Szymura Jacek M, Barton Nicholas H
Department of Comparative Anatomy, Jagiellonian University, ul. Karaşia 6, Krakow, 30-060, POLAND.
Department of Genetics and Biometry, University College London, 4 Stephenson Way, London, NW1 2HE, UK.
Evolution. 1991 Mar;45(2):237-261. doi: 10.1111/j.1558-5646.1991.tb04400.x.
We compare the pattern of morphological and electrophoretic variation in the hybrid zone between Bombina bombina and B. variegata across two transects: one near Cracow and one 200 km away, near Przemyśl in southeastern Poland. Morphological variation across the Przemyśl transect had been surveyed more than 50 years ago; though we found a significant shift at one site, there is no evidence for gross movement over this period. Morphological and electrophoretic changes coincide, and the average shape of the clines is the same across both transects. At the center, most of the change in frequency of six diagnostic allozymes occurs within w = 6.05 km (2-unit support limits 5.56-6.54 km). These steep gradients are generated not by selection on the allozymes themselves, but by associations with other loci: though these markers are unlinked, they are in strong linkage disequilibrium with each other [R = D/√pquv = 0.22 (0.15-0.29) at the center]. Disequilibria are broken up as alleles diffuse away from the zone and flow into the new genetic background. The net barrier to the flow of genes from bombina into variegata, which is generated by these disequilibria, is B = 51 (22-81) km. The fitness of hybrids must be substantially reduced to produce such a barrier [W̄ /W̄ = 0.58 (0.54-0.68)], and this selection must be spread over many loci [N = 55 (26-88)]. Alleles introgress significantly less far than would be expected from the age of the zone and the estimated dispersal rate [σ = 0.99 (0.82-1.14) km gen. ]: this implies selection of s = 0.37 (0.15-0.58)% on the enzymes themselves. There is weak but significant linkage disequilibrium well away from the center of the zone; this, together with the presence of parental and F genotypes, suggests some long-range migration. However, such migration is not likely to cause significant introgression.
我们比较了欧洲产婆蟾（Bombina bombina）和多彩产婆蟾（B. variegata）杂交区域内形态学和电泳变异模式，该杂交区域分布于两条样带：一条靠近克拉科夫，另一条在200公里以外，位于波兰东南部的普热梅希尔附近。50多年前已对普热梅希尔样带的形态学变异进行过调查；尽管我们在一个位点发现了显著变化，但没有证据表明在此期间有大规模移动。形态学和电泳变化一致，两条样带的渐变群平均形状相同。在中心区域，六种诊断性等位酶频率的大部分变化发生在w = 6.05公里范围内（2个单位的支持极限为5.56 - 6.54公里）。这些陡峭的梯度不是由对等位酶本身的选择产生的，而是由与其他基因座的关联产生的：尽管这些标记是不连锁的，但它们彼此处于强连锁不平衡状态[在中心区域R = D/√pquv = 0.22（0.15 - 0.29）]。当等位基因从该区域扩散并流入新的遗传背景时，不平衡状态被打破。由这些不平衡产生的从欧洲产婆蟾到多彩产婆蟾的基因流动净障碍为B = 51（22 - 81）公里。杂种的适应性必须大幅降低才能产生这样的障碍[W̄ /W̄ = 0.58（0.54 - 0.68）]，并且这种选择必须分布在许多基因座上[N = 55（26 - 88）]。等位基因渗入的距离明显小于根据该区域的年龄和估计的扩散率所预期的距离[σ = 0.99（0.82 - 1.14）公里/世代]：这意味着对酶本身的选择系数为s = 0.37（0.15 - 0.58）%。在远离区域中心的地方存在微弱但显著的连锁不平衡；这与亲本和F基因型的存在一起，表明存在一些远距离迁移。然而，这种迁移不太可能导致显著的基因渗入。
