Mezey Jason G, Houle David
Department of Biological Science, Florida State University, Tallahassee, Florida 32306-1100, USA.
Evolution. 2005 May;59(5):1027-38.
Absolute constraints are limitations on genetic variation that preclude evolutionary change in some aspect of the phenotype. Absolute constraints may reflect complete absence of variation, lack of genetic variation that extends the range of phenotypes beyond some limit, or lack of additive genetic variation. This last type of absolute constraint is bidirectional, because the mean cannot evolve to be larger or smaller. Most traits do possess genetic variation, so bidirectional absolute constraints are most likely to be detected in a multivariate context, where they would reflect combinations of traits, or dimensions in phenotype space that cannot evolve. A bidirectional absolute constraint will cause the additive genetic covariance matrix (G) to have a rank less than the number of traits studied. In this study, we estimate the rank of the G-matrix for 20 aspects of wing shape in Drosophila melanogaster. Our best estimates of matrix rank are 20 in both sexes. Lower 95% confidence intervals of rank are 17 for females and 18 for males. We therefore find little evidence of bidirectional absolute constraints. We discuss the importance of this result for resolving the relative roles of selection and drift processes versus constraints in the evolution of wing shape in Drosophila.
绝对限制是对遗传变异的限制，它排除了表型某些方面的进化变化。绝对限制可能反映出变异的完全缺失、缺乏能将表型范围扩展到某个限度之外的遗传变异，或者缺乏加性遗传变异。最后这种类型的绝对限制是双向的，因为均值既不能进化得更大也不能更小。大多数性状确实存在遗传变异，所以双向绝对限制最有可能在多变量背景下被检测到，在这种情况下它们会反映性状的组合，或者表型空间中无法进化的维度。双向绝对限制会导致加性遗传协方差矩阵（G）的秩小于所研究性状的数量。在本研究中，我们估计了黑腹果蝇翅膀形状20个方面的G矩阵的秩。我们对矩阵秩的最佳估计在两性中都是20。秩的95%置信区间下限，雌性为17，雄性为18。因此，我们几乎没有发现双向绝对限制的证据。我们讨论了这一结果对于解决选择和漂变过程与限制在果蝇翅膀形状进化中的相对作用的重要性。
