David P, Delay B, Berthou P, Jarne P
Laboratoire Génétique et Environnement, Université Montpellier II, France.
Genetics. 1995 Apr;139(4):1719-26. doi: 10.1093/genetics/139.4.1719.
Correlations between allozyme heterozygosity and fitness-related traits, especially growth, have been documented in natural populations of marine bivalves. However, no consistent pattern has been exhibited, because heterotic effects on size vary with age and individual growth parameters are generally unknown. No consensus has emerged on the genetic basis of allozyme-associated heterosis. The species studied here, Spisula ovalis, displays annual shell growth lines, which allows us to compute individual age and growth dynamics over the whole life span. Our morphological study was coupled to a protein electrophoresis study at seven polymorphic loci. While the maximum size gained is not related to heterozygosity, the age at half maximum size, t1/2, is significantly negatively correlated with heterozygosity, indicating an heterotic effect on initial growth. The correlation between heterozygosity and size is expected to vanish when age increases, due to the form of the growth function. This decreasing correlation is consistent with previous studies. We compare the relative performances of five linear models to analyze the genetic basis of heterosis. Surprisingly, the largest part of variance in t1/2 is due to additive effects, the overdominant components being much weaker. Heterosis is therefore due to general genomic effects rather than to local overdominance restricted to allozymes or small neighboring chromosomal segments. A significant dependence of individual heterotic contributions of the enzyme loci upon expected heterozygosities, rather than metabolic function, further supports the hypothesis of enzymes acting as markers. General genomic effects can hold only if allozyme heterozygosity is positively correlated with heterozygosity at fitness-related genes scattered throughout the genome. This hypothesis is supported here by heterozygosity correlations between enzymatic loci.
在海洋双壳贝类的自然种群中，已记录到等位酶杂合性与适应性相关性状（尤其是生长）之间的相关性。然而，并未呈现出一致的模式，因为对大小的杂种优势效应随年龄而变化，且个体生长参数通常未知。关于等位酶相关杂种优势的遗传基础尚未达成共识。此处研究的物种卵形薄壳蛤显示出年度贝壳生长线，这使我们能够计算整个生命周期内的个体年龄和生长动态。我们的形态学研究与在七个多态位点进行的蛋白质电泳研究相结合。虽然所达到的最大尺寸与杂合性无关，但达到最大尺寸一半时的年龄t1/2与杂合性显著负相关，表明对初始生长存在杂种优势效应。由于生长函数的形式，预计随着年龄增长，杂合性与大小之间的相关性会消失。这种相关性的降低与先前的研究一致。我们比较了五个线性模型的相对性能，以分析杂种优势的遗传基础。令人惊讶的是，t1/2中最大部分的方差归因于加性效应，超显性成分则弱得多。因此，杂种优势是由于一般基因组效应，而非局限于等位酶或小的相邻染色体片段的局部超显性。酶位点的个体杂种优势贡献对预期杂合性而非代谢功能有显著依赖性，这进一步支持了酶作为标记的假说。只有当等位酶杂合性与遍布基因组的适应性相关基因的杂合性呈正相关时，一般基因组效应才成立。此处酶位点之间的杂合性相关性支持了这一假说。
