Amphibian Cytogenetics and Evolution

456 Pages·1991·15.13 MB·English

by  David M. Green and Stanley K. Sessions (Eds.)

AMPHIBIAN
CYTOGENETICS
AND
EVOLUTION
EDITED BY
David M- Green
Redpath Museum
McGill University
Montreal, Quebec, Canada
Stanley K- Sessions
Department of Biology
Hartwick College
Oneonta, New York
ACADEMIC PRESS, INC.
Harcourt Brace Jovanovich, Publishers
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London Sydney Tokyo Toronto
Front cover illustrations by Michael De Braga.
Photomicrograph of chromosomes from the frog
Leiopelma hochstetteri, by David M. Green.
This book is printed on acid-free paper. 0
Copyright © 1991 by ACADEMIC PRESS, INC.
All Rights Reserved.
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Academic Press, Inc.
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United Kingdom Edition published by
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Library of Congress Cataloging-in-Publication Data
Amphibian cytogenetics and evolution / edited by David M. Green and
Stanley K. Sessions.
p. cm.
Includes index.
ISBN 0-12-297880-3
1. Amphibians-Cytogenetics. 2. Amphibians-Evolution.
I. Green, David Martin. II. Sessions, Stanley Keith.
QL668.5.A56 1991
597.6O415--dc20 91-2752
CIP
PRINTED IN THE UNITED STATES OF AMERICA
91 92 93 94 9 8 7 6 5 4 3 2 1
Contributors
Numbers in parentheses indicate the pages on which the author's contributions begin.
Karen Anderson (299), Department of Biology, Hofstra University,
Hempstead, New York 11550
James P. Bogart (233), Department of Zoology, University of Guelph,
Guelph, Ontario NIG 2W1, Canada
Harold G. Callan (217), Gatty Marine Laboratory, University of
St. Andrews, Fife KY16 8LB, Scotland
Jose Roberto Alegria Coto (157), Departamento de Biologia, Facultad de
Ciencias y Humanidades, Universidad de El Salvador, San Salvador,
El Salvador
J.T. Epplen (393), Max Planck Institute for Psychiatry, Martinsried,
Germany
David M. Green (1, 333,431), Redpath Museum, McGill University,
Montreal, Quebec H3A 2K6, Canada
T. Haaf (393), Department of Human Genetics, University of Würzburg,
Koellikerstr. 2, D-8700 Würzburg, Germany
David M. Hillis (7), Department of Zoology, University of Texas, Austin,
Texas 78712
Chikako Ikebe (67), Department of Biology, Toho University, Funabashi,
Chiba 274, Japan
K. Kausch (393), Department of Human Genetics, University of Würzburg,
Koellikerstr. 2, D-8700 Würzburg, Germany
James Kezer (89), Department of Biology, University of Oregon, Eugene,
Oregon 97403
xi
xii Contributors
Max King (359), Museum of Arts and Sciences of the Northern Territory,
Darwin, Northern Territory 0801, Australia
Sei-ichi Kohno (67), Department of Biology, Toho University, Funabashi,
Chiba 274, Japan
Masaki Kuro-o (67), Department of Biology, Toho University, Funabashi,
Chiba 274, Japan
Pedro E. Leon (157), Centro de Investigaciones en Biologia Celular y
Molecular (CIBCM) and Escuela de Medicina, Universidad de Costa
Rica, Ciudad Universitaria Rodrigo Facio, San Jose, Costa Rica
Herbert C. Macgregor (175), Department of Zoology, University of
Leicester, Leicester LEI 7RH, England
Giorgio Mancino (197), Dipartimento di Fisiologia e Biochimica, Laboratori
di Biologia Cellulare e dello Sviluppo, via G. Carducci, 13, La Fontina,
1-56010 Ghezzano, Pisa, Italy
I. Nanda (393), Department of Human Genetics, University of Würzburg,
Koellikerstr. 2, D-8700 Würzburg, Germany
Irma Nardi (131), Dipartimento di Fisiologia e Biochimica, Laboratori di
Biologia Cellulare e dello Sviluppo, via G. Carducci 13, La Fontina,
1-56010 Ghezzano, Hsa, Italy
Ronald A. Nussbaum (33), Museum of Zoology and Department of Biology,
University of Michigan, Ann Arbor, Michigan 48109
M. Schmid (393), Department of Human Genetics, University of Würzburg,
Koellikerstr. 2, D-8700 Würzburg, Germany
Stanley K. Sessions (1, 89,431), Department of Biology, Hartwick College,
Oneonta, New York 13820
C. Steinlein (393), Department of Human Genetics, University of Würzburg,
Koellikerstr. 2, D-8700 Würzburg, Germany
Janina Tymowska (259), Station de Zoologie Exporimentale, Universite de
Gendve, 154 route de Malagnou, CH-1224, Chene-Bougeries/Geneva,
Switzerland
Preface
