Nürnberger Beate, Barton Nick, MacCallum Catriona, Gilchrist Jason, Appleby Michael
Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh, EH9 3JT, United Kingdom.
Evolution. 1995 Dec;49(6):1224-1238. doi: 10.1111/j.1558-5646.1995.tb04449.x.
Observations on the means, variances, and covariances of quantitative traits across hybrid zones can give information similar to that from Mendelian markers. In addition, they can identify particular traits through which the cline is maintained. We describe a survey of six traits across the hybrid zone between Bombina bombina and Bombina variegata (Amphibia: Discoglossidae) near Pešćenica in Croatia. We obtained laboratory measuments of the belly pattern, skin thickness, mating call, skeletal form, egg size, and the developmental time of tadpoles. Although offspring from hybrid populations showed no evidence of reduced viability, a third of the F families failed completely, irrespective of the direction of the cross. All traits differed significantly between the taxa. Clines in belly pattern, skin thickness, mating call, and skeletal form were closely concordant with clines in four diagnostic enzyme loci. However, the cline in developmental time was displaced towards bombina, and the cline in egg size was displaced towards variegata. This discordance could be because the traits are not inherited additively or because they are subject to different selection pressures. We favor the latter explanation in the case of developmental time. We show that moderate selection acting directly on a trait suffices to shift its position; rather stronger selection is needed to change its width appreciably. Within hybrid populations, there are significant associations among quantitative traits, and between traits and enzymes. Phenotypic variances also increase in hybrid populations. These observations can be explained by linkage disequilibria among the underlying loci. However, the average magnitude of the covariance between traits is about half that expected from the linkage disequilibria between enzyme loci. The discrepancy is not readily explained by nonadditive gene action. This puzzle is now unresolved and calls for further investigation.
对杂交区域内数量性状的均值、方差和协方差进行观察，能够提供与孟德尔标记类似的信息。此外，这些观察还能识别出维持渐变群的特定性状。我们描述了一项对克罗地亚佩什契尼察附近的欧洲产婆蟾（Bombina bombina）和斑产婆蟾（Bombina variegata，两栖纲：盘舌蟾科）杂交区域内六个性状的调查。我们获得了腹部图案、皮肤厚度、交配叫声、骨骼形态、卵大小以及蝌蚪发育时间的实验室测量数据。尽管杂交种群的后代没有显示出生存力降低的迹象，但三分之一的F家族完全失败，无论杂交方向如何。所有性状在两个分类单元之间都存在显著差异。腹部图案、皮肤厚度、交配叫声和骨骼形态的渐变群与四个诊断酶位点的渐变群密切一致。然而，发育时间的渐变群向欧洲产婆蟾偏移，卵大小的渐变群向斑产婆蟾偏移。这种不一致可能是因为这些性状不是以加性方式遗传，或者是因为它们受到不同的选择压力。对于发育时间的情况，我们倾向于后一种解释。我们表明，直接作用于一个性状的适度选择足以改变其位置；而要明显改变其宽度则需要更强的选择。在杂交种群中，数量性状之间以及性状与酶之间存在显著关联。杂交种群中的表型方差也会增加。这些观察结果可以通过潜在位点之间的连锁不平衡来解释。然而，性状之间协方差的平均大小约为酶位点之间连锁不平衡预期值的一半。这种差异不容易通过非加性基因作用来解释。这个难题目前尚未解决，需要进一步研究。
