Austen E J, Forrest J R K, Weis A E
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.
J Evol Biol. 2015 Jan;28(1):65-79. doi: 10.1111/jeb.12538. Epub 2015 Jan 6.
Variation among the leaves, flowers or fruit produced by a plant is often regarded as a nuisance to the experimenter and an impediment to selection. Here, we suggest that within-plant variation can drive selection on other plant-level traits. We examine within-plant variation in floral sex allocation and in fruit set and predict that such variation generates variation in male success among plants, thereby driving selection on flowering time. We tested this prediction in a simulation model estimating selection on flowering time through male fitness when floral sex allocation and/or fruit set vary directionally among flowers on plants. We parameterized the model through a quantitative literature survey of within-plant change in sex allocation. As predicted, within-plant variation in floral sex allocation and in fruit set probability can generate selection on flowering time through male fitness. Declining fruit set from first to last flowers on plants, as occurs in many species, selected for early flowering onset through male fitness. This result was robust to self-incompatibility and to varying returns on male versus female investment. Selection caused by declining fruit set was strong enough to reverse the selection for late flowering that can be caused by intrafloral protandry. Our model provides testable predictions regarding selection on flowering time through male fitness. The model also establishes the intriguing possibility that within-plant variation may influence selection on other traits, regardless of whether that variation is under selection itself.
植物产生的叶片、花朵或果实之间的变异通常被实验者视为一种麻烦，也是选择过程中的一个障碍。在此，我们认为植物内部的变异能够推动对其他植物水平性状的选择。我们研究了植物内部花的性别分配和坐果情况的变异，并预测这种变异会导致不同植株间雄性成功率的差异，从而推动对开花时间的选择。我们在一个模拟模型中验证了这一预测，该模型通过雄性适合度来估计当植物上的花在性别分配和/或坐果方面存在定向差异时对开花时间的选择。我们通过对植物内部性别分配变化的定量文献调查为模型设定参数。正如预测的那样，植物内部花的性别分配和坐果概率的变异能够通过雄性适合度对开花时间产生选择作用。在许多物种中，植株上从第一朵花到最后一朵花坐果率逐渐下降，这种情况通过雄性适合度选择了较早的开花起始时间。这一结果对于自交不亲和以及雄性与雌性投资的不同回报具有稳健性。坐果率下降所导致的选择作用强大到足以扭转由花内雄蕊先熟所引起的对晚开花的选择。我们的模型提供了关于通过雄性适合度对开花时间进行选择的可检验预测。该模型还提出了一个有趣的可能性，即植物内部的变异可能会影响对其他性状的选择，无论这种变异本身是否处于选择之下。
