Marshall J C, Sites J W
Department of Zoology, Brigham Young University, Provo, UT 84602, USA.
Mol Ecol. 2001 Feb;10(2):435-49. doi: 10.1046/j.1365-294x.2001.01232.x.
The F5 and FM2 chromosome races of the Sceloporus grammicus complex form a hybrid zone in the Mexican state of Hidalgo. Previous studies of this zone have assessed genetic structure by averaging estimates of shape and width across three diagnostic chromosome markers. This approach is likely to mask subtle differences in cline shape among loci (e.g. selected vs. neutral), and obscure any displacement of cline centres (if present). Here we use maximum likelihood methods to construct the best fitting individual clines for three chromosomal markers, and also add two new markers; the mitochondrial DNA (mtDNA) locus, and the nuclear ribosomal DNA (rDNA) repeat. For each locus, hybrid zone models were fitted by cline shape and width, and the position and number of segments describing the centre of the zone. Pairwise comparisons between all clines revealed concordance between chromosomes 2 and 6, but significant discordance in cline structure among all other paired combinations. The concordance of chromosomes 2 and 6 suggests that these clines are maintained by genome-wide forces. The discordance of the chromosome 1 cline suggests an influence of asymmetric introgression, while the mtDNA cline is probably influenced by selection and drift. The rDNA locus reveals a pattern best explained by either extreme asymmetric introgression or gene conversion. The structure of zone indicates that genome-wide processes and locus specific selective forces as well as drift, are operating to different degrees on different loci. The locus-by-locus approach used here permits a finer discrimination among possible mechanisms responsible for the maintenance of the individual clines.
斯氏强棱蜥复合体的F5和FM2染色体族在墨西哥伊达尔戈州形成了一个杂交带。此前对该杂交带的研究通过对三个诊断性染色体标记的形状和宽度估计值求平均值来评估遗传结构。这种方法可能会掩盖不同基因座间渐变群形状的细微差异（例如选择型与中性型），并模糊渐变群中心的任何位移（如果存在的话）。在这里，我们使用最大似然法为三个染色体标记构建最佳拟合的个体渐变群，并且还增加了两个新标记；线粒体DNA（mtDNA）基因座和核糖体DNA（rDNA）重复序列。对于每个基因座，通过渐变群形状和宽度以及描述杂交带中心的片段位置和数量来拟合杂交带模型。所有渐变群之间的成对比较显示，染色体2和6之间具有一致性，但所有其他配对组合的渐变群结构存在显著不一致。染色体2和6的一致性表明，这些渐变群是由全基因组力量维持的。染色体1渐变群的不一致表明存在不对称渐渗的影响，而mtDNA渐变群可能受选择和漂变的影响。rDNA基因座揭示了一种模式，这种模式最好由极端不对称渐渗或基因转换来解释。杂交带的结构表明，全基因组过程、基因座特异性选择力以及漂变在不同基因座上以不同程度发挥作用。这里使用的逐个基因座方法能够更精细地区分维持各个渐变群的可能机制。
