Data from: Phenotypic plasticity in response to environmental heterogeneity contributes to fluctuating asymmetry in plants: first empirical evidence

Fluctuating asymmetry (FA) is widely used to quantify developmental instability (DI) in ecological and evolutionary studies. It has long been recognized that FA may not exclusively originate from DI for sessile organisms such as plants, because phenotypic plasticity in response to heterogeneities in the environment might also produce FA. This study provides the first empirical evidence for this hypothesis. We reasoned that solar irradiation, which is greater on the southern side than on the northern side of plants growing in the temperate zone of the northern hemisphere, would cause systematic morphological differences and asymmetry associated with the orientation of plant parts. We used geometric morphometrics to characterize the size and shape of flower parts in Iris pumila grown in a common garden. The size of floral organs was not significantly affected by orientation. Shape and particularly its asymmetric component differed significantly according to orientation for three different floral parts. Orientation accounted for 10.4% of the total shape asymmetry within flowers in the falls, for 11.4% in the standards, and for 2.2% in the style branches. This indicates that phenotypic plasticity in response to a directed environmental factor, most likely solar irradiation, contributes to FA of flowers under natural conditions. That FA partly results from phenotypic plasticity and not just from DI needs to be considered by studies of FA in plants and other sessile organisms.

波动不对称性（Fluctuating asymmetry, FA）被广泛用于量化生态学与进化研究中的发育不稳定性（developmental instability, DI）。长期以来，学界已认识到，对于植物这类固着生物（sessile organisms）而言，波动不对称性可能并非仅由发育不稳定性产生——响应环境异质性的表型可塑性（phenotypic plasticity）同样可能引发波动不对称性。本研究为这一假说提供了首个实验证据。我们推测，在北半球温带地区生长的植物，其南侧受到的太阳辐射强于北侧，这种定向环境差异会引发与植物器官朝向相关的系统性形态差异与不对称性。我们采用几何形态测量学（geometric morphometrics）方法，对同质栽培园（common garden）中栽培的矮鸢尾（Iris pumila）的花器官大小与形状进行了量化分析。结果显示，花器官的大小并未受到朝向的显著影响；但在三种不同花器官中，花的形状及其不对称成分均随朝向呈现出显著差异。其中，垂瓣（falls）内花内总形状不对称性的10.4%可由朝向解释，旗瓣（standards）内该比例为11.4%，花柱分枝（style branches）内仅为2.2%。这表明，响应定向环境因子（极有可能为太阳辐射）的表型可塑性，会在自然条件下参与促成植物花部的波动不对称性。未来针对植物及其他固着生物的波动不对称性研究，需考虑到波动不对称性可部分源自表型可塑性，而非仅由发育不稳定性产生。