Spatial phylogenomics of acrobat ants in Madagascar—mountains function as cradles for recent diversity and endemism

Aim: A crucial step to protecting biodiversity is assessing species diversity and endemism. We delineate spatial patterns of diversity in Malagasy ants on a phylogenetic and taxonomic level to identify centers of diversity and endemism, and evaluate the ‘museum vs cradle’ hypothesis with regard to ant endemism. Location: Madagascar Taxon: Ants, genus Crematogaster. Methods: We estimated distribution models for 33 Crematogaster species and generated a phylogeny based on ultraconserved elements. We calculated species richness (SR), phylogenetic diversity (PD), weighted (WE), phylogenetic endemism(PE), randomized phylogenetic diversity (PD-sig), and relative phylogenetic diversity (RPD) and endemism (RPE). Categorical analyses of neo- and paleo-endemism (CANAPE) and the phylo-jaccard index were used to delineate centers of neo- and paleo-endemism. We correlated these measures with elevation metrics to investigate the role of mountains in generating ant endemism. Results: We found extensive phylogenetic clustering (significantly low PD-sig) and short branches (low RPD) at higher elevations in central and south-central to southern Madagascar. In contrast, phylogenetic overdispersion (significantly high PD-sig) and long branches (high RPD) predominate at lower elevations in eastern humid and northern western dry forests. CANAPE and phylo-jaccard estimated five centers of endemism, whereby neo- and mixed endemism were significantly correlated with higher elevations, and paleo-endemism with lower elevations. Main Conclusions: Centers of ant endemism are located in western dry and humid forests of northern Madagascar, eastern humid forests, and in the southern Central Highland region. Mountainous areas appear to be cradles of recent diversification for acrobat ants, whereas lower elevations may be regarded as centers of paleo-endemism and thus museums for relict lineages. Species diversification among acrobat ants may have coincided with the arrival of a new biome in the central highlands of Madagascar.研究目标：保护生物多样性的核心步骤之一是评估物种多样性与特有性。本研究从系统发育与分类学层面刻画马达加斯加蚂蚁的多样性空间格局，以明确多样性与特有性核心区域，并针对蚂蚁特有性验证“博物馆与演化摇篮”假说。 研究区域：马达加斯加 研究类群：蚂蚁，举腹蚁属（Crematogaster） 研究方法：本研究为33个举腹蚁属物种构建了物种分布模型，并基于超保守元件（ultraconserved elements）构建系统发育树。计算了物种丰富度（species richness, SR）、系统发育多样性（phylogenetic diversity, PD）、加权特有性（weighted endemism, WE）、系统发育特有性（phylogenetic endemism, PE）、随机化系统发育多样性（randomized phylogenetic diversity, PD-sig）、相对系统发育多样性（relative phylogenetic diversity, RPD）以及相对特有性（relative endemism, RPE）。采用新特有与古特有分类分析（categorical analyses of neo- and paleo-endemism, CANAPE）与系统发育雅卡尔指数（phylo-jaccard index）来划定新特有与古特有核心区域。同时将上述指标与海拔数据进行相关性分析，以探究山地在驱动蚂蚁特有性形成中的作用。 研究结果：在马达加斯加中部、中南部至南部的高海拔区域，我们观测到显著的系统发育聚集现象（PD-sig值显著偏低）以及较短的分支长度（RPD值偏低）。与之相反，在东部湿润森林与北部西部干旱森林的低海拔区域，则以系统发育弥散现象（PD-sig值显著偏高）与较长的分支长度（RPD值偏高）为主。CANAPE分析与系统发育雅卡尔指数共划定了5个特有性核心区域，其中新特有与混合特有类型与高海拔区域显著相关，而古特有类型则与低海拔区域显著相关。 主要结论：蚂蚁特有性核心区域分布于马达加斯加北部的干旱与湿润森林、东部湿润森林以及南部中央高地区域。山地生境似乎是举腹蚁近期物种分化的演化摇篮，而低海拔区域则可被视为古特有性中心，即孑遗谱系的演化博物馆。举腹蚁属的物种分化事件或与马达加斯加中央高地新生物群系的形成时间相吻合。