Nosil Patrik
Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Am Nat. 2007 Feb;169(2):151-62. doi: 10.1086/510634. Epub 2007 Jan 2.
Theoretical and empirical studies have demonstrated that divergent natural selection can promote the evolution of reproductive isolation. Three unresolved questions concern the types of reproductive barriers involved, the role of geography, and the factors determining the extent of progress toward complete speciation. Here I synthesize studies of Timema cristinae host plant ecotypes to address these issues. The approach is to compare the magnitude of multiple reproductive barriers among different ecological and geographic scenarios, where pairs of populations within each scenario are the unit of replication. Application of this approach to T. cristinae revealed that divergent host adaptation can promote the evolution of diverse reproductive barriers, including those that are not inherently ecological. Gene flow in parapatry tended to constrain divergence, with the notable exception of the reinforcement of sexual isolation. Thus, geography affected progress toward speciation but did not influence all reproductive barriers in the same way. Studies of any single pair of taxa often capture only certain stages of the speciation process. For example, reproductive isolation between T. cristinae ecotypes is incomplete, and so only the stages before the completion of speciation have been examined. Studies of more divergent taxa within the genus are required to determine the factors that complete speciation.
理论和实证研究表明，分歧性自然选择能够推动生殖隔离的进化。三个尚未解决的问题涉及所涉及的生殖障碍类型、地理因素的作用以及决定向完全物种形成进展程度的因素。在此，我综合了对克氏细颈螳蝎（Timema cristinae）寄主植物生态型的研究来探讨这些问题。方法是比较不同生态和地理情景下多种生殖障碍的程度，其中每个情景中的种群对作为重复单元。将这种方法应用于克氏细颈螳蝎表明，不同的寄主适应性能够促进多种生殖障碍的进化，包括那些并非本质上属于生态性的障碍。在邻域分布中基因流往往会限制分歧，但性隔离的强化是一个显著例外。因此，地理因素影响物种形成的进程，但并非以相同方式影响所有生殖障碍。对任何一对分类单元的研究通常仅捕捉到物种形成过程的某些阶段。例如，克氏细颈螳蝎生态型之间的生殖隔离并不完全，所以仅研究了物种形成完成之前的阶段。需要对该属内分歧更大的分类单元进行研究，以确定完成物种形成的因素。