Cytogenetics, the study of chromosomes, is undergoing a modern-day
renaissance. Employing methods pioneered in molecular biology, molecu-
lar cytogenetics promises to overcome previous limitations of classical
chromosome study based on stained chromosomes. Comparative, evolu-
tionary cytogenetics is reaping the benefit. This book, "Amphibian Cy-
togenetics and Evolution," appears at a time when molecular cytogenetics
is poised to make significant impact on evolutionary studies, enabling
problems of chromosomal structure and change to be critically addressed.
The early stages of any field are full of excitement; for a time, any new
discovery is momentous. This is as true, for instance, of the early years of
scanning electron microscopy in the 1960s and isozyme electrophoresis in
the 1970s as for molecular biology in the 1980s. The early years of modern
cytogenetics in the 1950s were similarly full of excitement as "squash and
splash" methods for making preparations were discovered and chromo-
somes could be seen in their glory. Chromosome-banding methods held
even more promise of ever more precise characterization of chromo-
somes.
However, as in many fields that promise answers for unsolved ques-
tions, the early flush of enthusiasm for a new enterprise fades as the
limitations of techniques inevitably become apparent and newer methods
appear. So it was for the early promise of cytogenetics for evolutionary
biology, as for isozymes and, even now, for restriction fragment-length
polymorphisms in molecular studies. All of these methods still have their
uses, but their glamor as routes to knowledge has dimmed. Yet cy-
togenetics, the direct examination of genome structure, is complementary
to the examination of genome organization at the molecular level and,
thus, has been rejuvenated by new methods, including use of monoclonal
antibodies, DNA sequencing, and in situ hybridization, the use of which
are illustrated by many of the contributions in this book.
xiii
xlv Preface
Yet, as much as it is about cytogenetics, this book is also about
amphibians. Chromosome evolution in amphibians has been far from
static. Among anurans, there is great variation in chromosome number,
from In = 14 in the African frog genus Arthroleptis, to In = 62 in the
Chinese frog Rana phrynoides, and 8n = 104 in the South American
polyploid frog Ceratophrys ornata. Within the huge frog genus Eleuthero-
dactylus, with over 450 species, diploid chromosome numbers range from
18 to 36. In salamanders, diploid chromosomes number range from 22 in
North American salamandrids to 78 in the hynobiid Onychodactylus ja-
ponicus. Nor is polyploidy unusual in amphibians. Naturally occurring
triploid, tetraploid, and even pentaploid salamanders are known in the
Ambystoma jeffersonianum complex, and triploids are common in the
self-perpetuating hybrid frogs known as "Rana esculenta." The North
American grey treefrogs Hyla chrysoscelis and Hyla versicolor are sibling
species, diploid and tetraploid, respectively, and polyploidy has character-
ized the speciation of frogs in the genus Xenopus. All species in the
salamander family Sirenidae appear to be polyploid, with variable chromo-
some numbers and morphologies. Supernumerary chromosomes are
found in many species of both salamanders and frogs. Banding studies
reveal extensive diversity in the amounts, kinds, and distributions of
heterochromatin, nucleolus organizer regions, and other chromosome
structures. Amphibians exhibit all stages of sex chromosome differentia-
tion, from complete homomorphism to extreme heteromorphism. This is
readily seen within the single salamander genus Necturus and especially
within the bolitoglossine plethodontid salamanders. Both male (XY/XX)
and female (ZZ/ZW) heterogametic systems are present among am-
phibians. Genome sizes also vary enormously, from the small 5 pg of DNA
in the diploid nucleus of a Xenopus laevis to more than 165 pg of DNA in a
diploid nucleus of the salamander Necturus maculosus. Even within the
single family Plethodontidae, genome sizes range from 26 to > 152 pg per
diploid nucleus. Phenomena such as these are critically discussed by
contributors to this book.
