新物種是怎樣形成的,？物種形成難以直接觀測,，因為它是一個漫長的過程,。人們曾在理論上分為,，當(dāng)一個物種的種群相互分開,、去適應(yīng)不同環(huán)境時，它們在雜交方面就會變得不太成功,，就可能形成新物種,。在一個實驗中,，研究人員使用了兩個菌種的酵母，它們在能夠加快物種形成的實驗室條件下繁殖,。該實驗證實,，適應(yīng)于不同環(huán)境的種群的雜交與全部適應(yīng)于同一環(huán)境的種群的雜交相比，前者的繁殖能力差一些（適應(yīng)性差一些）,。這是趨異適應(yīng)與生殖隔離的發(fā)展之間的一個根本性聯(lián)系的直接證據(jù),。
部分英文原文：
Nature 447, 585-588 (31 May 2007) | doi:10.1038/nature05856; Received 2 November 2006; Accepted 12 April 2007
Incipient speciation by divergent adaptation and antagonistic epistasis in yeast
Jeremy R. Dettman1, Caroline Sirjusingh1, Linda M. Kohn1 & James B. Anderson1
Department of Ecology & Evolutionary Biology, University of Toronto, Mississauga, Ontario, L5L 1C6, Canada
Correspondence to: Jeremy R. Dettman1 Correspondence and requests for materials should be addressed to J.R.D. (Email: [email protected]).
Abstract
Establishing the conditions that promote the evolution of reproductive isolation and speciation has long been a goal in evolutionary biology1, 2, 3. In ecological speciation, reproductive isolation between populations evolves as a by-product of divergent selection and the resulting environment-specific adaptations4, 5, 6. The leading genetic model of reproductive isolation predicts that hybrid inferiority is caused by antagonistic epistasis between incompatible alleles at interacting loci1, 7. The fundamental link between divergent adaptation and reproductive isolation through genetic incompatibilities has been predicted1, 4, 5, but has not been directly demonstrated experimentally. Here we empirically tested key predictions of speciation theory by evolving the initial stages of speciation in experimental populations of the yeast Saccharomyces cerevisiae. After replicate populations adapted to two divergent environments, we consistently observed the evolution of two forms of postzygotic isolation in hybrids: reduced rate of mitotic reproduction and reduced efficiency of meiotic reproduction. This divergent selection resulted in greater reproductive isolation than parallel selection, as predicted by the ecological speciation theory. Our experimental system allowed controlled comparison of the relative importance of ecological and genetic isolation, and we demonstrated that hybrid inferiority can be ecological and/or genetic in basis. Overall, our results show that adaptation to divergent environments promotes the evolution of reproductive isolation through antagonistic epistasis, providing evidence of a plausible common avenue to speciation and adaptive radiation in nature.
