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Synergism of Natural Selection and Introgression in the Origin of a New Species

Author(s): Grant, Peter R.; Grant, B. Rosemary

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Abstract: This article explores how introgressive hybridization enhances the evolutionary effects of natural selection and how, reciprocally, natural selection can enhance the evolutionary effects of introgression. Both types of interaction were observed during a 40-year study of Darwin’s finches (Geospiza) on the small Galapagos island of Daphne Major. Hybrids, produced rarely by Geospiza fortis (medium ground finch) breeding with Geospiza scandens (cactus finch) and Geospiza fuliginosa (small ground finch), survived and bred as well as the parental species in the past 3 decades. By backcrossing, they increased the standing genetic variation and thereby the evolutionary responsiveness of the populations to natural selection. Natural selection occurred in droughts and oscillated in direction as a result of climatically induced fluctuations in food composition. Introgressive hybridization has led to the formation of a new lineage. It was initiated by a large, introgressed, hybrid male with a unique song and genetic marker that immigrated from the nearby island of Santa Cruz and bred with local hybrids and with G. fortis. All members of the lineage died in the 2003–2005 drought except a brother and a sister, who then bred with each other. Subsequent increase in the lineage was facilitated by selective mortality of the largest G. fortis. Breeding endogamously, the lineage is behaving as a biological species.
Publication Date: May-2014
Citation: Grant, Peter R, Grant, B Rosemary. (2014). Synergism of Natural Selection and Introgression in the Origin of a New Species. The American Naturalist, 183 (5), 671 - 681. doi:10.1086/675496
DOI: doi:10.1086/675496
ISSN: 0003-0147
EISSN: 1537-5323
Pages: 671 - 681
Type of Material: Journal Article
Journal/Proceeding Title: The American Naturalist
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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