Amphibians have great advantages as subjects for chromosome study.
With few exceptions, they do not have high chromosome numbers. Their
chromosomes are relatively large and easy to prepare. Lampbrush chro-
mosomes visible in meiotic oocyte nuclei of amphibians are ideal subjects
for in situ labeling and analysis of chromosome structure. Many amphibian
species, especially newts of the genus Triturus and frogs of the genus
Xenopus, are easily maintained in captivity and, thus, have been widely
used in genetic studies of many sorts. It is particularly valuable at this time
to bring together, in a single volume such as this, the latest information
about the evolutionary cytogenetics of these animals.
The utility and fascination of studying amphibian cytogenetics is well
Preface XV
known among its practitioners, yet for those in other fields studying differ-
ent groups of organisms, amphibians still have a reputation as extreme
karyotypic conservatives. In talking to colleagues at the annual meeting of
the American Society of Ichthyologists and Herpetologists (ASIH) in
1987, we thought that a symposium on the current state of affairs of
amphibian cytogenetics would be particularly timely, especially since Jim
Kezer, the teacher, colleague, and friend of amphibian cytogeneticists
everywhere, was approaching his eightieth birthday. The symposium in
honor of Jim Kezer, who was in attendance, was entitled "Amphibian
Cytogenetics and Evolution" and hosted by the ASIH. It was organized by
the editors of this book with support from the Bowerman Foundation of
Oregon and held in San Francisco in 1989.
Although inspired by the 1989 symposium, this book is not a sym-
posium volume. Several chapters are not based on presentations given at
the symposium, and some symposium papers are not included here. Gath-
ered together for the first time are chapters concerning the cytogenetics of
all three orders in the class Amphibia: caecilians (Gymnophiona), sala-
manders (Caudata), and frogs (Anura). Each chapter deals with a specific
topic of present interest. Some chapters deal primarily with chromosomal
variation within particular groups, caecilians or bolitoglossine salaman-
ders for example, whereas others examine more general cytogenetic phe-
nomena, such as heterochromatin evolution, supernumerary chromo-
somes, or sex chromosomes, across all groups of Amphibia. The result is
an up-to-date and comphrehensive survey of the cytogenetics of a major
class of animals with contributions by the leaders in the field around the
world. "Amphibian Cytogenetics and Evolution" will be of interest to
classical and molecular cytogeneticists, evolutionary biologists, herpetol-
ogists, and anyone using amphibians in genetic research.
All the contributions in this book were reviewed by third parties. We
are grateful to J. J. Bull, C. J. Cole, J. G. Gall, D. A. Good, B. Hamkalo,
R. F. Inger, R. N. Jones, A. Larson, L. R. Maxson, C. Moritz, M.
Romano, R. D. Sage, S. W. Sherwood, D. B. Wake, and M. Wake for their
time and helpful comments. We also thank our editor at Academic Press,
Phyllis B. Moses, for her efforts on behalf of this project. Many of the tasks
associated with the preparation of the manuscripts for publication were
assisted by Delise Alison, Jeanne Armstrong, Hinrich Kaiser, David A.
Good, Christele de Souich, and Tim Sharbel. We also thank the American
Association of Ichthyologists and Herpetologists for their sponsorship of
the 1989 symposium and Jay Bowerman and the Bowerman Foundation
for much needed financial help in bringing the participants together. Fi-
nally, we thank Jim Kezer, who continues to inspire us all.
