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Extinction Risk by Mutational Meltdown. Synergistic Effects Between Population Regulation and Genetic Drift

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Extinction Risk by Mutational Meltdown. Synergistic Effects Between Population Regulation and Genetic Drift Conservation Genetics Edited by V. Loeschcke J. Tomiuk S. K. Jain Birkhäuser Verlag Basel * Boston * Berlin Editors Dr. V. Loeschcke Dr. J. Tomiuk Institute of Ecology and Genetics Section of Clinical Genetics University of Aarhus University of Tübingen Ny Munkegade, Building 540 Wilhelmstr. 27 DK-8000 Aarhus C D-72074 Tübingen Denmark Germany Dr. S. K. Jain Department of Agronomy and Range Sciences University of California Davis, CA 95616 USA Library of Congress Cataloging-in-Publication Data Conservation genetics / edited by V. Loeschcke, J. Tomiuk, S. K. Jain. —(EXS; 68) Includes bibliographical references and index. ISBN 3-7643-2939-4—ISBN 0-8176-2939-4 1. Germplasm resources—Congresses. 2. Nature conservation—Congresses. 3. Popula• tion genetics—Congresses. I. Loeschcke, V. (Volker), 1950-. II. Tomiuk, J. (Jürgen) III. Jain, Subodh K., 1934 . IV. Series. QH75.A1C6655 1994 639.9'01'5751—dc20 Deutsche Bibliothek Cataloging-in-Publication Data Conservation genetics / ed. by V. Loeschcke. — Basel; Boston; Berlin: Birkhäuser, 1994 (EXS; 68) ISBN 3-7643-2939-4 (Basel. .) ISBN 0-8176-2939-4 (Boston) NE: Loeschcke, Volker; GT The publisher and editor can give no guarantee for the information on drug dosage and administration contained in this publication. The respective user must check its accuracy by Consulting other sources of reference in each individual case. The use of registered names, trademarks etc. in this publication, even if not identified as such, does not imply that they are exempt from the relevant protective laws and regulations or free for general use. This work is subject to Copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. For any kind of use permission of the Copyright owner must be obtained. © 1994 Birkhäuser Verlag, PO Box 133, CH-4010 Basel, Switzerland Printed on acid-free paper produced from chlorine-free pulp Cover illustration: Jon Fjeldsä Printed in Germany ISBN 3-7643-2939-4 ISBN 0-8176-2939-4 987654321 V Contents Preface ix Part I: Genetics and conservation biology V. Loeschcke, J. Tomiuk and S.K. Jain Introductory remarks: Genetics and conservation biology 3 G. Vida Global issues of genetic diversity 9 Part II: Genetic Variation and fitness Introductory remarks 23 O. Savolainen Genetic Variation and fitness: Conservation lessons from pines. 27 R.C. Vrijenhoek Genetic diversity and fitness in small populations 37 D. Couvet and J. Ronfort Mutation load depending on variance in reproductive success and mating System 55 W. Gabriel and R. Bürger Extinction risk by mutational meltdown: Synergistic effects between population regulation and genetic drift 69 Part III: Inbreeding, population and social structure Introductory remarks 87 A. R. Templeton and B. Read Inbreeding: One word, several meanings, much confusion 91 C. Gliddon and J. Goudet The genetic structure of metapopulations and conservation biology 107 vi T.P. Hauser, C. Damgaard and V. Loeschcke Effects of inbreeding in small plant populations: Expectations and implications for conservation 115 A.J. van Noordwijk The interaction of inbreeding depression and environmental stochasticity in the risk of extinction of small populations.... 131 G. de Jong, J.R. de Ruiter and R. Haring Genetic structure of a population with social structure and migration 147 P.M. Brakefield and LJ. Saccheri Guidelines in conservation genetics and the use of the population cage experiments with butterflies to investigate the effects of genetic drift and inbreeding 165 Part IV: Molecular approaches to conservation Introductory remarks 183 P.W. Hedrick and P.S. Miller Rare alleles, MHC and captive breeding 187 P. Ar et ander and J. Fjeldsä Andean tapaculos of the genus Scytalopus (Aves, Rhinocryptidae): A study of speciation using DNA sequence data 205 R.H. Crozier and R.M. Kusmierski Genetic distances and the setting of conservation priorities 227 L. Witting, M.A. McCarthy and V. Loeschcke Multi-species risk analysis, species evaluation and biodiversity conservation 239 Part V: Case studies Introductory remarks 253 R. Bijlsma, N.J. Ouborg and R. van Treuren On genetic erosion and population extinction in plants: A case study in Scabiosa columbaria and Salvia pratensis 255 M.M. Hansen and V. Loeschcke Effects of releasing hatchery-reared brown trout to wild trout populations 273 S.K. Jain Genetics and demography of rare plants and patchily distributed colonizing species 291 vii R.A. Krebs and V. Loeschcke Response to environmental change: Genetic Variation and fitness in Drosophila buzzatii following temperature stress 