A COMPARATIVE STUDY OF THE WEBERIAN APPARATUS IN THE GENERA DIONDA AND NOTROPIS (CYPRINIDAE) By Morgan Emery Sisk Bachelor of Science Murray State College Murray, Kentucky 1953 Submitted to the faculty of the Graduate School of the Oklahoma State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May, 1961 A COMPARATIVE STUDY OF THE WEBERIAN APPARATUS IN THE GENERA_DI9NDA AND NOTROPIS (CYPRINIDAE) cl.ARE.NGE J. eCOY JR. By Morgan Emery Sisk Bachelor of Science Murray State College Murray, Kentucky 1953 Submitted to the faculty of the Graduate School of the Oklahoma State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May, 1961 Name: Morgan Emery Sisk Date of Degree: May, 1961 Institution: Oklahoma State University Location: Stillwater, Oklahoma Title of Study: A COMPARATIVE STUDY OF THE WEBERIAN APPARATUS IN THE GENERA DIONDA AND NOTROPIS (CYPRINIDAE) Pages in Study: 50 Candidate for Degree of Master of Science Major Field: Zoology Scope and Method of Study: The bony elements of the Weberian apparatus from three species of Dionda and six species of Notropis were studied to compare and describe structural variations between the two genera. Specimens were procured from field collections and from the collec- tion of fishes at Oklahoma State University. A modification of the alizarin red—S method was utilized in staining the specimens. Dis- sections were made under a binocular microscope prior to or after clearing in glycerine and drawings were made in charcoal with the aid of a camera lucida. Findings and Conclusions: The Weberian apparatus in Notropis and Dionda incorporates the first four modified vertebrae none of which is fused to others. The apparatus of both genera is similar in many respects and highly variable in all species examined. The main differences noticed between the genera are: (1) a stouter and heavier pars sustentaculum in Notropis; (2) the presence of a spur— like process on the third neural pedicle in Notropis, absent in Dionda; (3) and usually a vertically elongate neural complex in Notropis, horizontally elongate and boat shaped in Dionda. The Weberian ossicles are of no taxonomic value since they are highly variable within species and often differ from left to right sides in single specimens. ADVISER'S APPROVAL A COMPARATIVE STUDY OF THE WEBER IAN APPARATUS IN THE GENERA DIONDA AND NOTROPIS (CYPRINIDAE) Thesis Approved: Thesis Adviser Dean of the Graduate School 11 ACKNOWLEDGMENTS The criticisms of Doctors G. A. Moore, B. P. Glass, and H. I. Featherly are greatfully acknowledged. Mr. A. P. Juhlin of the Okla- homa State University Library was most helpful in obtaining many valuable references, otherwise unavailable. Doctor Clark Hubbs of the University of Texas was most generous in providing specimens of Dionda diaboli Hubbs and Brown. Thanks are extended to Messrs. B. A. Rranson, M. R. Curd, C. J. McCoy and A. D. Niazi, fellow graduate students who assisted me in the field and in the laboratory. Doc-Or C. D. Riggs graciously provided the facilities of the University of Oklahoma Biological Station for summer research and assisted in collecting specimens. My wife Jane graciously assisted in the preparation of this work. 111 PREFACE It has been common practice in the past to classify fishes on the basis of external morphological structures and easily accessible parts of the internal anatomy. Today, it is essential that fish taxonomists examine more critically the finer details of hard and soft anatomy in order to better understand and more accurately establish true relation- ships between presently existing groups of fishes. A case in point is the superficial similarity of the genera Notropis and Dionda. The main criterion that has been used in separating these two genera is the long gut in Dionda and a short gut in Notropis. One could take the stand that Dionda is only a,Notropis,with a long gut. Such a stand has precedent in the genus Pimephales in which the gut length varies intra- specifically. Within the past decade one geographic population of Dionda was described as a full species of Notropis. Alvarez and Navarro (1953) described Notropis ipni from a southern race of Dionda rasconis (Jordan and Snyder), thus indicating the superficial resemblance of the two genera, according to Hubbs (1956). The present study involving all of the United States members of the genus Dionda - and six common species in the genus Notropis, was undertaken to investigate and describe in detail structural variations existing in the bony elements of the Weberian apparatus of these nine species of minnows. It was hoped that comparison of these osteological structurps in the two genera might help understand their relationship. i v TABLE OF CONTENTS Chapter Page I. INTRODUCTION ... 