Departmento de Biología Vegetal y Ecología, Universidad de Sevilla, Apartado 1095, E-41080 Sevilla, Spain.
Pyrenean Institute of Ecology (CSIC), Avenida Montañana 1005, 50059 Zaragoza, Spain.
Ann Bot. 2021 Apr 17;127(5):655-668. doi: 10.1093/aob/mcab004.
Traditionally, local adaptation has been seen as the outcome of a long evolutionary history, particularly with regard to sexual lineages. By contrast, phenotypic plasticity has been thought to be most important during the initial stages of population establishment and in asexual species. We evaluated the roles of adaptive evolution and phenotypic plasticity in the invasive success of two closely related species of invasive monkeyflowers (Mimulus) in the UK that have contrasting reproductive strategies: M. guttatus combines sexual (seeds) and asexual (clonal growth) reproduction while M. × robertsii is entirely asexual.
We compared the clonality (number of stolons), floral and vegetative phenotype, and phenotypic plasticity of native (M. guttatus) and invasive (M. guttatus and M. × robertsii) populations grown in controlled environment chambers under the environmental conditions at each latitudinal extreme of the UK. The goal was to discern the roles of temperature and photoperiod on the expression of phenotypic traits. Next, we tested the existence of local adaptation in the two species within the invasive range with a reciprocal transplant experiment at two field sites in the latitudinal extremes of the UK, and analysed which phenotypic traits underlie potential local fitness advantages in each species.
Populations of M. guttatus in the UK showed local adaptation through sexual function (fruit production), while M. × robertsii showed local adaptation via asexual function (stolon production). Phenotypic selection analyses revealed that different traits are associated with fitness in each species. Invasive and native populations of M. guttatus had similar phenotypic plasticity and clonality. M. × robertsii presents greater plasticity and clonality than native M. guttatus, but most populations have restricted clonality under the warm conditions of the south of the UK.
This study provides experimental evidence of local adaptation in a strictly asexual invasive species with high clonality and phenotypic plasticity. This indicates that even asexual taxa can rapidly (<200 years) adapt to novel environmental conditions in which alternative strategies may not ensure the persistence of populations.
传统上，局部适应被视为长期进化历史的结果，特别是对于有性谱系。相比之下，表型可塑性被认为在种群建立的初始阶段和无性物种中最为重要。我们评估了适应性进化和表型可塑性在英国两种密切相关的入侵性猴面花（Mimulus）物种入侵成功中的作用，这两种物种具有不同的繁殖策略：M. guttatus 结合了有性（种子）和无性（克隆生长）繁殖，而 M. × robertsii 则完全是无性的。
我们比较了在英国纬度极端环境条件下生长的控制环境室中本地（M. guttatus）和入侵（M. guttatus 和 M. × robertsii）种群的克隆性（匍匐茎数）、花和营养表型以及表型可塑性。目标是辨别温度和光周期对表型特征表达的作用。接下来，我们在英国纬度极端的两个野外地点进行了两个物种的互惠移植实验，以检验它们在入侵范围内是否存在局部适应，并分析了每个物种潜在的局部适应优势所基于的表型特征。
英国的 M. guttatus 种群通过有性功能（果实生产）表现出局部适应，而 M. × robertsii 则通过无性功能（匍匐茎生产）表现出局部适应。表型选择分析表明，不同的特征与每个物种的适应性相关。入侵和本地 M. guttatus 种群具有相似的表型可塑性和克隆性。M. × robertsii 比本地 M. guttatus 具有更大的可塑性和克隆性，但大多数种群在英国南部温暖的条件下克隆性受到限制。
本研究提供了实验证据，证明具有高克隆性和表型可塑性的严格无性入侵物种存在局部适应。这表明，即使是无性类群也可以在新的环境条件下迅速（<200 年）适应，而替代策略可能无法确保种群的持续存在。
