Data from: Invasive Bromus tectorum alters natural selection in arid systems

While much research has documented the impact of invaders on native communities and ecosystem services, there has been less work quantifying how invasion affects the genetic composition of native populations. That is, when invaders dominate a community, can they shift selection regimes and impact the evolutionary trajectory of native populations?
The invasion of the annual grass Bromus tectorum in the Intermountain West provides an opportunity to quantify the effects of invasion on natural selection in wild populations. The shift from a perennial-dominated native community to one dominated by a highly competitive annual species alters the timing and intensity of competitive pressure, which has the potential to strongly shift selection regimes for native plants.
To quantify traits under selection in contrasting environments, we planted seeds of two native perennial grasses, Elymus multisetus and Poa secunda, into three invaded, invaded but weeded and relatively uninvaded sagebrush systems. We quantified phenotypic traits of seedlings from separate maternal plants, describing differences in phenotypes among individuals. We then asked which traits were associated with survival and plant size in adjacent invaded and uninvaded sagebrush systems, following individual seed performance for 3 years.
We found evidence for divergent selection between invaded and uninvaded sagebrush systems, with contrasting phenotypic traits associated with greater survival or plant size in these different growing conditions at all three field sites. For example, at one field site, P. secunda families with higher root tip production were more likely to survive in invaded and weeded environments, but this was not the case in uninvaded environments. Similarly, for E. multisetus, root mass fraction, seed mass and allocation to coarse or fine roots affected survival and plant size, again with contrasting relationships across invaded, weeded or uninvaded environments.
Synthesis. Impacts of invasive species extend beyond ecosystem and community composition changes and can affect the evolutionary trajectory of native populations. By quantifying natural selection in invaded landscapes, we identified phenotypic traits that are potentially adaptive in these invaded systems. Importantly, these traits differed from traits associated with success in uninvaded communities. This insight into adaptive, contemporary evolution in native species can guide restoration and conservation efforts.

已有大量研究阐明了入侵物种对本地群落及生态系统服务的影响，但针对入侵如何改变本地种群遗传组成的定量研究仍相对匮乏。简言之，当入侵物种主导某一群落时，它们能否改变自然选择模式，并进而影响本地种群的进化轨迹？
一年生草本植物旱雀麦（Bromus tectorum）在美国西部山间地区的入侵，为定量研究入侵对野生种群自然选择的影响提供了理想契机。原本以多年生植物占优的本地群落，被竞争力极强的一年生物种取代后，竞争压力的发生时机与强度均发生改变，这极有可能显著重塑本地植物的自然选择模式。
为定量对比不同环境下受选择的表型性状，我们将两种本地多年生草本——多穗披碱草（Elymus multisetus）和细茎早熟禾（Poa secunda）的种子，分别种植于三类蒿属灌丛生境：已入侵生境、去除入侵植物的入侵生境，以及相对未受入侵的生境。我们对来自不同母本植株的幼苗进行表型性状定量分析，以描述个体间的表型差异。随后，我们对单粒种子的存活情况进行了长达3年的跟踪，以探究在相邻的入侵与未入侵蒿属灌丛生境中，哪些性状与幼苗存活率及植株尺寸显著相关。
我们在三类野外样地中均发现，入侵与未入侵的蒿属灌丛生境间存在歧化选择：在这两种生长环境中，与更高存活率及更大植株尺寸相关的表型性状存在显著差异。例如，在其中一处样地，细茎早熟禾（Poa secunda）的家系若根尖产量更高，在入侵及去除入侵的生境中存活率也更高，但这一规律在未入侵生境中并不成立。类似地，多穗披碱草（Elymus multisetus）的根质量分数、种子质量以及粗/细根分配比例，均会影响其存活率与植株尺寸，且在入侵、去除入侵及未入侵生境中呈现出截然不同的相关关系。
研究总结：入侵物种的影响不仅局限于生态系统与群落组成的改变，还能够作用于本地种群的进化轨迹。通过定量研究入侵生境中的自然选择过程，我们鉴定出了在入侵生境中可能具有适应性的表型性状。值得注意的是，这些性状与未入侵生境中利于物种成功定植的性状存在显著差异。针对本地物种适应性当代进化的这一认知，可为生态修复与保护工作提供重要指导。