Data from: Experimental test of plant defense evolution in four species using long-term rabbit exclosures

Plant defense traits have evolved over macro- and microevolutionary timescales in response to herbivores. Although a number of studies have investigated the evolutionary impacts of herbivores over short timescales, few studies have experimentally examined what defense traits most commonly evolve and whether multiple coexisting species exhibit similar evolutionary responses to herbivores. We addressed these questions using a long-term experiment at Silwood Park, England, United Kingdom, where we excluded rabbits from 38 grassland plots for <1 to 34 years. To assess the evolutionary impacts of rabbits on plant defense traits, we collected seeds from plots containing the following perennial species: Anthoxanthum odoratum L. (Poaceae), Festuca rubra L. spp. rubra (Poaceae), Holcus lanatus L. (Poaceae), and Stellaria graminea L. (Caryophyllaceae). We then grew these plants in a common garden, and measured defensive and morphological traits. We found some evidence for evolutionary change of defense traits in three of the four species following the exclusion of rabbits. We observed the clearest changes in F. rubra, which showed a 9% decline in tolerance to herbivory and a 26% decline in leaf number. We also observed weak evidence for a change in all grass species towards a more erect growth form suggesting that grazing selects for plants that grow close to the ground. Although our results are most consistent with evolution due to changes in the frequency of alleles and genotypes, we cannot rule out that epigenetic changes (e.g., methylation) or maternal environmental effects also contributed to or caused the observed long-term phenotypic responses. Synthesis: Our study provides an experimental test of the evolutionary effects of an ecologically important herbivore. We found evidence for plant defense evolution following >20 years of rabbit exclusion, however the evidence was only strong in 1 species for multiple traits, weak in all 3 grass species for avoidance, and absent in an herb species. This suggests that the evolutionary effects of an ecologically important herbivore on plants will be variable and difficult to predict in nature.

植物防御性状在宏演化（macroevolution）与微演化（microevolution）的时间尺度上，为应对植食性动物（herbivore）的取食压力而逐步演化形成。尽管已有多项研究探讨了短时间尺度内植食者对植物的演化影响，但鲜有研究通过实验验证：哪些防御性状最易发生演化，以及多个共存物种对植食者是否会表现出趋同的演化响应。本研究依托英国英格兰西尔伍德公园（Silwood Park）的长期野外实验开展相关工作：我们对38块草原样地进行了兔类排除处理，处理时长从不足1年至34年不等。为评估兔类排除对植物防御性状的演化影响，我们从包含以下多年生植物的样地中采集种子：黄花茅（Anthoxanthum odoratum L.，禾本科（Poaceae））、紫羊茅原亚种（Festuca rubra L. spp. rubra，禾本科（Poaceae））、绒毛草（Holcus lanatus L.，禾本科（Poaceae））以及禾叶繁缕（Stellaria graminea L.，石竹科（Caryophyllaceae））。随后我们将这些植物种植于同质种植园（common garden）中，并测定其防御性状与形态性状。研究发现，兔类排除后，4个供试物种中有3个的防御性状出现了演化改变的证据。其中紫羊茅的性状变化最为显著：其植食耐受性下降了9%，叶片数量减少了26%。我们还观测到，所有禾本科物种均呈现出向更直立生长型转变的微弱趋势，这表明放牧会筛选出贴近地面生长的植株。尽管本研究结果最符合等位基因（allele）与基因型（genotype）频率改变所驱动的演化过程，但我们无法排除表观遗传变化（epigenetic changes，如甲基化（methylation）修饰）或母本环境效应（maternal environmental effects）同样参与或导致了观测到的长期表型响应（phenotypic responses）。综合分析：本研究为生态系统关键植食者对植物的演化影响提供了实验验证。我们发现，在兔类排除超过20年后，植物防御性状确实发生了演化，但相关证据仅在1个物种的多个性状中表现显著：3个禾本科物种的防御规避性状仅呈现微弱证据，而禾叶繁缕这一草本物种则未出现明显的演化响应。这表明，生态系统关键植食者对植物的演化影响在自然环境中存在显著异质性，且难以被精准预测。