Peter R. Grant - 40 Years of Evolution: Darwins Finches on Daphne Major Island

40 Years of Evolution

40 Years of Evolution

Peter R. Grant and B. Rosemary Grant

Princeton University Press

Princeton and Oxford

Copyright 2014 by Princeton University Press

Published by Princeton University Press, 41 William Street, Princeton, New Jersey 08540

In the United Kingdom: Princeton University Press, 6 Oxford Street, Woodstock, Oxfordshire OX20 1TW

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Library of Congress Cataloging-in-Publication Data

Grant, Peter R., 1936

Forty years of evolution : Darwins Finches on Daphne Major Island / Peter R. Grant and B. Rosemary Grant.

pages cm

Includes bibliographical references and index.

ISBN 978-0-691-16046-7 (hardback : alk. paper) 1. Ground finchesEvolutionGalapagos Islands. 2. Bird populationsGalapagos Islands. 3. BirdsEvolutionGalapagos Islands. I. Grant, B.

Rosemary. II. Title.

QL696.P246G7324 2014
598.07232098665dc23
2013018007

British Library Cataloging-in-Publication Data is available

This book has been composed in ITC Caslon 224

Printed on acid-free paper.

Printed in the United States of America

2 4 6 8 10 9 7 5 3 1

To the next generation: Nicola and Thalia

And the next one: Rajul, Olivia, Anjali, and Devon

And succeeding ones

Daphne Major

She looms from the hyaline like some mutant barnaclefrond once a pillar of smoke, operculum blown offthat has assumed a couchant pose, waiting for the searchers with mist-nets and calipers to return each year who pit the caltrop against magnirostris and scratch protean generations from her flank, until she blows again or sounds and sinks back to Gondwanalands deep ocean drift

(Weston 2005, p. 49)

The sight of Daphne Major conveys something like this [passage of time] to us, even in the first glance over the water, or in the last, as it revolves like a wood chip in the wake of the boat. We know we are looking at a place that was here before we came and will remain when we are gone. The very island will sink someday, and another will rise when it is drowned.

(Weiner 1994, p. 303)

Illustrations

Tables

Boxes

Preface

D ARWINS ORIGIN OF SPECIES (1859, p. 1) begins: When on board H.M.S. Beagle, as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of speciesthat mystery of mysteries, as it has been called by one of our greatest philosophers. We followed in his footsteps 138 years after his visit to the Galpagos, with the same quest in mind. Our book describes what we learned by studying Darwins finches ().

Genetic variation is the raw material for evolution. Although much has been learned about genetic variation from theoretical and laboratory research, long-term field studies in natural environment have been relatively neglected. Knowledge of how genetic and phenotypic variation interacts with environmental variation is fundamentally important for understanding evolution in nature. It can be achieved by long-term field studies of evolution with well-chosen organisms in well-chosen environments when coupled with the benefits of laboratory science. This is what we have attempted to do. By taking a multidimensional approach to questions of evolution and speciation, carefully documenting genetic, ecological, and behavioral factors responsible for evolution of finches across 40 years, we have made discoveries about speciation far beyond our initial expectations. And although finches are the focal organisms of the study, the principles of their evolution apply broadly to all organisms.

These are exciting times to be an evolutionary biologist. Changes in technology are proceeding at an ever-increasing pace, giving us the tools for expanding our knowledge and understanding of how evolution occurs in the natural world. In view of this it is worth reflecting on the state of knowledge in 1973 (Mayr 1970, Dobzhansky 1970), on the methods and tools available for evolutionary investigations at that time, and the transformation that studies of speciation have undergone since then. Techniques we take for granted now did not exist. Electrophoresis (Hubby and Lewontin 1966) was only just becoming widely available as a method of detecting allozyme variation if the appropriate buffers could be worked out. It required a power source, which ruled it out for most studies on uninhabited islands. Cladistics (Hennig 1966) had yet to shake the foundations of phylogenetic reconstruction and interpretation. Personal computers had yet to be invented; we were the handmaidens of university mainframes. Statistical programs for the analysis of complex data had not been invented either, and the revolution in molecular biology, including evodevo, lay far off in the future. Whole genomes were conceivable, but their sequences were not. Now we do things we could not anticipate doing at the outset; for example, we study genes, their expression patterns and regulation, and we infer from molecular data the time when events took place in the past. Our account of evolution on Daphne reflects the expanding knowledge brought about by the development of new methods as the study progressed.

Fig. P.1 The four species of finches. Upper left: Small Ground Finch, G. fuliginosa. Upper right: Medium Ground Finch, G. fortis. Lower left: Large Ground Finch, G. magnirostris. Lower right: Cactus Finch, G. scandens. From Grant and Grant 2008a).

Fig. P.2 The two Daphnes. Left: Daphne Major, with Daphne Minor (Chica) in the background (D. Parer and E. Parer-Cook). Right: Daphne Minor, 1976. Daphne Minor has been climbed once, with ropes. Two immature fortis banded on Daphne Major were seen at the top (Grant et al. 1980).

Fig. P.3 Map of Galpagos. From Grant and Grant 2008a.

Fig. P.4 Phenotypic variation in the G. fortis population on Daphne.

In the absence of fossils, answers to questions about speciation in the past have to be sought with living organisms by looking backward in time. Typically this is done by using information on contemporary populations to test the assumptions of historical hypotheses: a retrospective analysis. We followed this path with a combination of field studies of short duration on many islands and a decade-long study on Genovesa. We concentrated almost entirely on the six ground finch species in the genus