Hovick Stephen M, McArdle Andrea, Harrison S Kent, Regnier Emilie E
Department of Evolution, Ecology and Organismal Biology The Ohio State University Columbus OH USA.
Department of Horticulture and Crop Science The Ohio State University Columbus OH USA.
Evol Appl. 2018 Mar 14;11(6):995-1009. doi: 10.1111/eva.12614. eCollection 2018 Jul.
Spatial patterns of trait variation across a species' range have implications for population success and evolutionary change potential, particularly in range-expanding and weedy species that encounter distinct selective pressures at large and small spatial scales simultaneously. We investigated intraspecific trait variation in a common garden experiment with giant ragweed (), a highly variable agricultural weed with an expanding geographic range and broad ecological amplitude. Our study included paired populations from agricultural and natural riparian habitats in each of seven regions ranging east to west from the core of the species' distribution in central Ohio to southeastern Minnesota, which is nearer the current invasion front. We observed trait variation across both large- and small-scale putative selective gradients. At large scales, giant ragweed populations from the westernmost locations were nearly four times more fecund and had a nearly 50% increase in reproductive allocation compared to populations from the core. The degree of surface texture on fruits also declined from east to west. Greater fecundity in the west represents a putative trade-off between fruit size and fruit number across the study region, although no such trade-off was found across individual plants. This pattern may effectively result in greater propagule pressure closer to the invasion front. At smaller spatial scales, plants from agricultural populations emerged later and were smaller than plants from riparian populations. However, because plants from agricultural populations allocated more biomass to reproduction, total fecundity did not differ across habitats. Our emergence data are consistent with previous observations showing delayed emergence in agricultural compared to natural populations; thus evolutionary change may be predictable as giant ragweed continues spreading into agricultural fields throughout North America. These shifts in life-history strategy apparently bear no fecundity cost, suggesting that giant ragweed's success can be attributed at least in part to its substantial adaptive potential.
物种分布范围内性状变异的空间模式对种群成功和进化变化潜力具有重要意义，特别是对于那些在大空间尺度和小空间尺度上同时面临不同选择压力的范围扩张物种和杂草物种。我们在一项针对豚草（一种高度可变的农业杂草，地理范围不断扩大且生态幅度广泛）的共同花园实验中，研究了种内性状变异。我们的研究包括来自七个区域的农业和自然河岸栖息地的配对种群，这些区域从俄亥俄州中部该物种分布的核心区域向西至明尼苏达州东南部，后者更靠近当前的入侵前沿。我们观察到了在大尺度和小尺度假定选择梯度上的性状变异。在大尺度上，最西部位置的豚草种群的繁殖力几乎是核心区域种群的四倍，繁殖分配增加了近50%。果实表面纹理的程度也从东向西下降。西部更高的繁殖力代表了整个研究区域果实大小和果实数量之间的一种假定权衡，尽管在个体植株中未发现这种权衡。这种模式可能有效地导致在更靠近入侵前沿的地方有更大的繁殖体压力。在较小的空间尺度上，来自农业种群的植株出苗较晚且比来自河岸种群的植株小。然而，由于来自农业种群的植株将更多生物量分配给繁殖，不同栖息地的总繁殖力并无差异。我们的出苗数据与之前的观察结果一致，即农业种群的出苗比自然种群延迟；因此，随着豚草继续在北美各地向农田扩散，进化变化可能是可预测的。这些生活史策略的转变显然没有繁殖力成本，这表明豚草的成功至少部分可归因于其巨大的适应潜力。
