Data from: Plant–insect interactions: double-dating associated insect and plant lineages reveals asynchronous radiations

An increasing number of plant-insect studies using phylogenetic analysis suggest that cospeciation events are rare in plant–insect systems. Instead, nonrandom patterns of phylogenetic congruence are produced by phylogenetically conserved host switching (to related plants) or tracking of particular resources or traits (e.g., chemical). The dominance of host switching in many phytophagous insect groups may make the detection of genuine cospeciation events difficult. One important test of putative cospeciation events is to verify whether reciprocal speciation is temporally plausible. We explored techniques for double-dating of both plant and insect phylogenies. We use dated molecular phylogenies of a psyllid (Hemiptera)–Genisteae (Fabaceae) system, a predominantly monophagous insect–plant association widespread on the Atlantic Macaronesian islands. Phylogenetic reconciliation analysis suggests high levels of parallel cladogenesis between legumes and psyllids. However, dating using molecular clocks calibrated on known geological ages of the Macaronesian islands revealed that the legume and psyllid radiations were not contemporaneous but sequential. Whereas the main plant radiation occurred some 8 million years ago, the insect radiation occurred about 3 million years ago. We estimated that >60% of the psyllid speciation has resulted from host switching between related hosts. The only evidence for true cospeciation is in the much more recent and localized radiation of genistoid legumes in the Canary Islands, where the psyllid and legume radiations have been partially contemporaneous. The identification of specific cospeciation events over this time period, however, is hindered by the phylogenetic uncertainty in both legume and psyllid phylogenies due to the apparent rapidity of the species radiations.

越来越多采用系统发育分析（phylogenetic analysis）的植物-昆虫研究表明，植物-昆虫体系中的共成种事件（cospeciation）十分罕见。与之相对，系统发育一致性的非随机模式，主要源于两类过程：一是系统发育保守的宿主切换（host switching）行为，即转向近缘植物宿主；二是对特定资源或性状（如化学物质）的追踪。许多植食性昆虫类群中宿主切换占据主导地位，这可能会使得真正的共成种事件难以被有效检测。验证互惠式物种形成在时间维度上是否合理，是检验推测共成种事件的一项核心手段。我们探索了可同时对植物与昆虫系统发育进行定年的技术方案。本次研究选用了木虱（psyllid，半翅目Hemiptera）-金雀儿族（Genisteae，豆科Fabaceae）体系的定年分子系统发育（molecular phylogenies）数据：该体系以单食性昆虫-植物关联为主要特征，广泛分布于大西洋马卡罗尼西亚群岛（Atlantic Macaronesian islands）。系统发育协同匹配分析（phylogenetic reconciliation analysis）结果显示，豆科植物与木虱之间存在高度水平的平行分支演化。然而，基于马卡罗尼西亚群岛已知地质年龄校准分子钟（molecular clocks）后的定年结果显示，豆科植物与木虱的辐射演化（radiation）并非同步发生，而是具有先后时序：主要的植物辐射演化发生于约800万年前，而昆虫辐射演化则发生在约300万年前。我们估算，超过60%的木虱物种形成事件均源于近缘宿主间的宿主切换。目前唯一可证实真正共成种的证据，来自加那利群岛中更为新近且局域化的金雀儿类豆科植物辐射演化事件——在此区域内，木虱与豆科植物的辐射演化曾部分同步发生。不过，由于此次物种辐射演化速度极快，导致豆科植物与木虱的系统发育均存在显著不确定性，这使得该时期内特定共成种事件的识别工作受到了阻碍。