Wilkinson Gerald S, Fowler Kevin, Partridge Linda
Department of Zoology, University of Maryland, College Park, MD, 20742, USA.
Department of Zoology, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, SCOTLAND.
Evolution. 1990 Dec;44(8):1990-2003. doi: 10.1111/j.1558-5646.1990.tb04305.x.
The genetic covariance and correlation matrices for five morphological traits were estimated from four populations of fruit flies, Drosophila melanogaster, to measure the extent of change in genetic covariances as a result of directional selection. Two of the populations were derived from lines that had undergone selection for large or small thorax length over the preceding 23 generations. A third population was constituted using flies from control lines that were maintained with equivalent population sizes as the selected lines. The fourth population contained flies from the original cage population from which the selected and control lines had been started. Tests of the homogeneity of covariance matrices using maximum likelihood techniques revealed significant changes in covariance structure among the selected lines. Prediction of base population trait means from selected line means under the assumption of constant genetic covariances indicated that genetic covariances for the small population differed more from the base population than did the covariances for the large population. The predicted small population means diverged farther from the expected means because the additive genetic variance associated with several traits increased in value and most of the genetic covariances associated with one trait changed in sign. These results illustrate that genetic covariances may remain nearly constant in some situations while changing markedly in others. Possible developmental reasons for the genetic changes are discussed.
从黑腹果蝇的四个种群中估计了五个形态性状的遗传协方差和相关矩阵，以衡量定向选择导致的遗传协方差变化程度。其中两个种群来自在过去23代中对大或小胸长进行过选择的品系。第三个种群由来自对照品系的果蝇组成，这些对照品系的种群大小与选择品系相当。第四个种群包含来自原始笼养种群的果蝇，所选品系和对照品系均由此开始。使用最大似然技术对协方差矩阵的齐次性进行检验，结果显示所选品系之间的协方差结构有显著变化。在遗传协方差恒定的假设下，根据所选品系的均值预测基础种群性状均值，结果表明，小种群的遗传协方差与基础种群的差异比大种群的协方差与基础种群的差异更大。预测的小种群均值与预期均值的偏差更大，因为与几个性状相关的加性遗传方差值增加，并且与一个性状相关的大多数遗传协方差符号发生了变化。这些结果表明，遗传协方差在某些情况下可能几乎保持不变，而在其他情况下则会发生显著变化。文中讨论了遗传变化可能的发育原因。
