Molecular phylogeography of myrmecophyte-ant-scale insect tripartite symbiosis in Southeast Asian tropical forests

许多热带植物为蚂蚁提供住所，从而保护它们免受食草动物的侵害。大多数这些金蚁系统包括蚧虫作为第三个伙伴。介壳虫生活在植物的空心茎中，吮吸植物的汁液，并为蚂蚁提供蜜露。我们研究了麦卡兰加（Macaranga）植物、它们的居民Crematogaster （Decacrema）蚂蚁和滋养体球菌蚧虫之间三方相互作用的进化。以前的研究表明，这三个属有紧密的联系，尽管有时涉及其他一些属。综合取样的蚂蚁和鳞片的mtDNA COI系统发育分别显示了10个和5个得到良好支持的谱系。两种系统发育的比较和已发表的Maearanga系统发育的比较表明没有共种。虽然蚂蚁尺度和植物尺度的相互作用是分散的，但蚂蚁尺度的相互作用是特定的，因为寄主的转移受到植物茎性状的限制，而这些性状本身与Macaranga系统发育相关。根据COI分化率1.5% / m， Macaranga的Decacrema鳞片和Coccus鳞片分别至少有12和10 m的历史，表明它们从中新世中期开始在东南亚湿森林群落中同时多样化。

Many tropical plants house ants and thereby gain protection from herbivores. Most of these myrmecophyte-ant systems include scale insects as the third associate. Scale insects live inside the plant hollow stem, suck the plant sap, and provide honeydew to the ants. We investigate the evolution of the three-way interaction among myrmecophytic Macaranga plants, their inhabitant Crematogaster (Decacrema) ants, and the trophobiont Coccus scale insects. Previous studies show that these three genera have a tight association although a few other genera are sometimes involved.The mtDNA COI phylogenies of comprehensively-sampled ants and scales reveal ten and five well-supported lineages, respectively. Comparisons of the two phylogenies and a published Maearanga phylogeny indicate an absence of cospeciation. Whereas the ant-scale and plant-scale interactions are diffuse, the ant-plant one is specific in the sense that host shifts have been constrained by plant stem traits that are themselves correlated with Macaranga phylogeny. Applying COI divergence rates of 1.5% per My, the Decacrema ants and the Coccus scales from Macaranga are inferred to be at least 12, and 10 My old, respectively, indicating that they have been diversifying contemporaneously since the mid-Miocene in the wet forest community of Southeast Asia.