Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystems, College of the Environment and Ecology, Xiamen University, Fujian, 361102, China.
Section of Evolution and Ecology, University of California, Davis, California, 95616, USA.
Ecology. 2017 Jun;98(6):1591-1599. doi: 10.1002/ecy.1815. Epub 2017 May 15.
Ecological invasions are facilitated by pre-adaptation and phenotypic plasticity, upon which evolution can act. The rapid invasion of the intertidal grass Spartina alterniflora in China during the last 36 yr is a test case for the roles of these mechanisms. A previous study of S. alterniflora in China found strong latitudinal clines in vegetative and sexual traits and concluded that most of this variation was due to phenotypic plasticity. Recent observations suggested provenance-by-environment interactions, and we employed common gardens at multiple latitudes as a test of this idea. Phenotypically, field plant height, which correlates strongly with biomass and other indices of vegetative performance in this species, showed a hump-shaped relationship across 10 sites, covering 19° of latitude; field seed set increased linearly with latitude. To assess the role of plasticity vs. genetic differentiation in these patterns, we grew plants from the ten field sites in three common gardens at low (20.9° N), mid (28.3° N), and high (38.0° N) latitudes to maturity, at 18 months. Plant height varied among common gardens, with the tallest plants at mid latitude, mirroring the field pattern, consistent with the previous study. Within the gardens, latitude of origin also affected plant height. Seed set varied among the gardens, with the greatest values at high latitudes, again mirroring the field pattern and indicating substantial plasticity. Evidence of evolution was found as increasing seed set with latitude among provenances within common gardens. However, the effect differed among common gardens, with the greatest slope in the high-latitude garden, lower slope in the mid-latitude garden, and no relationship in the low-latitude garden, indicating a provenance-by-environment interaction. The number of surviving plants also suggested a provenance-by-environment interaction; no relationship with latitude among provenances in the two southern gardens and increasing survival with latitude in the northern garden. Field seedling density was ~200-fold greater at high than at low latitude sites. The profuse seed germination and recruitment in the north could have created high selection intensity resulting in evolution of reproductive traits at high latitudes with the result that the mechanisms of the invasion differ with latitude.
生态入侵是由预适应和表型可塑性促成的，而进化可以作用于这些机制。在中国，互花米草在过去 36 年中的快速入侵就是这些机制作用的一个例证。先前对中国互花米草的研究发现，其在营养繁殖和有性繁殖方面存在强烈的纬度梯度，并且认为这种变化主要是由表型可塑性引起的。最近的观察结果表明，存在起源地-环境互作，我们在多个纬度的共同园中进行了测试。表型上，野外植物高度与该物种的生物量和其他营养繁殖性能指标密切相关，在跨越 19 个纬度的 10 个地点上呈现出驼峰形关系；野外种子结实率随纬度线性增加。为了评估可塑性和遗传分化在这些模式中的作用，我们将 10 个野外地点的植物种植在低纬度（20.9°N）、中纬度（28.3°N）和高纬度（38.0°N）的三个共同园中，在 18 个月时成熟。植物高度在共同园中有所不同，中纬度的植物最高，与野外模式一致，与先前的研究一致。在园内，起源地纬度也影响植物高度。在园内，种子结实率不同，高纬度的种子结实率最高，再次与野外模式一致，表明存在大量可塑性。在共同园中，起源地的种子结实率随纬度增加，这表明存在进化证据。然而，这种效应在不同的共同园中有所不同，在高纬度的共同园中斜率最大，在中纬度的共同园中斜率较小，而在低纬度的共同园中没有关系，表明存在起源地-环境互作。幸存植物的数量也表明存在起源地-环境互作；在两个南部的共同园中，起源地之间没有与纬度相关的关系，而在北部的共同园中，幸存植物的数量随纬度增加而增加。野外幼苗密度在高纬度地点比低纬度地点高约 200 倍。北方丰富的种子萌发和繁殖可能导致选择强度增加，从而导致在高纬度地区繁殖特征的进化，其结果是入侵机制随纬度而异。
