Bossart J L, Scriber J M
Department of Entomology, Michigan State University, East Lansing, Michigan, 48824.
Evolution. 1995 Dec;49(6):1163-1171. doi: 10.1111/j.1558-5646.1995.tb04443.x.
Differential selection in a heterogeneous environment is thought to promote the maintenance of ecologically significant genetic variation. Variation is maintained when selection is counterbalanced by the homogenizing effects of gene flow and random mating. In this study, we examine the relative importance of differential selection and gene flow in maintaining genetic variation in Papilio glaucus. Differential selection on traits contributing to successful use of host plants (oviposition preference and larval performance) was assessed by comparing the responses of southern Ohio, north central Georgia, and southern Florida populations of P. glaucus to three hosts: Liriodendron tulipifera, Magnolia virginiana, and Prunus serotina. Gene flow among populations was estimated using allozyme frequencies from nine polymorphic loci. Significant genetic differentiation was observed among populations for both oviposition preference and larval performance. This differentiation was interpreted to be the result of selection acting on Florida P. glaucus for enhanced use of Magnolia, the prevalent host in Florida. In contrast, no evidence of population differentiation was revealed by allozyme frequencies. F -values were very small and Nm, an estimate of the relative strengths of gene flow and genetic drift, was large, indicating that genetic exchange among P. glaucus populations is relatively unrestricted. The contrasting patterns of spatial differentiation for host-use traits and lack of differentiation for electrophoretically detectable variation implies that differential selection among populations will be counterbalanced by gene flow, thereby maintaining genetic variation for host-use traits.
在异质环境中的差异选择被认为有助于维持具有生态意义的遗传变异。当选择被基因流和随机交配的同质化效应所抵消时，变异得以维持。在本研究中，我们检验了差异选择和基因流在维持北美黄凤蝶（Papilio glaucus）遗传变异中的相对重要性。通过比较俄亥俄州南部、佐治亚州中北部和佛罗里达州南部的北美黄凤蝶种群对三种寄主植物：北美鹅掌楸（Liriodendron tulipifera）、弗吉尼亚木兰（Magnolia virginiana）和黑樱桃（Prunus serotina）的反应，评估了对有助于成功利用寄主植物的性状（产卵偏好和幼虫表现）的差异选择。利用来自九个多态位点的等位酶频率估计种群间的基因流。在产卵偏好和幼虫表现方面，种群间均观察到显著的遗传分化。这种分化被解释为是由于选择作用于佛罗里达州的北美黄凤蝶，使其更多地利用佛罗里达州普遍存在的寄主植物木兰。相比之下，等位酶频率未显示出种群分化的证据。F值非常小，而作为基因流和遗传漂变相对强度估计值的Nm很大，这表明北美黄凤蝶种群间的基因交换相对不受限制。寄主利用性状的空间分化模式与电泳可检测变异缺乏分化形成对比，这意味着种群间的差异选择将被基因流所抵消，从而维持寄主利用性状的遗传变异。