309 K. Hindar Alternative life histories and genetic conservation 323 Yu.P. Altukhov The principles of population monitoring for conservation genetics 337 Part VI: Genetic resource conservation Introductory remarks 353 A.H.D. Brown and DJ. Schoen Optimal sampling strategies for core collections of plant genetic resources 357 H. Hurka Conservation genetics and the role of botanical gardens 371 J.S.F. Barker Animal breeding and conservation genetics 381 Scenarios Introductory remarks 399 /. Tomiuk and V. Loeschcke A: The genetic monitoring of primate populations for their conservation 401 S.K. Jain B: Heavy metal tolerance, plant evolution and restoration ecology 407 S.K. Jain C: Genetic conservation and plant agriculture 411 J.M. Olesen and S.K. Jain D: Fragmented plant populations and their lost interactions.... 417 S.K. Jain E: Host-pathogen coevolution under in situ conservation 427 S.K. Jain and J. Tomiuk Concluding remarks 431 Subject index 437 Conservation Genetics ed. by V. Loeschcke, J. Tomiuk & S. K. Jain © 1994 Birkhäuser Verlag Basel/Switzerland Extinction risk by mutationa! meltdovvn: Synergistic eifects between population regulation and genetic drift W. Gabriel1 and R. Bürger2 1 Department of Physiological Ecologw Max Planck Institute for Limnolog\\ Postfach 165 D-24302 Plön] Germany 2Institute of Mathematics, University of Vienna, Strudlhofgasse 4, A-I090 Vienna, Austria Summary. The accumulation of deleterious mutations reduces individual and mean popula• tion fitness. Therefore, in the long run, population size is afTected. This facilitates further accumulation of mutations by enhanced genetic drift. Such synergistic interaction then drives the population tö extinction. This mutational meltdovvn pnocess is studied primarily for asexual populations. Recombina- tion cannot stop the meltdovvn in small sexual populations. Independent of the mode of reproduction, the asexual case is relevant for any paternally or maternally inherited trait and for mitochondria and chloroplasts that can be viewed as asexual populations inside cells. The extinction risk is maximal for an intermediate value of the selection coefTicient. Recombination does not destroy this efTect, at least for small populations. In the asexual case, group selection is able to overpower individual selection to establish lineages with low repair capabilities, i.e., highly deleterious mutations. If the expression of deleterious mutations is modifled by the environment, changes in the environment can cause an unexpected increase or decrease in the extinction risk because of the pronounced maximum extinction risk at intermediate values of s. It may be that an environmental management treatment that improves individual fitness, counterintuitively enhances the extinction risk of a population. Introduction In addition to many ecological factors, e.g., random fluctuations of demographic parameters or externally forced perturbations of the envi• ronment, there are also well known genetic effects, e.g., inbreeding depression or loss of genetic variance that can contribute considerably to the extinction risk of populations. Besides these more classical Problems of conservation genetics there is another source of genetic deterioration: the continuous input of slightly deleterious mutations. Lynch and Gabriel (1990) studied the consequences under asexual reproduction, and Gabriel et al. (1991) demonstrated that this mutation load considerably enhances the extinction risk for small sexual popula• tions if it acts together with demographic stochasticity. Recent experi- ments (Houle et al., 1992) confirm the order of magnitude of the mutation load estimated from other data (see Lynch and Gabriel, 1990). 70 On average, each individual genome seems to incur one slightly deleteri• ous mutation per generation. Mutation rate and mutational effect are hard to estimate and the mutation rate might even have been underesti- mated (Kondrashov, 1988). The consequences of the accumulation of deleterious mutations for asexual (or parthenogenetic) organisms are unquestionable, but for sexual species it is still debatable. For which population sizes is the mutational meltdown (Lynch and Gabriel, 1990) an important force if compared to other risks such as fluctuations in the environment? The smaller the population size, the more likely there is a synergistic interaction between many risk factors, i.e., the overall extinc• tion risk might be much higher than expected from considering Single risk factors. To assess the impact of deleterious mutations for populations, classic population genetics is very helpful but can be misleading because most of this theory has been developed for constant (eflective) population sizes. Historically, the main interest has been the change in relative gene frequencies.
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