Neural development in Onychophora (velvet worms) suggests a step-wise evolution of segmentation in the nervous system of Panarthropoda
Georg Mayer, Paul M Whitington
DEVELOPMENTAL BIOLOGY | ACADEMIC PRESS INC ELSEVIER SCIENCE | Published : 2009
A fundamental question in biology is how animal segmentation arose during evolution. One particular challenge is to clarify whether segmental ganglia of the nervous system evolved once, twice, or several times within the Bilateria. As close relatives of arthropods, Onychophora play an important role in this debate since their nervous system displays a mixture of both segmental and non-segmental features. We present evidence that the onychophoran "ventral organs," previously interpreted as segmental anlagen of the nervous system, do not contribute to nerve cord formation and therefore cannot be regarded as vestiges of segmental ganglia. The early axonal pathways in the central nervous system ..View full abstract
Awarded by German Research Foundation
G.M. thanks Paul Sunnucks for sharing his knowledge, organizing a collecting trip, and showing specimen-rich collecting sites at Tallaganda. We are thankful to Alvaro Herrera, Joakim Eriksson, Paul Sunnucks and Noel Tait for their assistance with collection of specimens. The staff of the Instituto Nacional cle Biodiversiclad (INBio, Heredia, Costa Rica), the National System of Conservation Areas (SINAC, MINAE, Costa Rica), the Department of Sustainability and Environment (Victoria, Australia), and State Forests NSW (New South Wales, Australia) are gratefully acknowledged for providing collecting and export permits. We thank Colin Anderson for allowing us to use his Vibratome and Shih Chieh Chang for sectioning sub-adult specimens of E. rowelli. We are grateful to Eli Mrkusich and Zalina Osman for their help in the laboratory, to Leonie M. Quinn for providing a cell death detection protocol and for encouraging discussions and comments on the manuscript, to Gerhard Scholtz for a helpful discussion, and to Andreas Schmidt-Rhaesa and Noel Tait for comments on the first draft. Three anonymous reviewers gave useful comments, which helped to improve the manuscript. This work was Supported by grants from the German Research Foundation (DFG, Ma 4147/1-1, 2-1) and the Department of Anatomy and Cell Biology (University of Melbourne) to G.M.