Data from: Timetree of Aselloidea reveals species diversification dynamics in groundwater

A key challenge for biologists is to document and explain global patterns of diversification in a wide range of environments. Here, we explore patterns of continental-scale diversification in a groundwater species-rich clade, the superfamily Aselloidea (Pancrustacea: Isopoda). Our analyses supported a constant diversification rate during most of the course of Aselloidea evolution, until 4–15 Ma when diversification rates started to decrease. This constant accumulation of lineages challenges the view that groundwater species diversification in temperate regions might have been primarily driven by major changes in physical environment leading to the extinction of surface populations and subsequent synchronous isolation of multiple groundwater populations. Rather than acting synchronously over broad geographic regions, factors causing extinction of surface populations and subsequent reproductive isolation of groundwater populations may act in a local and asynchronous manner, thereby resulting in a constant speciation rate over time. Our phylogeny also revealed several cases of parapatric distributions among closely related surface-water and groundwater species suggesting that species diversification could also arise from a process of disruptive selection along the surface-subterranean environmental gradient. Our results call for re-evaluating the spatial scale and timing of factors causing diversification events in groundwater.

生物学家面临的一项核心挑战，是记录并解释广泛环境下的全球物种多样化格局。本研究针对一类地下水物种丰富的演化支——潮虫总科（Aselloidea，泛甲壳类：等足目）的大陆尺度多样化格局展开探究。分析结果显示，潮虫总科的演化历程中，绝大多数时期的多样化速率保持恒定，直至距今4~15 Ma（百万年前）时，多样化速率才开始下降。这种类群的持续积累，对“温带地区地下水物种的多样化主要由物理环境的重大变化驱动——此类变化导致地表种群灭绝，进而同步隔离多个地下水种群”这一观点提出了挑战。研究表明，导致地表种群灭绝、后续引发地下水种群生殖隔离的因素，并非在广阔地理区域内同步发挥作用，而是以局域且异步的方式进行，由此随时间推移维持了恒定的物种形成速率。本研究的系统发育（phylogeny）分析还揭示了多组亲缘关系紧密的地表水生与地下水物种存在邻域分布（parapatric distributions）的案例，这表明物种多样化也可能源自沿地表-地下环境梯度的歧化选择（disruptive selection）过程。本研究结果呼吁重新评估驱动地下水物种多样化事件的空间尺度与发生时机。