Ward Philip S, Branstetter Michael G
Department of Entomology and Nematology, University of California, Davis, CA 95616, USA
Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.
Proc Biol Sci. 2017 Mar 15;284(1850). doi: 10.1098/rspb.2016.2569.
Phylogenetic and biogeographic analyses can enhance our understanding of multispecies interactions by placing the origin and evolution of such interactions in a temporal and geographical context. We use a phylogenomic approach-ultraconserved element sequence capture-to investigate the evolutionary history of an iconic multispecies mutualism: Neotropical acacia ants ( group) and their associated hostplants. In this system, the ants receive shelter and food from the host plant, and they aggressively defend the plant against herbivores and competing plants. We confirm the existence of two separate lineages of obligate acacia ants that convergently occupied and evolved plant-protecting behaviour, from timid ancestors inhabiting dead twigs in rainforest. The more diverse of the two clades is inferred to have arisen in the Late Miocene in northern Mesoamerica, and subsequently expanded its range throughout much of Central America. The other lineage is estimated to have originated in southern Mesoamerica about 3 Myr later, apparently piggy-backing on the pre-existing mutualism. Initiation of the / interaction involved a shift in the ants from closed to open habitats, into an environment with more intense plant herbivory. Comparative studies of the two lineages of mutualists should provide insight into the essential features binding this mutualism.
系统发育和生物地理学分析可以通过将多物种相互作用的起源和演化置于时间和地理背景中，来增强我们对这些相互作用的理解。我们采用一种系统基因组学方法——超保守元件序列捕获——来研究一种标志性的多物种互利共生关系的进化历史：新热带区的金合欢蚁（群体）及其相关的寄主植物。在这个系统中，蚂蚁从寄主植物那里获得庇护所和食物，并且它们积极地保护植物免受食草动物和竞争性植物的侵害。我们证实了存在两个独立的专性金合欢蚁谱系，它们从栖息在雨林枯枝上的胆小祖先那里趋同地占据并演化出了植物保护行为。这两个分支中更为多样的一个被推断在中新世晚期出现在中美洲北部，随后其分布范围扩展到了中美洲的大部分地区。另一个谱系估计大约在300万年后起源于中美洲南部，显然是借助了已有的互利共生关系。对这两个互利共生者谱系的比较研究应该能够深入了解维系这种互利共生关系的基本特征。
