Weller Stephen G, Sakai Ann K, Straub Christina
Department of Ecology and Evolutionary Biology, University of California, Irvine, California, 92717.
Evolution. 1996 Feb;50(1):23-34. doi: 10.1111/j.1558-5646.1996.tb04469.x.
Genetic diversity of allozymes, genetic identity based on allozyme variability, and phylogenetic relationships were studied with respect to breeding system diversity, population size, and island age in 20 of the 29 species of Schiedea and Alsinidendron (Caryophyllaceae: Alsinoideae), a monophyletic lineage endemic to the Hawaiian Islands. Average levels of genetic variability in Schiedea and Alsinidendron were comparable to or higher than those found in other Hawaiian lineages for which equivalent data are available [Bidens, Tetramolopium, and the silversword alliance (Asteraceae: Madiinae)] and similar to average values for species of dicots. Allozyme variability was strongly dependent on breeding system, which varies widely in the Hawaiian Alsinoideae. Species with autogamous breeding systems showed very low variability, measured as the number of alleles per locus, percent polymorphic loci, and mean heterozygosity per locus. Outcrossing hermaphroditic and dimorphic species (those with gynodioecious, subdioecious, and dioecious breeding systems) showed significantly higher genetic variability. Small population size was associated with lower values for all measures of genetic variability. Nearly half of the species occurring in small populations are also autogamous; thus, both factors may have influenced levels of genetic variability in these species. Founder effect was apparent in one species (Schiedea adamantis), which occurs in a single large population, has a gynodioecious breeding system but a very low genetic variability. Island age appeared to have little effect on genetic variability. Slightly lower values of genetic variability for species occurring on Kaua'i and O'ahu result primarily from the occurrence of autogamous Alsinidendron species on those islands. Values for Nei's genetic identity for different species pairs were 0.201-0.942, a far greater range than in Bidens, the silversword alliance, and Tetramolopium. Using UPGMA clustering, there was only moderate support for relationships detected through cladistic analysis. Nei's unbiased genetic identity (I) was greatest among species with outcrossing breeding systems, which for the most part clustered together. Nei's genetic identities for self-fertilizing species were low, indicating that these species are less similar to one another and to outcrossing species, regardless of their affinities based on cladistic analysis. Parsimony analysis of allele frequency data supported two clades also found in phylogenetic analyses using morphological and molecular data. Clades recognized in parsimony analysis of allele frequencies were those lineages containing selfing species, indicating that conditions favoring fixation of alleles occurred in ancestral species. In contrast, maintenance of high genetic diversity in outcrossing species interferes with recognition of phylogenetic relationships using allozyme variability.
在夏威夷群岛特有的一个单系类群——Schiedea和Alsinidendron（石竹科：繁缕亚科）的29个物种中的20个物种里，研究了等位酶的遗传多样性、基于等位酶变异性的遗传同一性以及系统发育关系，涉及繁殖系统多样性、种群大小和岛屿年龄。Schiedea和Alsinidendron的平均遗传变异水平与其他有等效数据的夏威夷类群[鬼针草属、四棱果属和银剑联盟（菊科：千里光亚族）]相当或更高，并且与双子叶植物物种的平均值相似。等位酶变异性强烈依赖于繁殖系统，而夏威夷繁缕亚科的繁殖系统差异很大。具有自花授粉繁殖系统的物种表现出非常低的变异性，通过每个位点的等位基因数量、多态位点百分比和每个位点的平均杂合度来衡量。异交雌雄同体和二态物种（具有雌全异株、亚雌雄异株和雌雄异株繁殖系统的物种）表现出显著更高的遗传变异性。小种群大小与所有遗传变异度量值较低相关。在小种群中出现的近一半物种也是自花授粉的；因此，这两个因素可能都影响了这些物种的遗传变异水平。奠基者效应在一个物种（亚当斯Schiedea）中很明显，该物种出现在一个单一的大种群中，具有雌全异株繁殖系统，但遗传变异性非常低。岛屿年龄似乎对遗传变异性影响很小。考艾岛和瓦胡岛上出现的物种的遗传变异值略低，主要是因为这些岛屿上存在自花授粉的Alsinidendron物种。不同物种对的内氏遗传同一性值为0.201 - 0.942，范围远比鬼针草属、银剑联盟和四棱果属大。使用UPGMA聚类，对通过分支分析检测到的关系只有适度的支持。内氏无偏遗传同一性（I）在具有异交繁殖系统的物种中最大，这些物种在很大程度上聚集在一起。自花受精物种的内氏遗传同一性较低，这表明这些物种彼此之间以及与异交物种的相似性较低，无论基于分支分析它们的亲缘关系如何。等位基因频率数据的简约分析支持了在使用形态学和分子数据的系统发育分析中也发现的两个分支。在等位基因频率的简约分析中识别出的分支是那些包含自交物种的谱系，这表明有利于等位基因固定的条件发生在祖先物种中。相比之下，异交物种中高遗传多样性的维持干扰了使用等位酶变异性来识别系统发育关系。
