Data from: Speciation below ground: tempo and mode of diversification in a radiation of endogean ground beetles

Dispersal is a critical factor determining the spatial scale of speciation, which is constrained by the ecological characteristics and distribution of a species' habitat and the intrinsic traits of species. Endogean taxa are strongly affected by the unique qualities of the below-ground environment and its effect on dispersal, and contrasting reports indicate either high dispersal capabilities favoured by small body size and mediated by passive mechanisms, or low dispersal due to restricted movement and confinement inside the soil. We studied a species rich endogean ground beetle lineage, Typhlocharina, including three genera and more than 60 species, as a model for the evolutionary biology of dispersal and speciation in the deep soil. A time calibrated molecular phylogeny generated from >400 individuals was used to delimit candidate species, to study the accumulation of lineages through space and time by species-area-age relationships, and to determine the geographical structure of the diversification using the relationship between phylogenetic and geographic distances across the phylogeny. Our results indicated a small spatial scale of speciation in Typhlocharina and low dispersal capacity combined with sporadic long distance, presumably passive dispersal events that fuelled the speciation process. Analysis of lineage growth within Typhlocharina revealed a richness plateau correlated with the range of distribution of lineages, suggesting a long-term species richness equilibrium mediated by density dependence through limits of habitat availability. The interplay of area and age dependent processes ruling the lineage diversification in Typhlocharina may serve as a general model for the evolution of high species diversity in endogean mesofauna.

扩散（Dispersal）是决定物种形成空间尺度的关键因素，其受到物种栖息地的生态特征与分布格局，以及物种内在性状的共同制约。内栖类群（Endogean taxa）极易受地下环境的独特属性及其对扩散过程的影响，现有研究结论存在显著分歧：一类观点认为小型体型可赋予其较高扩散能力，并通过被动扩散机制介导；另一类则指出土壤内的活动受限与生境禁锢会导致扩散能力低下。
本研究以物种丰富度极高的内栖步甲支系——盲甲族（Typhlocharina，包含3个属、60余个物种）作为研究模型，探究深层土壤生境中扩散与物种形成的进化生物学机制。研究基于400余个个体构建了时间校准的分子系统发育树，以此界定候选物种，通过物种-面积-年龄关系分析支系随时空的累积动态，并借助系统发育树内系统发育距离与地理距离的关联模式，解析物种分化的地理结构特征。
研究结果显示，盲甲族的物种形成空间尺度较小，扩散能力整体偏低，但偶发的、推测为被动扩散的长距离扩散事件推动了物种形成进程。对盲甲族支系生长的分析发现，物种丰富度平台与支系分布范围呈显著相关，表明栖息地可获得性限制下的密度制约过程介导了长期的物种丰富度平衡。
调控盲甲族支系分化的面积与年龄依赖过程的相互作用，或可作为解释内栖中型动物群（endogean mesofauna）高物种多样性演化的通用模型。