Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, USA.
Proc Biol Sci. 2013 May 22;280(1763):20131043. doi: 10.1098/rspb.2013.1043. Print 2013 Jul 22.
An evolutionary response to selection requires genetic variation; however, even if it exists, then the genetic details of the variation can constrain adaptation. In the simplest case, unlinked loci and uncorrelated phenotypes respond directly to multivariate selection and permit unrestricted paths to adaptive peaks. By contrast, 'antagonistic' pleiotropic loci may constrain adaptation by affecting variation of many traits and limiting the direction of trait correlations to vectors that are not favoured by selection. However, certain pleiotropic configurations may improve the conditions for adaptive evolution. Here, we present evidence that the Arabidopsis thaliana gene FRI (FRIGIDA) exhibits 'adaptive' pleiotropy, producing trait correlations along an axis that results in two adaptive strategies. Derived, low expression FRI alleles confer a 'drought escape' strategy owing to fast growth, low water use efficiency and early flowering. By contrast, a dehydration avoidance strategy is conferred by the ancestral phenotype of late flowering, slow growth and efficient water use during photosynthesis. The dehydration avoidant phenotype was recovered when genotypes with null FRI alleles were transformed with functional alleles. Our findings indicate that the well-documented effects of FRI on phenology result from differences in physiology, not only a simple developmental switch.
对选择的进化反应需要遗传变异;然而,即使存在遗传变异,那么变异的遗传细节也可能限制适应。在最简单的情况下,不连锁的基因座和不相关的表型直接对多变量选择作出反应,并允许适应峰的不受限制的路径。相比之下,“拮抗”多效性基因座可能通过影响许多性状的变异并将性状相关性的方向限制为不受选择青睐的向量来限制适应。然而,某些多效性配置可能改善适应性进化的条件。在这里,我们提供的证据表明,拟南芥基因 FRI(FRIGIDA)表现出“适应性”多效性,沿着导致两种适应性策略的轴产生性状相关性。衍生的、低表达的 FRI 等位基因由于快速生长、低水分利用效率和早期开花而赋予“耐旱逃避”策略。相比之下,由晚期开花、生长缓慢和光合作用期间高效水分利用的祖先表型赋予脱水回避策略。当具有无效 FRI 等位基因的基因型转化为具有功能等位基因时,恢复了脱水回避表型。我们的研究结果表明,FRI 对物候学的有充分记录的影响源自生理学上的差异,而不仅仅是简单的发育开关。