新物种是怎么形成的？这个问题是演化生物学中一个人们不断研究的问题。生殖分离会怎样通过根据一个简单的、由生态环境决定的特征（在本研究案例中为棘鱼的身体大小）所做的自然选择来演化？关于这个问题的一个明确的实例，为生态环境在物种形成中所起的作用提供了一个新的例子。实验所用的鱼来自不同的洲和不同的海洋，把它们一起放进位于美国威斯康星州Whitewater或加拿大温哥华的实验池中。决定这些独立演化的鱼类种群间的交配匹配性的因素是身体大小。所以，物种形成似乎基本上可作为基于少量性状所做的选择的一种副产品出现。
Nature 429, 294 - 298 (20 May 2004); doi:10.1038/nature02556
Evidence for ecology's role in speciation
JEFFREY S. MCKINNON1, SEIICHI MORI2, BENJAMIN K. BLACKMAN3,*, LIOR DAVID3,*, DAVID M. KINGSLEY3, LEIA JAMIESON1, JENNIFER CHOU1 & DOLPH SCHLUTER4
1 Biological Sciences, University of Wisconsin-Whitewater, Whitewater, Wisconsin 53190, USA
2 Biological Laboratory, Gifu-Keizai University, Ogaki, Gifu prefecture 503-8550, Japan
3 HHMI and Stanford University School of Medicine, Beckman Center B300, 279 Campus Drive, Stanford, California 94305-5329, USA
4 Department of Zoology and Centre for Biodiversity, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
* Present addresses: Department of Biology, Indiana University, Jordan Hall Rm 325, 1001 E. 3rd Street, Bloomington, Indiana 47405, USA (B.K.B,); Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, USA (L.D.)
Correspondence and requests for materials should be addressed to J.S.M. (mckinnoj@uww.edu).
A principal challenge in testing the role of natural selection in speciation is to connect the build-up of reproductive isolation between populations to divergence of ecologically important traits. Demonstrations of 'parallel speciation', or assortative mating by selective environment, link ecology and isolation, but the phenotypic traits mediating isolation have not been confirmed. Here we show that the parallel build-up of mating incompatibilities between stickleback populations can be largely accounted for by assortative mating based on one trait, body size, which evolves predictably according to environment. In addition to documenting the influence of body size on reproductive isolation for stickleback populations spread across the Northern Hemisphere, we have confirmed its importance through a new experimental manipulation. Together, these results suggest that speciation may arise largely as a by-product of ecological differences and divergent selection on a small number of phenotypic traits.
