School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK.
CIDE-CSIC, Montcada, Valencia, Spain.
Proc Biol Sci. 2023 Apr 26;290(1997):20230141. doi: 10.1098/rspb.2023.0141.
The vast variation in floral traits across angiosperms is often interpreted as the result of adaptation to pollinators. However, studies in wild populations often find no evidence of pollinator-mediated selection on flowers. Evolutionary theory predicts this could be the outcome of periods of stasis under stable conditions, followed by shorter periods of pollinator change that provide selection for innovative phenotypes. We asked if periods of stasis are caused by stabilizing selection, absence of other forms of selection or by low trait ability to respond even if selection is present. We studied a plant predominantly pollinated by one bee species across its range. We measured heritability and evolvability of traits, using genome-wide relatedness in a large wild population, and combined this with estimates of selection on the same individuals. We found evidence for both stabilizing selection and low trait heritability as potential explanations for stasis in flowers. The area of the standard petal is under stabilizing selection, but the variability is not heritable. A separate trait, floral weight, presents high heritability, but is not currently under selection. We show how a simple pollination environment coincides with the absence of current prerequisites for adaptive evolutionary change, while heritable variation remains to respond to future selection pressures.
被子植物的花部性状在种间存在广泛变异，通常被解释为对传粉者适应的结果。然而，在野生种群中的研究往往没有发现花部性状受到传粉者介导选择的证据。进化理论预测，这可能是在稳定条件下处于稳定状态的结果，随后是较短的传粉者变化时期，为创新表型提供选择。我们想知道稳定状态是否是由稳定选择、其他形式的选择缺失或低性状响应能力引起的，即使存在选择。我们研究了一种主要由一种蜜蜂物种授粉的植物，在其分布范围内测量了性状的遗传力和可进化性，使用大量野生个体的全基因组亲缘关系进行了测量，并结合了对同一个体的选择估计。我们发现稳定选择和低性状遗传力都有可能是花部稳定的原因。标准花瓣的面积受到稳定选择的限制，但这种变异性是不可遗传的。另一个单独的特征，花的重量，表现出高遗传力，但目前不受选择的影响。我们展示了简单的授粉环境如何与适应性进化变化的当前先决条件的缺失相一致，而遗传变异仍然可以应对未来的选择压力。