David M. Green and Stanley K. Sessions
CHAPTER 1
James Kezer: A Pioneer in
Amphibian Cytogenetics
Stanley K* Sessions David M* Green
Department of Biology Redpath Museum
Hartwick College McGill University
Oneonta, New York Montreal, Quebec, Canada
This book is dedicated to Dr. James Kezer, Professor Emeritus at the
University of Oregon in Eugene, Oregon. Jim (Fig .1) is known by friends
and colleagues throughout the world not only as a pioneer in the field of
amphibian cytogenetics but also because of the positive influence he has
on everyone he encounters. It is impossible for anyone who has met him to
forget him. The first encounter that one of us (SKS) had with Jim was in
Edward Novitski's evolution course at the University of Oregon, where
Jim gave a guest lecture one day on the chromosomes and evolution of
plethodontid salamanders. Sessions was an undergraduate at the time and
he had never before (or since) witnessed a teacher so excited about any
subject. The experience had a heavy impact and in fact has influenced the
course of Sessions' professional career.
Jim's research interest in salamander cytogenetics has its roots in the
1930s, when Jim was working as a high school teacher in New Jersey.
During the summer of 1932, he attended Cornell University where he took
courses from E. L. Palmer in science education, A. A. Allen in ornithol-
ogy, and A. H. Wright in herpetology and natural history. It was during
this first summer at Cornell, in Wright's natural history course, that Jim
had his first encounter with plethodontid salamanders. During a field trip
into Cascadilla Gorge along the edge of the Cornell Campus, Wright
showed to his students specimens of the common redback salamander,
Plethodon einereus. This experience so inspired Jim that he incorporated
natural history and herpetology into his high school science courses,
including field trips where he and his students carried out systematic
surveys of local vertebrates, including especially the salamanders.
To pursue his interests in salamanders at deeper levels, Jim entered a
Ph.D. program at Cornell in 1938, where a cytology course alerted him to
the possibility of using chromosome variation to study evolutionary rela-
tionships among plethodontid salamanders. A survey of the literature
AMPHIBIAN CYTOGENETICS AND EVOLUTION 1
Copyrisht © 1991 by Academic Press, Inc.
All Rights of Reproduction in any Form Reserved.
2 Stanley K. Sessions and David M. Green
Figure 1. James Kezer in 1967 at the University of Oregon.
showed that almost nothing was known about this topic at the time and so
he made it the subject of his Ph.D. research.
Jim's graduate work was interrupted in 1942 by World War II and a
4-year stint in the army, during which time he advanced from buck private
to second lieutenant and was put in charge of bacteriology and serology for
the 55th General Hospital in England and France. After leaving the army in
1946 with the rank of captain, Jim returned to graduate school at Cornell to
continue his research on salamander cytogenetics.
Jim's thesis work was initially extremely difficult and frustrating. The
standard cytogenetic techniques of the time involved analysis of paraffin
sections, which made it almost impossible to determine chromosome num-
bers and morphology with any accuracy. A major breakthrough occurred
when Jim began to apply squashing techniques to his salamander material
(Fig. 2). Although this method had been commonly used by plant cy-
togeneticists, this was the first time that it had been used for animal cells.
1. James Kezer 3
The technique produced exquisite, well-spread chromosome preparations
in which chromosome number and morphology were clearly visible. Jim
used this method long before human cytogeneticists began using similar
methods to accurately determine the number of chromosomes in a human
karyotype. With this technical success, Jim immediately launched a com-
parative study of the karyotypes of all plethodontid salamanders.
In one of life's strange ironies, after years of frustration and finally a
breakthrough providing an effective method to examine chromosome vari-
ation in detail, Jim's first major discovery was that all the plethodontid
species he examined had nearly identical karyotypes with 14 bi-armed
chromosomes! This discovery had two effects on his research. First, Jim
decided to look for chromosomal variation at higher levels of resolution
and began detailed studies of the meiotic behavior of salamander chromo-
somes, whose large size (Fig. 3) turned out to be an advantage for visualiz-
ing the various meiotic stages. Second, Jim decided to learn how to pre-
pare and investigate the lampbrush chromosomes found in amphibian
oocytes. This led to visits to H. G. (Mick) Callan's laboratory in St.
Andrews, Scotland, where Jim established working relationships with Joe
Figure 2. How to make a "chromosome squash" preparation.