新物种是怎样形成的?物种形成难以直接观测,因为它是一个漫长的过程。人们曾在理论上分为,当一个物种的种群相互分开、去适应不同环境时,它们在杂交方面就会变得不太成功,就可能形成新物种。在一个实验中,研究人员使用了两个菌种的酵母,它们在能够加快物种形成的实验室条件下繁殖。该实验证实,适应于不同环境的种群的杂交与全部适应于同一环境的种群的杂交相比,前者的繁殖能力差一些(适应性差一些)。这是趋异适应与生殖隔离的发展之间的一个根本性联系的直接证据。
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: jdettman@utm.utoronto.ca).
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.