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Session Schedule & Abstracts




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Thursday 30th June, 2016

PHA3
Symposium : The vertebrate pharynx: crossroads in evolution and development 3

Room: Salon H   2:30 pm–4:00 pm

Moderator(s): A. Huysseune & A. Tucker
PHA3-1  2:30 pm  What happened to the gills during the fish-to-tetrapod transition? Schoch RR*, Staatliches Museum fuer Naturkunde Stuttgart   rainer.schoch@smns-bw.de
Abstract: The internal gills of bony fishes were long thought to have been lost before tetrapods evolved, with lungs and the skin forming the main respiratory organs in terrestrial vertebrates. Fossil evidence and phylogenetic bracketing instead reveal that the story was more multi-facetted. In fact, many early tetrapods were aquatic throughout life, and some of these retained internal gills homolgous with those of their sarcopterygian ancestors. In the stem-group of modern amphibians, these gills were retained in some aquatic clades, whereas in stem-amniotes, they were lost. A novel feature that evolved only in tetrapods are external gills of larval forms, absent in the immediate ancestors of tetrapods, but which are known to have existed in both stem-amphibians (temnospondyls) and stem-amniotes (seymouriamorphs). A survey of different breathing mechanisms in early tetrapods reveals complicated patterns of respiratory organs and mechanisms, highlighting that morphological disparity correlates with respiratory diversity.

PHA3-2  3:00 pm  Lungs to gas bladders: homology, novelty and transformation. McCune A.R.*, Cornell University; Cass A.N., North Carolina State University; Longo S.J., University of California, Davis; Riccio M.L., Cornell University; Funk E., Cornell University   arm2@cornell.edu
Abstract: An important evolutionary novelty among vertebrates is the gas bladder of ray-finned fishes, which develops dorsally as an outgrowth of the pharynx. Having a gas bladder characterizes nearly 30,000 species of the Actinopteri (all ray-finned fishes except polypterids). This air-filled organ may function in respiration, buoyancy, sound production, hearing or in some combination of these roles. Since the late 19th century, gas bladders have been regarded by most as homologous to lungs, although there continue to be those who disagree. Using data from micro- and nano- computed tomography (CT), we will illustrate the difference between lungs and gas bladders, review the evidence for and against homology, and present preliminary genetic data implicated in the transformation of lungs to gas bladders.

PHA3-3  3:30 pm  Diverse embryonic and evolutionary origins for the hypoxia-sensitive cells of the vertebrate respiratory reflex. Baker CVH*, University of Cambridge; Hockman D, University of Cambridge; Burns AJ, UCL Institute of Child Health; Mongera A, Max-Planck Institut für Entwicklungsbiologie; Fisher S, University of Pennsylvania; Unlu G, Vanderbilt University; Knapik EW, Vanderbilt University; Kelsh RN, University of Bath; Kaufman CK, Harvard Medical School; Mosimann C, Harvard Medical School; Zon LI, Harvard Medical School; Tucker AS, King's College London   cvhb1@cam.ac.uk
Abstract: Carotid body glomus cells respond to hypoxia by releasing neurotransmitters, triggering the respiratory reflex. It has been proposed that these neural crest-derived cells, which develop in association with the third pharyngeal arch artery, are homologous to the hypoxia-sensitive "neuroepithelial cells" (NECs) of fish gills. We test this hypothesis using genetic lineage-tracing and neural crest-deficient mutants in zebrafish, and physical fate-mapping in frog and lamprey. NECs in anamniote gill and orobranchial epithelia are not neural crest-derived, hence are most likely homologous to hypoxia-sensitive pulmonary neuroendocrine cells in lung airway epithelia, whose endodermal origin we confirm in mouse and chicken. We propose that carotid body glomus cells evolved instead from chromaffin cells associated with large pharyngeal arch blood vessels, which lineage-tracing in zebrafish shows are neural crest-derived.



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