Departamento de Biología y Geología, Universidad Rey Juan Carlos, Madrid, Spain.
PLoS One. 2012;7(9):e44955. doi: 10.1371/journal.pone.0044955. Epub 2012 Sep 19.
The ability to succeed in diverse conditions is a key factor allowing introduced species to successfully invade and spread across new areas. Two non-exclusive factors have been suggested to promote this ability: adaptive phenotypic plasticity of individuals, and the evolution of locally adapted populations in the new range. We investigated these individual and population-level factors in Polygonum cespitosum, an Asian annual that has recently become invasive in northeastern North America. We characterized individual fitness, life-history, and functional plasticity in response to two contrasting glasshouse habitat treatments (full sun/dry soil and understory shade/moist soil) in 165 genotypes sampled from nine geographically separate populations representing the range of light and soil moisture conditions the species inhabits in this region. Polygonum cespitosum genotypes from these introduced-range populations expressed broadly similar plasticity patterns. In response to full sun, dry conditions, genotypes from all populations increased photosynthetic rate, water use efficiency, and allocation to root tissues, dramatically increasing reproductive fitness compared to phenotypes expressed in simulated understory shade. Although there were subtle among-population differences in mean trait values as well as in the slope of plastic responses, these population differences did not reflect local adaptation to environmental conditions measured at the population sites of origin. Instead, certain populations expressed higher fitness in both glasshouse habitat treatments. We also compared the introduced-range populations to a single population from the native Asian range, and found that the native population had delayed phenology, limited functional plasticity, and lower fitness in both experimental environments compared with the introduced-range populations. Our results indicate that the future spread of P. cespitosum in its introduced range will likely be fueled by populations consisting of individuals able to express high fitness across diverse light and moisture conditions, rather than by the evolution of locally specialized populations.
在不同条件下取得成功的能力是引入物种成功入侵和扩散到新区域的关键因素。有两个非排他性因素被认为可以促进这种能力：个体的适应性表型可塑性，以及新范围内局部适应种群的进化。我们研究了这些个体和种群水平的因素，以探讨亚洲一年生植物节节草（Polygonum cespitosum）在最近入侵北美的东北部分地区的情况。我们从代表该物种在该地区栖息的光照和土壤水分条件范围的九个地理上分离的种群中，对 165 个基因型进行了个体适应性、生活史和功能可塑性的特征描述。来自这些引入种范围种群的节节草基因型表现出广泛相似的可塑性模式。在全阳光、干燥条件下，来自所有种群的基因型都增加了光合速率、水分利用效率和对根组织的分配，与模拟林下条件下表达的表型相比，繁殖适应性显著提高。尽管存在种群间平均性状值和塑性响应斜率的细微差异，但这些种群差异并没有反映出在种群起源地测量的环境条件下的局部适应性。相反，某些种群在两种温室生境处理中都表现出更高的适应性。我们还将引入种范围的种群与来自亚洲原生种范围的单个种群进行了比较，发现与引入种范围的种群相比，原生种群的物候期延迟、功能可塑性有限、适应性较低，在两种实验环境下均如此。我们的研究结果表明，节节草在其引入种范围的未来传播将可能受到具有广泛适应不同光照和水分条件的高适应性个体的种群所驱动，而不是由局部特化种群的进化所驱动。
