Phylogeographic concordance factors quantify phylogeographic congruence among co-distributed species in the Sarracenia alata pitcher plant system

Comparative phylogeographic investigations have identified congruent phylogeographic breaks in co-distributed species in nearly every region of the world. The qualitative assessments of phylogeographic patterns traditionally used to identify such breaks, however, are limited because they rely on identifying monophyletic groups across species and do not account for coalescent stochasticity. Only long-standing phylogeographic breaks are likely to be obvious; many species could have had a concerted response to more recent landscape events, yet possess subtle signs of phylogeographic congruence because ancestral polymorphism has not completely sorted. Here we introduce Phylogeographic Concordance Factors (PCFs), a novel method for quantifying phylogeographic congruence across species. We apply this method to the Sarracenia alata pitcher plant system, a carnivorous plant with a diverse array of commensal organisms. We explore whether a group of ecologically associated arthropods have co-diversified with the host pitcher plant, and identify if there is a positive correlation between ecological interaction and PCFs. Results demonstrate that multiple arthropods share congruent phylogeographic breaks with S. alata, and provide evidence that the level of ecological association can be used to predict the degree of similarity in the phylogeographic pattern. This study outlines an approach for quantifying phylogeographic congruence, a central concept in biogeographic research.

比较系统发生生物地理学研究已证实，全球几乎所有区域的同分布物种中均存在一致的系统发生生物地理学断裂带。不过，传统上用于识别此类断裂带的系统发生生物地理学格局定性评估方法存在局限，这类方法依赖于跨物种识别单系群，且未考虑溯祖随机性；仅长期存续的系统发生生物地理学断裂带才容易被辨识，诸多物种或已对近期景观事件产生协同响应，但因祖先多态性尚未完全分选，其系统发生生物地理学一致性的信号较为微弱。本研究提出系统发生生物地理学一致性因子（Phylogeographic Concordance Factors, PCFs），这是一种可量化跨物种系统发生生物地理学一致性的全新方法。我们将该方法应用于黄瓶子草（Sarracenia alata）系统——一种拥有多样偏利共生生物的食肉植物，旨在探究一组生态相关的节肢动物是否与宿主黄瓶子草发生共同分化，并明确生态相互作用强度与PCFs之间是否存在正相关关系。研究结果显示，多种节肢动物与黄瓶子草（S. alata）存在一致的系统发生生物地理学断裂带，并证实生态关联程度可用于预测系统发生生物地理学格局的相似性。本研究提出了一种量化系统发生生物地理学一致性的方法，而该一致性是生物地理学研究的核心概念。