Parchman Thomas L, Benkman Craig W, Britch Seth C
Department of Biology, MSC 3AF, New Mexico State University, Las Cruces, New Mexico 88003-8001, USA.
Mol Ecol. 2006 Jun;15(7):1873-87. doi: 10.1111/j.1365-294X.2006.02895.x.
Incipient species groups or young adaptive radiations such as crossbills (Aves: Loxia) present the opportunity to investigate directly the processes occurring during speciation. New World crossbills include white-winged crossbills (Loxia leucoptera), Hispaniolan crossbills (Loxia megaplaga), and red crossbills (Loxia curvirostra complex), the last of which is comprised of at least nine morphologically and vocally differentiated forms ('call types') where divergent natural selection for specialization on different conifer resources has been strongly implicated as driving diversification. Here we use amplified fragment length polymorphism (AFLP) markers to investigate patterns of genetic variation across populations, call types, and species of New World crossbills. Tree-based analyses using 440 AFLP loci reveal strongly supported clustering of the formally recognized species, but did not separate individuals from the eight call types in the red crossbill complex, consistent with recent divergence and ongoing gene flow. Analyses of genetic differentiation based on inferred allele frequency variation however, reveal subtle but significant levels of genetic differentiation among the different call types of the complex and indicate that between call-type differentiation is greater than that found among different geographic locations within call types. Interpreted in light of evidence of divergent natural selection and strong premating reproductive isolation, the observed genetic differentiation suggests restricted gene flow among sympatric call types consistent with the early stages of ecological speciation.
初现的物种组或年轻的适应性辐射类群，如交嘴雀（鸟类：交嘴雀属），为直接研究物种形成过程提供了契机。新大陆交嘴雀包括白翅交嘴雀（Loxia leucoptera）、伊斯帕尼奥拉岛交嘴雀（Loxia megaplaga）和红交嘴雀（Loxia curvirostra复合种），其中红交嘴雀至少由九种形态和鸣声不同的类型（“叫声类型”）组成，在不同针叶树资源上的特化差异自然选择被认为是推动其多样化的重要因素。在此，我们使用扩增片段长度多态性（AFLP）标记来研究新大陆交嘴雀种群、叫声类型和物种间的遗传变异模式。基于440个AFLP位点的树形分析显示，正式认可的物种聚类得到有力支持，但并未将红交嘴雀复合种中八个叫声类型的个体区分开，这与近期的分化和持续的基因流一致。然而，基于推断的等位基因频率变异进行的遗传分化分析表明，该复合种不同叫声类型之间存在细微但显著的遗传分化水平，且表明叫声类型间的分化大于同一叫声类型内不同地理位置间的分化。结合差异自然选择和强烈的交配前生殖隔离的证据来看，观察到的遗传分化表明同域叫声类型间的基因流受限，这与生态物种形成的早期阶段相符。
