Hybrid Zones and the Evolutionary Process RICHARD G HARRISON Hybrid Zones and the Evolutionary Process Copyrighted material Hybrid Zones and the Evolutionary Process EDITED BY RICHARD C.HARRISON Cornell University Ithaca, New York N e w York Oxford OXFORD UNIVERSITY PRESS 1993 O x f o r d U n i v e r s i t v Press Oxford New York Toronto Delhi Bombay Calcutta Madras Karachi Kuala Lumpur Singapore l l o n g Kon¡i Tokyo Nairobi l>ar es Salaam Cape Town Melbourne Auckland Madrid and associated companies in Berlin Ibadan C o p y r i g h t ® 1993 b y O x f o r d U n i v e r s i t y Press I n c Published by Oxford University Press Inc.» 200 Madison Avenue, New York, New York lOOlf* Oxford isa registered trademark of Oxford University Pre» All rights reserved* N o part o f this publication may be reproduced* stored in a retrieval system^ or transmitted, in any Ibrm or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission o f Oxford University Press Library of Congress Caialoging-in-PuWiculkm Data Hybrid zones and the evolutionary process /edited by Richard G Harmon p cm Includes bibliographical references and index ISBN0-19-MJÓ9I7-X Hybrid zones—Congresses Hybridization—Congresses Evolution (Biology)—Congresses I Harrison, Richard a {Richard Gerald) 1945- QH42I.HB3 1993 5?5-dc20 92-28327 987654321 Printed in the United Slates o f America on acid-free paper Preface Hybrid zones (imergrade zones) have figured prominently in ihe evolutionary biology literature for more than a century The decades between 1970 and 1990 witnessed a maturation of hybrid zone theory and a veritable explosion o f empirical data derived from long-term, multidisciplinar studies o f many hybrid zones This volume rcprescntsan attempt to summarize the current state o f knowledge In so doing, it hopefully provides a stimulus for future research Most o f the chapters included in the book have evolved from presentations given as pan o f an invited symposium ("Hybrid Zones and the Evolutionary Process") at the Fourth International Congress of Systematic and Evolutionary Biology (ICSEB) in College Park Maryland, held in July 1990 I h e organizers of the Congress not onlyinvited me to organize a symposium on hybrid zones but provided logistic and finan­ cial support, both of which were critical to the success o f the full-day symposium and the half-day workshop that followed O f the participants in the symposium, all but one were able to contribute to this book In addition I solicited chapters from evolutionary biologists who were not part of the original symposium These contributions focus on problems and groups of organisms not well represented in the presentations at ICSEB They make the book a more representative sample o f the hybrid zone literature Each of the chapters has been carefully reviewed and (in most cases) extensively revised* f very much appreciate the willingness o f colleagues to provide careful reviews o f these chapters I am particularly indebted to the contributors, who have been remarkably patient during the prolonged gestation period o f this book I have been a demanding editor and they have been wonderfully responsive to my requests The book is divided into two major parts Part I includes four chapters that exam­ ine some o f the major conceptual and practical issues associated with the study of hybrid zones Chapter I provides a historical perspective on hybridization and hybrid zones and an overview o f major issues; and Chapters 2-4 examine genetic analyses of hybrid zones, the evidence for reinforcement, and the nature and consequences of inlrogression in plants Part II includes a series of case studies These studies represent summaries o f long-term research programs that have focused on single hybrid zones or on clusters of hybrid zones within particular groups o f organisms I f this book were a complete compendium of hybrid zone research, many other well-studied hybrid zones would certainly have been included I apologize to those hybrid zone researchers whoseworkisnot represented here and hope that they will understand that it was time Copyrighted material vi PREFACE and space constraints (not the quality of their research) that led me to limit the dimen­ sions of this book Finally, I wish to express my appreciation to many colleagues and students (past and present) who have shared my enthusiasm for studying hybrid zones, bolstering my confidence that a program of research on hybrid zones is a worthwhile endeavor, am also grateful to the National Science Foundation Systematic Biology Program, which has generously funded my own hybrid /one research over the past 15 years* Ithaca N.Y July 1992 R.G.H Copyrighted material Contents Contributors Part I ix Hybrid Zone Pattern and Process 1 Hybrids and Hybrid Zones: Historical Perspective RirhardG Harrison Genetic Analysis of Hybrid Zones Nirhola* M Barton and KaiherineS Gale 13 Reinforcement: Origin, Dynamics, and Fate of an Evolutionary Hypothesis 46 Danirl I Howard IntroRression and Its Consequences in Plants Lorcn H Ricscbcrg and Jonathan F Wcndcl P a r l II Case Studies of Hybrid Zones 70 111 Natural Hybridization in Louisiana Irises: Genetic Variation and Ecological Determinants Michad L, Arnold and Bobby D Bennett IS After the Ice: Parallelus Meets Erythropus in the Pyrenees Godfrey M Htruitt 140 \ G e n o m i c a n d Environmental Determinants of a Narrow Hybrid Zone: Cause or Coincidence U£ David D, Shaw Adam D Marchan!, Nelida Comreras, Michael L Arnold» Fran Groctcrs, and BeriC Knhlmann 8, Nature of Selection in the Northern Flicker Hybrid Zone and Its Implications for Speciation Theory 196 William S Moore and JeffT Price Speciation, Raciation and Color Pattern Evolution in Heliconius Butterflies: Evidence from Hybrid Zones 226 ■lamre M a l W 10, Analysis of Hybrid Zones with Bombing Jacek M, S/ynmra 261 Copyrighted material viü CONTENTS 11 Hybridization and Hybrid Zones in Pocket Gophers (Rodentia Geomyidae) 290 JamcsJ Pattnn 12 Chromosomal Hybrid Zones in Eutherian Mammals Jeremy B Scarlc 309 Copyrighted material Contributors Michael I „ Arnold Department of Genetics University of Georgia Athens Georgia 30602 Nicholas H Barton Institute of Cell, Animal and Population Biology Division of Biological Sciences University of Edinburgh Edinburgh EH9 3JT United Kingdom Bobby P Bennett Department of Biological Sciences P o Rnv * w Arkansas State University State University Arkansas 72467 NftliHa