Magi Mike's Blog

Another WordPress blog about politics and religion

Speciation Observed in Darwin’s Finches

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Well those evolutionary theory deniers who constantly claim that speciation, the process by which two species form from one, has never been observed can be silenced. Speciation involves the development of reproductive isolation of two divergent evolutionary lineages. Peter R Grant and B Rosemary Grant 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. The researchers followed the fate of this bird 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. 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.

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Written by mikemagee

22 January, 2010 at 10:40 pm

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