1 II. HISTORICAL REVIEW ... 3 III. MATERIALS AND METHODS ... 7 Collection of Fishes ... 7 Preparation of Specimens for Observation ... 8 Preparation of Illustrations ... 9 IV. OBSERVATIONS ............................................. 11 Pars Sustentaculum .................................. 11 Pars Auditum 17 V. DISCUSSION AND CONCLUSIONS ............................... 21 VI. SUMMARY .................................................. 35 VII. SUGGESTIONS FOR FURTHER STUDY ............................ 37 SELECTED BIBLIOGRAPHY ........................................... 38 APPENDIX ........................................................ 42 LIST OF TABLES Table Page I. Development of the Weberian Ossicles .... 6 LIST OF ILLUSTRATIONS Text Figure 1. General Plan of the Weberian Apparatus in the Ostariophy- sine Fishes Taken from Chranilov (1926) and Modified .... 1 Plate I. Dorsal, Ventral, Lateral, and Anterior Views of the Pars Sustentaculum of Notropis,cornutus and Dionda diaboli 43 Figure 1 - Lateral view of the pars sustentaculum in N. cdrnutus. Figure 2 - Dorsal view of the pars sustentaculum in N. cornutus. Figure 3 - Anterior view of the pars sustentaculum in N. cOrnutus. Figure 4 — Ventral view of the pars sustentaculum in cornUtus,._ Figure 5 - Lateral view of the pars suttentaculum in D. diaboli. Figure 6 - Dorsal view of the pars sustentaculum in D. diaboli. Figure 7 - Anterior view of the pars sustentaculum in D. diaboli. Figure 8 - Ventral view of the pars sustentaculum in D. diaboli. v i LIST OF ILLUSTRATIONS (Continued) Plate Page II. Lateral Views of the Neural Complex in Nine Species of Minnows ........................................... 45 Figure 9 - Neural complex of N. cornutus Figure 10 - Neural complex of N. zonatus Figure 11 - Neural complex of N. whipplei Figure 12 - Neural complex of N. lutrensis Figure 13 - Neural complex of N. venustus Figure 14 - Neural complex of N. percobramus Figure 15 - Neural complex of D. diaboli Figure 16 - Neural complex of D. episcopa Figure 17 - Neural complex of D. nubila III. Selected Views of the Weberian Ossicles of Six Species of Notropis ... 47 Figure 18 - Ossicles of N. cornutus Figure 19 - Ossicles of N. zonatus Figure 20 - Ossicles of N. percobromus Figure 21 - Ossicles of N. venustus Figure 22 - Ossicles of N. lutrensis Figure 23 - Ossicles of N. whipplei IV. Selected Views of the Weberian Ossicles of Three Species of Dionda .............................................. 49 Figure 24 - Ossicles of D. diaboli Figure 25 - Ossicles of D. episcopa Figure 26 - Ossicles Of D. nubila vii CHAPTER I INTRODUCTION According to Krumholz (1943)1 E. H. Weber in 1820 described a chain of bones connecting the air-bladder to the inner ear in the old world catfish, Silurus cilanis Linnaeus. The group of fishes possessing this remarkable structure was named Ostariophysaea by Sagemehl (1891). Jordan (1929) defined the series Ostariophysi as "fishes with the an- terior vertebrae modified to connect with the air-bladder and inclos- ing an organ of hearing." The general plan of the Weberian apparatus in the ostariophysine fishes (Text Figure 1) consists of the first four or five anterior vertebrae modified to form the pars sustentaculum or supporting OS SUSPENSORIUM INTER CALARIUM SCAPHIUMi SINUS IMPARIS Allip,CLAUSTRUM SINUS AIR ENDOLYMPHATICUS \41ca BLADDER DUCTUS ATRIUM ENDOLYMPHATICUS SINUS IMPARIS OSSICUL AR LIGAMENT TRIPUS I-17=MODIFIED VERTEBRAE Text Figure 1. 1 2 mechanism of the apparatus. Associated with the pars sustentaculum are three or four ossicles, small bones connecting the anterior chamber of the air bladder to the inner ear, which are collectively referred to as the pars auditum. These ossicles are thought to be derived from the modified vertebrae. Between the left and right inner ears there is a connecting duct, the ductus endolymphaticus, containing endolymph. Projecting posteriorly from this duct is a median diverticulum, the sinus endolymphaticus. Enclosing the sinus endolymphaticus, but not openly communicating with the sinus or ductus endolymphaticus, is a median tube containing perilymph, the sinus imparis. This sinus divides posteriorly to form a pair of cavities, the atria sinus imparis, whose posterior medial and lateral walls are formed by one or two of the anterior ossicles. The function of the Weberian apparatus has never been definitely determined. Several theories have been proposed relative to its physio- logical function: registering changes in atmospheric pressure, serving as an aid to hearing, and functioning as a hydrostatic organ. Recent experiments by Wunder (1936), von Frisch (1938), Poggendorf (1952), and others indicate the apparatus may serve any one or more of the proposed functions.