Armbruster W Scott, Hansen Thomas F, Pélabon Christophe, Pérez-Barrales Rocío, Maad Johanne
University of Portsmouth, UK.
Ann Bot. 2009 Jun;103(9):1529-45. doi: 10.1093/aob/mcp095. Epub 2009 May 8.
From Darwin's time onward, biologists have thought about adaptation as evolution toward optimal trait values, but they have not usually assessed the relative importance of the distinct causes of deviations from optima. This problem is investigated here by measuring adaptive inaccuracy (phenotypic deviation from the optimum), using flower pollination as an adaptive system.
Adaptive accuracy is shown to have at least three distinct components, two of which are optimality (deviation of the mean from the optimum) and precision (trait variance). We then describe adaptive accuracy of both individuals and populations. Individual inaccuracy comprises the deviation of the genotypic target (the mean phenotype of a genotype grown in a range of environments) from the optimum and the phenotypic variation around that genotypic target (phenotypic imprecision). Population inaccuracy has three basic components: deviation of the population mean from the optimum, variance in the genotypic targets and phenotypic imprecision. In addition, a fourth component is proposed, namely within-population variation in the optimum. These components are directly estimable, have additive relationships, and allow exploration of the causes of adaptive inaccuracy of both individuals and populations. Adaptive accuracy of a sample of flowers is estimated, relating floral phenotypes controlling pollen deposition on pollinators to adaptive optima defined as the site most likely to get pollen onto stigmas (male inaccuracy). Female inaccuracy is defined as the deviation of the position of stigma contact from the expected location of pollen on pollinators.
A surprising amount of variation in estimated accuracy within and among similar species is found. Some of this variation is generated by developmental changes in positions of stigmas or anthers during anthesis (the floral receptive period), which can cause dramatic change in accuracy estimates. There seem to be trends for higher precision and accuracy in flowers with higher levels of integration and dichogamy (temporal separation of sexual functions), and in those that have pollinators that are immobile (or immobilized) during pollen transfer. Large deviations from putative adaptive optima were observed, and these may be related to the effects of conflicting selective pressures on flowers, such as selection against self-pollination promoting herkogamy (spatial separation of pollen and stigmas).
Adaptive accuracy is a useful concept for understanding the adaptive significance of phenotypic means and variances of floral morphology within and among populations and species. Estimating and comparing the various components of adaptive accuracy can be particularly helpful for identifying the causes of inaccuracy, such as conflicting selective pressures, low environmental canalization and developmental instability.
从达尔文时代起，生物学家就将适应视为朝着最优性状值的进化，但他们通常并未评估偏离最优值的不同原因的相对重要性。本文以花朵授粉作为一个适应系统，通过测量适应性不精确性（表型与最优值的偏差）来研究这一问题。
适应性精确性至少有三个不同的组成部分，其中两个是最优性（均值与最优值的偏差）和精确性（性状方差）。然后我们描述了个体和种群的适应性精确性。个体不精确性包括基因型目标（在一系列环境中生长的基因型的平均表型）与最优值的偏差以及该基因型目标周围的表型变异（表型不精确性）。种群不精确性有三个基本组成部分：种群均值与最优值的偏差、基因型目标的方差和表型不精确性。此外，还提出了第四个组成部分，即种群内最优值的变异。这些组成部分可以直接估计，具有加性关系，并允许探索个体和种群适应性不精确性的原因。估计了一组花朵样本的适应性精确性，将控制传粉者上花粉沉积的花表型与定义为最有可能使花粉落到柱头上的位置的适应性最优值相关联（雄性不精确性）。雌性不精确性定义为柱头接触位置与传粉者上花粉预期位置的偏差。
在相似物种内部和之间，估计的精确性存在惊人数量的变异。其中一些变异是由花期（花的接受期）期间柱头或花药位置的发育变化产生的，这可能导致精确性估计值发生巨大变化。在具有更高整合度和雌雄异熟（性功能的时间分离）的花朵中，以及在花粉转移期间传粉者不动（或被固定）的花朵中，似乎存在更高精确性和准确性的趋势。观察到与假定的适应性最优值有很大偏差，这些偏差可能与对花朵的相互冲突的选择压力的影响有关，例如反对自花授粉促进雌雄异位（花粉和柱头的空间分离）的选择。
适应性精确性是一个有用的概念，有助于理解种群和物种内部及之间花形态的表型均值和方差的适应意义。估计和比较适应性精确性的各个组成部分对于识别不精确性的原因可能特别有帮助，例如相互冲突的选择压力、低环境稳定性和发育不稳定性。
