Data from: Geographic mosaic of plant evolution: extrafloral nectary variation mediated by ant and herbivore assemblages

Herbivory is an ecological process that is known to generate different patterns of selection on defensive plant traits across populations. Studies on this topic could greatly benefit from the general framework of the Geographic Mosaic Theory of Coevolution (GMT). Here, we hypothesize that herbivory represents a strong pressure for extrafloral nectary (EFN) bearing plants, with differences in herbivore and ant visitor assemblages leading to different evolutionary pressures among localities and ultimately to differences in EFN abundance and function. In this study, we investigate this hypothesis by analyzing 10 populations of Anemopaegma album (30 individuals per population) distributed through ca. 600 km of Neotropical savanna and covering most of the geographic range of this plant species. A common garden experiment revealed a phenotypic differentiation in EFN abundance, in which field and experimental plants showed a similar pattern of EFN variation among populations. We also did not find significant correlations between EFN traits and ant abundance, herbivory and plant performance across localities. Instead, a more complex pattern of ant–EFN variation, a geographic mosaic, emerged throughout the geographical range of A. album. We modeled the functional relationship between EFNs and ant traits across ant species and extended this phenotypic interface to characterize local situations of phenotypic matching and mismatching at the population level. Two distinct types of phenotypic matching emerged throughout populations: (1) a population with smaller ants (Crematogaster crinosa) matched with low abundance of EFNs; and (2) seven populations with bigger ants (Camponotus species) matched with higher EFN abundances. Three matched populations showed the highest plant performance and narrower variance of EFN abundance, representing potential plant evolutionary hotspots. Cases of mismatched and matched populations with the lowest performance were associated with abundant and highly detrimental herbivores. Our findings provide insights on the ecology and evolution of plant–ant guarding systems, and suggest new directions to research on facultative mutualistic interactions at wide geographic scales.

植食作用是一种生态过程，已知其可在不同种群间塑造植物防御性状的选择模式。针对该主题的研究若能借助协同进化地理镶嵌理论（Geographic Mosaic Theory of Coevolution，GMT）的通用分析框架，将极大推动相关研究进展。在此，我们提出假说：植食作用对携带花外蜜腺（extrafloral nectary，EFN）的植物构成强烈选择压力；不同地域的植食者与访蚁类群组成存在差异，会带来差异化的进化压力，最终导致花外蜜腺的多度与功能产生分化。本研究围绕该假说展开探究，我们分析了分布于新热带稀树草原约600公里范围内的10个白花紫葳（Anemopaegma album）种群（每个种群含30个个体），样本覆盖该物种的大部分地理分布范围。同质园实验（common garden experiment）结果显示，花外蜜腺多度存在表型分化：野外植株与实验植株在种群间的花外蜜腺变异模式高度相似。我们未检测到花外蜜腺性状与蚂蚁多度、植食作用强度及植株表现之间存在显著的地域相关性。与之相反，在白花紫葳的整个地理分布范围内，呈现出更为复杂的蚂蚁-花外蜜腺变异格局，即地理镶嵌模式。我们构建了不同蚂蚁物种间花外蜜腺与蚂蚁性状的函数关系模型，并将这一表型互作界面拓展至种群水平，以表征各局部区域的表型匹配与不匹配情况。研究共发现两类截然不同的表型匹配类型：（1）1个由小型蚂蚁（Crematogaster crinosa）组成的种群，其花外蜜腺多度较低，与该蚂蚁类群相匹配；（2）7个由大型蚂蚁（Camponotus物种）组成的种群，其花外蜜腺多度较高，与该蚂蚁类群相匹配。其中3个匹配种群展现出最高的植株表现及最低的花外蜜腺多度变异幅度，代表潜在的植物进化热点区域。而表现最差的匹配与不匹配种群，则与多度高且危害极强的植食者类群相关联。本研究结果为植物-蚂蚁守卫系统的生态学与进化研究提供了新视角，并为大地理尺度下兼性互利共生相互作用的相关研究指明了新方向。