40 Years of Evolution: Darwin's Finches on Daphne Major Island

40 Years of Evolution: Darwin's Finches on Daphne Major Island

Language: English

Pages: 432

ISBN: 0691160465

Format: PDF / Kindle (mobi) / ePub


Renowned evolutionary biologists Peter and Rosemary Grant have produced landmark studies of the Galápagos finches first made famous by Charles Darwin. In How and Why Species Multiply, they offered a complete evolutionary history of Darwin's finches since their origin almost three million years ago. Now, in their richly illustrated new book, 40 Years of Evolution, the authors turn their attention to events taking place on a contemporary scale. By continuously tracking finch populations over a period of four decades, they uncover the causes and consequences of significant events leading to evolutionary changes in species.

The authors used a vast and unparalleled range of ecological, behavioral, and genetic data--including song recordings, DNA analyses, and feeding and breeding behavior--to measure changes in finch populations on the small island of Daphne Major in the Galápagos archipelago. They find that natural selection happens repeatedly, that finches hybridize and exchange genes rarely, and that they compete for scarce food in times of drought, with the remarkable result that the finch populations today differ significantly in average beak size and shape from those of forty years ago. The authors' most spectacular discovery is the initiation and establishment of a new lineage that now behaves as a new species, differing from others in size, song, and other characteristics. The authors emphasize the immeasurable value of continuous long-term studies of natural populations and of critical opportunities for detecting and understanding rare but significant events.

By following the fates of finches for several generations, 40 Years of Evolution offers unparalleled insights into ecological and evolutionary changes in natural environments.

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— Process that is dependent on population density, such as offspring growth or mortality. Dermis — Skin tissue. Despeciation — Speciation in reverse, when sister species exchange genes through introgressive hybridization, leading to the elimination of the differences between them. Diatoms — Microscopic one-celled or colonial algae with silica walls. Dickkopf3 (Dkk3) — A glycoprotein that acts as a signaling molecule implicated in beak development. Discriminant function analysis — Statistical

by a community of seed predators. Evolution 67: 157–169. [226] Billick, I., and Price, M. V., eds. 2010. Ecology of Place: Contributions of Place-Based Research to Ecological Understanding. University of Chicago Press, Chicago, IL. [310, 311] Billing, A. M., A. M. Lee, S. Skjelseth, A. A. Borg, M. C. Hale, J. Slate, H. Pärn, T. H. Ringsby, B-E. Sæther, and H. Jensen. 2012. Evidence of inbreeding depression but not inbreeding avoidance in a natural house sparrow population. Mol. Ecol. 21:

adjustable. The opportunities for repeated breeding with large clutches arise from strong pulses of food production in some very wet years, coupled with low breeding density following heavy mortality in the preceding dry season. In this respect the finches on Daphne resemble birds in temperate regions (Ashmole 1963, Ricklefs 1980, Grant and Grant 1980b) and in the seasonally arid coastal region of Ecuador (Marchant 1958), in marked contrast to the stable populations under density-dependent

backcrossing occurred from scandens × fortis hybrids to scandens. The second shift occurred when we had no pedigree data, and therefore we do not know how it occurred. It resulted in the generation of individuals in previously unoccupied morphological space. Notice in figure 10.3, for example, that in 1991 there were no scandens with beak lengths of 13–14 mm that had beak depths greater than 9.5 mm, but in 2012 there were plenty. The most likely explanation is a change in mating patterns of

(chapters 3 and 9), in agreement with the introgression-selection balance model in figure 9.1. This appears to have changed in the second half of the study, in the light of a doubling of phenotypic variation in both species from beginning to the end (fig. 10.6) and an unmeasured increase in additive genetic variance from introgression. The chief implication is that selection, which opposes increases in variation (fig. 9.1), must be relatively weak, and differences between species in variation

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