Department of Biology, Duke University, Durham, NC 27708, USA.
Philos Trans R Soc Lond B Biol Sci. 2010 Feb 27;365(1540):567-75. doi: 10.1098/rstb.2009.0249.
Body size and development time of Manduca sexta are both determined by the same set of three developmental-physiological factors. These define a parameter space within which it is possible to analyse and explain how phenotypic change is associated with changes in the underlying factors. Body size and development time are determined by the identical set of underlying factors, so they are not independent, but because the mechanisms by which these factors produce each phenotype are different, the two phenotypes are only weakly correlated, and the correlation is context dependent. We use a mathematical model of this mechanism to explore the association between body size and development time and show that the correlation between these two life-history traits can be positive, zero or negative, depending entirely on where in parameter space a population is located, and on which of the underlying factors has a greater variation. The gradient within this parameter space predicts the unconstrained evolutionary trajectory under directional selection on each trait. Calculations of the gradients for body size and development time revealed that these are nearly orthogonal through much of the parameter space. Therefore, simultaneous directional selection on body size and development time can be neither synergistic nor antagonistic but leads to conflicting selection on the underlying developmental parameters.
烟青虫的体型大小和发育时间均由同样的三组生理发育因素决定。这些因素界定了一个参数空间，我们可以在其中分析并解释表型变化与潜在因素变化之间的关系。体型大小和发育时间由相同的潜在因素决定，所以它们不是独立的，但由于这些因素产生每种表型的机制不同，两种表型仅具有弱相关性，且相关性取决于具体情境。我们使用这个机制的数学模型来探究体型大小和发育时间之间的关联，并表明这两个生活史特征之间的相关性可以是正的、零的或负的，这完全取决于种群在参数空间中的位置，以及哪个潜在因素的变化更大。该参数空间内的梯度可预测在每个特征上进行定向选择时的无约束进化轨迹。对体型大小和发育时间的梯度计算表明，在大部分参数空间中，这些梯度几乎是正交的。因此，体型大小和发育时间的同时定向选择既不会协同也不会拮抗，而是会导致潜在发育参数之间存在冲突的选择。
