Unpredictable Evolution in a 30-Year Study of Darwin's Finches

Evolution can be predicted in the short term from a knowledge of selection and inheritance. However, in the long term evolution is unpredictable because environments, which determine the directions and magnitudes of selection coefficients, fluctuate unpredictably. These two features of evolution, the predictable and unpredictable, are demonstrated in a study of two populations of Darwin's finches on the Galápagos island of Daphne Major. From 1972 to 2001,Geospiza fortis (medium ground finch) and Geospiza scandens (cactus finch) changed several times in body size and two beak traits. Natural selection occurred frequently in both species and varied from unidirectional to oscillating, episodic to gradual. Hybridization occurred repeatedly though rarely, resulting in elevated phenotypic variances in G. scandens and a change in beak shape. The phenotypic states of both species at the end of the 30-year study could not have been predicted at the beginning. Continuous, long-term studies are needed to detect and interpret rare but important events and nonuniform evolutionary change.

[1]  T. Price.  SEXUAL SELECTION ON BODY SIZE, TERRITORY AND PLUMAGE VARIABLES IN A POPULATION OF DARWIN'S FINCHES , 1984, Evolution; international journal of organic evolution.

[2]  Charles R. Brown,et al.  Ecology and Evolution of Darwin’s Finches , 2001, Heredity.

[3]  Barbraud.  Natural selection on body size traits in a long‐lived bird, the snow petrel Pagodroma nivea , 1999 .

[4]  F. Maytag.  Evolution , 1996, Arch. Mus. Informatics.

[5]  D. Schrag,et al.  Abrupt shift in subsurface temperatures in the tropical pacific associated with changes in El Nino , 1998, Science.

[6]  P. Grant.  Hybridization of Darwin's Finches on Isla Daphne Major, Galapagos , 1993 .

[7]  L. Keller.  INBREEDING AND ITS FITNESS EFFECTS IN AN INSULAR POPULATION OF SONG SPARROWS (MELOSPIZA MELODIA) , 1998, Evolution; international journal of organic evolution.

[8]  C. Brown,et al.  Four decades of inversion polymorphism in Drosophila pseudoobscura. , 1991, Proceedings of the National Academy of Sciences of the United States of America.

[9]  V. Loeschcke,et al.  Population Biology and Evolution , 1984, Proceedings in Life Sciences.

[10]  M. Cody,et al.  Long-term studies of vertebrate communities , 1997 .

[11]  P. Ehrlich,et al.  THE POPULATION BIOLOGY OF THE BUTTERFLY EUPHYDRY AS EDITH A. III. SELECTION AND THE PHENETICS OF THE JASPER RIDGE COLONY , 1966, Evolution; international journal of organic evolution.

[12]  B. Grant,et al.  Hybridization of Bird Species , 1992, Science.

[13]  M. Rose,et al.  PERSPECTIVE: REVERSE EVOLUTION , 2001, Evolution; international journal of organic evolution.

[14]  Peter R. Grant,et al.  DEMOGRAPHY AND THE GENETICALLY EFFECTIVE SIZES OF TWO POPULATIONS OF DARWIN'S FINCHES' , 1992 .

[15]  L. Gustafsson,et al.  Hybridization and adaptive mate choice in flycatchers , 2001, Nature.

[16]  Sokal Rr,et al.  Biometry: the principles and practice of statistics in biological research 2nd edition. , 1981 .

[17]  J. Endler.  Natural selection in the wild , 1987 .

[18]  P. Grant,et al.  Intense Natural Selection in a Population of Darwin's Finches (Geospizinae) in the Gal�pagos , 1981, Science.

[19]  P. Grant,et al.  Oscillating selection on Darwin's finches , 1987, Nature.

[20]  Michael Travisano,et al.  Adaptive radiation in a heterogeneous environment , 1998, Nature.

[21]  Selection often overrides the effects of random processes in island populations of Philaenus spumarius (Homoptera) , 2001 .

[22]  M. Arnold.  Natural Hybridization and Evolution , 1997 .

[23]  Keith A. Gardner,et al.  EVOLUTIONARY CHANGES OVER THE FIFTY‐YEAR HISTORY OF A HYBRID POPULATION OF SUNFLOWERS (HELIANTHUS) , 2000, Evolution; international journal of organic evolution.

[24]  L. Kruuk,et al.  Cryptic evolution in a wild bird population , 2001, Nature.

[25]  Marcel E. Visser,et al.  Warmer springs lead to mistimed reproduction in great tits (Parus major) , 1998, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[26]  Julie R. Etterson,et al.  Constraint to Adaptive Evolution in Response to Global Warming , 2001, Science.

[27]  Peter Kareiva,et al.  Biotic interactions and global change. , 1993 .

[28]  B. Sinervo,et al.  Density cycles and an offspring quantity and quality game driven by natural selection , 2000, Nature.

[29]  L. Kruuk,et al.  Phenotypic Selection on a Heritable Size Trait Revisited , 2001, The American Naturalist.

[30]  D. Berrigan,et al.  Strength and tempo of directional selection in the wild , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[31]  B. Grant,et al.  Heritability of morphological traits in Darwin’s Finches: misidentified paternity and maternal effects , 2001, Heredity.

[32]  A. Busalacchi,et al.  Origin of upper-ocean warming and El Niño change on decadal scales in the tropical Pacific Ocean , 1998, Nature.

[33]  B. Grant,et al.  Non–random fitness variation in two populations of Darwin's finches , 2000, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[34]  Js Jones,et al.  Gene frequency changes in Cepaea snails on the Marlborough Downs over 25 years , 1998 .

[35]  M. Brooke,et al.  Evolutionary Dynamics of a Natural Population: The Large Cactus Finch of the Galapagos , 1989 .

[36]  F. James Rohlf,et al.  Biometry: The Principles and Practice of Statistics in Biological Research , 1969 .

[37]  D. Jones.  50 years of studying the scarlet tiger moth. , 1989, Trends in ecology & evolution.

[38]  J. M. Hoekstra,et al.  The Strength of Phenotypic Selection in Natural Populations , 2001, The American Naturalist.

[39]  P. Grant,et al.  Recurrent patterns of natural selection in a population of Darwin's finches , 1984, Nature.

[40]  F. H. Rodd,et al.  Evaluation of the Rate of Evolution in Natural Populations of Guppies (Poecilia reticulata) , 1997, Science.

[41]  B. Grant,et al.  PREDICTING MICROEVOLUTIONARY RESPONSES TO DIRECTIONAL SELECTION ON HERITABLE VARIATION , 1995, Evolution; international journal of organic evolution.

[42]  J. H. Brown,et al.  Complex species interactions and the dynamics of ecological systems: long-term experiments. , 2001, Science.

[43]  G. Likens,et al.  Long-Term Studies in Ecology: Approaches and Alternatives , 1990 .

[44]  B. Grant,et al.  PHENOTYPIC AND GENETIC EFFECTS OF HYBRIDIZATION IN DARWIN'S FINCHES , 1994, Evolution; international journal of organic evolution.

[45]  Sarah Mae Sincero.  Heredity , 1875, Nature.

[46]  J. Wiens.  Long-term studies of vertebrate communities , 1997 .