of climate change compared to above ground taxa. This research was funded by an Emerging Frontiers Grant from NSF (EF-1241848).

FOS2-6  12:45 pm  Comparative morphology of the shoulder muscles of Amphisbaenia (Reptilia, Squamata) using iodine-staining and computed tomography. Westphal N.*, Museum fuer Naturkunde, Berlin; Mueller J., Museum fuer Naturkunde, Berlin; Mahlow K., Museum fuer Naturkunde, Berlin
Abstract: The bony shoulder girdle of worm lizards, or Amphisbaenia, shows variable degrees of reduction across different clades. Bony and cartilaginous shoulder girdle elements are reduced in all taxa, with Bipedidae showing the least degree of reduction and many Amphisbaenidae and Rhineuridae having completely lost the pectoral girdle. In contrast to the bony elements, little is known about the pectoral muscles of Amphisbaenia, and it remains unclear if they experienced reductions similar to those of the ossified skeleton. Here we present a comparative analysis of the pectoral muscles of Rhineura floridana, Blanus cinereus, Bipes biporus, Trogonophis wiegmanni, and Cynisca leucura, which are representatives of all the major clades of Amphisbaenia. Specimens were iodine-stained using 20% aqueous IKI solution and scanned using micro-computed tomography. In total, 17 pectoral muscles, nine superficial and eight deeper muscles, could be identified for all taxa except Rhineura, in which muscles were strongly reduced. The morphology of the muscles largely compares to that of the lacertid lizard Meroles, which was used as outgroup, whereas adjacent muscles variably tend to fuse in the different species. In Trogonophis and Cynisca, four superficial muscles, the M. latissimus dorsi, the M. episternocleidomastoideus, the M. trapezius, and the M. pectoralis together form an extensive ring structure, which might be considered a synapomorphy of trogonophids and amphisbaenids. The arrangement of the pectoral muscles remains constant in amphisbaenians except Rhineura, despite variable degrees of bone reduction. Instead of attaching to bony or cartilaginous elements, muscles arise from or insert into other muscles, skin or cartilage near the ancestral area of bony attachment. Our study presents the first detailed analysis of amphisbaenian pectoral myology, and provides compelling evidence that bone reduction is not necessarily accompanied by similar changes in muscle anatomy.

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