Young J P
Genetics. 1979 Jul;92(3):953-70. doi: 10.1093/genetics/92.3.953.
Genotype frequencies and fecundities were recorded over a period of two years for three polymorphic enzyme loci (Est, Mdh and Got) in a parthenogenetic natural population of Daphnia magna Straus (Crustacea: Cladocera). There was a large excess of heterozygotes at each locus, and some nonrandom association between loci, although 29 different three-locus genotypes were detected. There were small but significant changes in genotype frequencies that did not follow any clear seasonal cycles or overall trends, and the genotypes often differed significantly in fecundity, although the direction of the difference was not constant. These fitness differences were probably not attributable to the specific loci studied.--Models of balancing selection are of two types: segregation-balanced (e.g., heterosis) and competition-balanced (e.g., frequency dependence). Only the latter type can stabilize diversity in a clonal population. The observed selection was not heterotic, but it is not certain that it was stabilizing either. Clonal competition did not lead to victory by a single, fittest clone; genotypic diversity remained high.
在为期两年的时间里，对大型溞（甲壳纲：枝角亚目）孤雌生殖自然种群中的三个多态酶位点（酯酶、苹果酸脱氢酶和谷草转氨酶）的基因型频率和繁殖力进行了记录。每个位点都存在大量杂合子过剩的情况，并且位点之间存在一些非随机关联，尽管检测到了29种不同的三位点基因型。基因型频率存在微小但显著的变化，这些变化并不遵循任何明确的季节周期或总体趋势，并且基因型在繁殖力方面通常存在显著差异，尽管差异的方向并不恒定。这些适合度差异可能并非归因于所研究的特定位点。——平衡选择模型有两种类型：分离平衡型（例如杂种优势）和竞争平衡型（例如频率依赖）。只有后一种类型能够在克隆种群中稳定多样性。观察到的选择并非杂种优势型，但也不确定它是否是稳定型。克隆竞争并未导致单一最适应克隆的胜利；基因型多样性仍然很高。
