Barrett Spencer C H, Shore Joel S
Department of Botany, University of Toronto, Toronto, Ontario, M5S 1A1, Canada.
Evolution. 1987 Mar;41(2):340-354. doi: 10.1111/j.1558-5646.1987.tb05802.x.
The evolutionary and functional relationships among breeding systems and floral morphology were investigated in the Turnera ulmifolia complex. Predictions of a model of breeding system evolution among distylous and homostylous varieties were tested. Chromosome counts of 73 accessions revealed an association between breeding system and chromosome number. Diploid and tetraploid populations of five taxonomic varieties are distylous and self-incompatible, whereas hexaploid populations of three varieties are homostylous and self-compatible. The latter occur at different margins of the geographical range of the complex. Crossing studies and analyses of pollen and ovule fertility in F 's revealed that the three homostylous varieties are intersterile. To test the prediction that, homostylous varieties are long homostyles that have originated by crossing over within the distyly supergene, a crossing program was undertaken among distylous and homostylous plants. Residual incompatibility was observed in styles and pollen of each homostylous variety with patterns consistent with predictions of the cross-over model. The intersterility of hexaploid varieties suggests that long homostyly has arisen on at least three occasions in the complex by recombination within the supergene controlling distyly. Deviation from expected compatibility behavior occurs in populations of var. angustifolia that have the longest styles. These phenotypes displayed the greatest separation between anthers and stigmas (herkogamy) and set little seed in crosses with long- or short-styled plants. This suggests that they are derived from long homostyles with shorter length styles. It is proposed that selection for increased outcrossing has favored the evolution of herkogamy in long homostyles. Estimates of outcrossing rate in a distylous population using allozyme markers confirmed that dimorphic incompatibility enforces complete outcrossing. Significant genetic variation for floral traits likely to influence the mating system, such as stigma-anther separation, occurs within and among homostylous populations of var. angustifolia on Jamaica. Estimates of the mating system of families from a population with varying degrees of stigma-anther separation, using five isozyme loci, were heterogeneous and ranged from t = 0.04-0.79. Families exhibiting the largest mean stigma-anther separation have higher outcrossing rates than those with little separation.
在榆叶马鞭草复合体中研究了繁育系统与花形态之间的进化及功能关系。对二型花柱和同型花柱变种间繁育系统进化模型的预测进行了检验。对73份材料的染色体计数揭示了繁育系统与染色体数之间的关联。五个分类变种的二倍体和四倍体种群是二型花柱且自交不亲和，而三个变种的六倍体种群是同型花柱且自交亲和。后者出现在该复合体地理分布范围的不同边缘。杂交研究以及对F1代花粉和胚珠育性的分析表明，这三个同型花柱变种是互不育的。为了检验同型花柱变种是通过二型花柱超基因内的交叉互换产生的长同型花柱这一预测，在二型花柱和同型花柱植株间开展了杂交计划。在每个同型花柱变种的花柱和花粉中观察到残余不亲和现象，其模式与交叉互换模型的预测一致。六倍体变种的互不育表明，在控制二型花柱的超基因内通过重组，长同型花柱在该复合体中至少出现了三次。在叶变窄变种的种群中出现了与预期亲和行为的偏差，该变种具有最长的花柱。这些表型在花药和柱头之间表现出最大的分离（雌雄异位），并且在与长花柱或短花柱植株杂交时结籽很少。这表明它们源自具有较短花柱的长同型花柱。有人提出，对增加异交的选择有利于长同型花柱中雌雄异位的进化。使用等位酶标记对一个二型花柱种群的异交率估计证实，二型不亲和强制完全异交。在牙买加叶变窄变种的同型花柱种群内及种群间，存在可能影响交配系统的花部性状的显著遗传变异，如柱头 - 花药分离。利用五个同工酶位点，对一个具有不同程度柱头 - 花药分离的种群中各家族的交配系统估计是异质的，范围为t = 0.04 - 0.79。平均柱头 - 花药分离最大的家族比分离小的家族具有更高的异交率。
