Comes Hans Peter, Abbott Richard J
School of Environmental and Evolutionary Biology, University of St. Andrews, St. Andrews, Fife, KY16 9TH, United Kingdom.
Evolution. 1999 Feb;53(1):36-54. doi: 10.1111/j.1558-5646.1999.tb05331.x.
To shed light on the potential effects of xeric/arid versus mesic environments on plant population genetic structure and patterns of gene flow, we have compared allozyme and cpDNA haplotype variation in populations of two closely related, highly outcrossed, and largely wind-dispersed winter annuals of Senecio (Asteraceae). The species form a distinctive zone of parapatric distribution in the Near East by differing in their ecogeographical regimes. Senecio vernalis mainly thrives in the mesic Mediterranean life zone of Israel, whereas S. glaucus inhabits either xeric maritime or arid (semi-) desert sites. Significant differences in allozymic population subdivision among S. vernalis (θ = 0.04; Nm = 5.85) and S. glaucus (θ = 0.12; Nm = 1.85) largely resulted from topogeographical substructuring present within the latter species. Because of the similarity of within-region estimates of population structure for S. glaucus with those measured among populations of S. vernalis, it appears unlikely that ecological "aridity" factors per se are important in influencing levels of population differentiation in these species. Based on hierarchical F-statistics and tests of isolation by distance, we further conclude that geographical topologies influence the level and mode of nuclear gene flow (via pollen and/or seed) among and within subsets of S. glaucus populations, although without providing a complete barrier to interregional dispersal (dNm = 2.16) and without promoting allopatric differentiation via drift. The allozymic data further suggested that S. vernalis and S. glaucus form a zone of secondary contact in the Near East, accompanied by an almost complete interspecific barrier to nuclear gene flow (dnNm = 0.253). However, to account for the considerable sharing of cpDNA haplotypes, both at the intra- and interspecific level, it is necessary to invoke either (1) selection acting against alien nuclear but not cytoplasmic DNA; or (2) the sporadic immigration of cpDNA via seed with large homogenizing effects on cytoplasmic population structure over time.
为了阐明干旱/干旱环境与湿润环境对植物种群遗传结构和基因流动模式的潜在影响，我们比较了千里光属（菊科）两种亲缘关系密切、高度异交且主要靠风传播的冬季一年生植物种群中的等位酶和叶绿体DNA单倍型变异。这两个物种在近东地区通过不同的生态地理格局形成了一个独特的邻域分布带。春千里光主要生长在以色列湿润的地中海生物区，而灰叶千里光则栖息在干旱的沿海或干旱（半）沙漠地区。春千里光（θ = 0.04；Nm = 5.85）和灰叶千里光（θ = 0.12；Nm = 1.85）在等位酶种群细分上的显著差异主要源于后者物种内部存在的地形地理亚结构。由于灰叶千里光区域内种群结构的估计值与春千里光种群间测量值相似，生态“干旱”因素本身似乎不太可能对这些物种的种群分化水平产生重要影响。基于层次F统计量和距离隔离检验，我们进一步得出结论，地理拓扑结构影响灰叶千里光种群子集间和子集内核基因流动（通过花粉和/或种子）的水平和模式，尽管没有对区域间扩散形成完全障碍（dNm = 2.16），也没有通过漂变促进异域分化。等位酶数据进一步表明，春千里光和灰叶千里光在近东地区形成了一个二次接触带，伴随着几乎完全的种间核基因流动障碍（dnNm = 0.253）。然而，为了解释在种内和种间水平上叶绿体DNA单倍型的大量共享，有必要要么（1）选择作用于外来核DNA而非细胞质DNA；要么（2）叶绿体DNA通过种子的零星迁入，随着时间的推移对细胞质种群结构产生巨大的同质化影响。
