A fase secundária de contato da especiação alopátrica nos tentilhões de Darwin

The secondary contact phase of allopatric speciation in Darwin's finches

Peter R. Grant 1 and B. Rosemary Grant

- Author Affiliations

Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544-1003

Contributed by Peter R. Grant, October 12, 2009 (sent for review September 17, 2009)

Abstract

Speciation, the process by which two species form from one, involves the development of reproductive isolation of two divergent lineages. Here, we report the establishment and persistence of a reproductively isolated population of Darwin's finches on the small Galápagos Island of Daphne Major in the secondary contact phase of speciation. In 1981, an immigrant medium ground finch (Geospiza fortis) arrived on the island. It was unusually large, especially in beak width, sang an unusual song, and carried some Geospiza scandens alleles. We followed the fate of this individual and its descendants for seven generations over a period of 28 years. In the fourth generation, after a severe drought, the lineage was reduced to a single brother and sister, who bred with each other. From then on this lineage, inheriting unusual song, morphology, and a uniquely homozygous marker allele, was reproductively isolated, because their own descendants bred with each other and with no other member of the resident G. fortis population. These observations agree with some expectations of an ecological theory of speciation in that a barrier to interbreeding arises as a correlated effect of adaptive divergence in morphology. However, the important, culturally transmitted, song component of the barrier appears to have arisen by chance through an initial imperfect copying of local song by the immigrant. The study reveals additional stochastic elements of speciation, in which divergence is initiated in allopatry; immigration to a new area of a single male hybrid and initial breeding with a rare hybrid female.

immigration inbreeding introgression

Footnotes

1To whom correspondence should be addressed. E-mail: prgrant@princeton.edu

Author contributions: P.R.G. and B.R.G. designed research, performed research, analyzed data, and wrote the paper.

The authors declare no conflict of interest.

+++++

PDF gratuito do artigo aqui.