Department of Integrative Biology, The University of Texas at Austin, Austin, TX 78712;
Biodiversity Center, The University of Texas at Austin, Austin, TX 78712.
Proc Natl Acad Sci U S A. 2019 Feb 12;116(7):2624-2633. doi: 10.1073/pnas.1815014116. Epub 2019 Jan 14.
Groundwater-dependent species are among the least-known components of global biodiversity, as well as some of the most vulnerable because of rapid groundwater depletion at regional and global scales. The karstic Edwards-Trinity aquifer system of west-central Texas is one of the most species-rich groundwater systems in the world, represented by dozens of endemic groundwater-obligate species with narrow, naturally fragmented distributions. Here, we examine how geomorphological and hydrogeological processes have driven population divergence and speciation in a radiation of salamanders () endemic to the Edwards-Trinity system using phylogenetic and population genetic analysis of genome-wide DNA sequence data. Results revealed complex patterns of isolation and reconnection driven by surface and subsurface hydrology, resulting in both adaptive and nonadaptive population divergence and speciation. Our results uncover cryptic species diversity and refine the borders of several threatened and endangered species. The US Endangered Species Act has been used to bring state regulation to unrestricted groundwater withdrawals in the Edwards (Balcones Fault Zone) Aquifer, where listed species are found. However, the Trinity and Edwards-Trinity (Plateau) aquifers harbor additional species with similarly small ranges that currently receive no protection from regulatory programs designed to prevent groundwater depletion. Based on regional climate models that predict increased air temperature, together with hydrologic models that project decreased springflow, we conclude that Edwards-Trinity salamanders and other codistributed groundwater-dependent organisms are highly vulnerable to extinction within the next century.
依赖地下水的物种是全球生物多样性中了解最少的组成部分之一，也是一些最脆弱的物种之一，因为在区域和全球范围内地下水迅速枯竭。德克萨斯州中西部的岩溶爱德华兹-三一含水层系统是世界上物种最丰富的地下水系统之一，拥有数十种特有地下水专性物种，其分布范围狭窄，自然碎片化。在这里，我们使用全基因组 DNA 序列数据的系统发育和种群遗传分析，研究地貌和水文地质过程如何驱动爱德华兹-三一系统特有辐射的蝾螈种群的分歧和物种形成。结果揭示了由地表水和地下水驱动的隔离和再连接的复杂模式，导致适应性和非适应性种群的分歧和物种形成。我们的研究结果揭示了隐藏的物种多样性，并细化了几种受威胁和濒危物种的边界。美国濒危物种法案已被用于对发现有受保护物种的爱德华兹含水层（巴伦科内斯断层带）的不受限制的地下水开采进行州级监管。然而，三一含水层和爱德华兹-三一（高原）含水层还拥有其他同样范围较小的物种，目前不受旨在防止地下水枯竭的监管计划的保护。基于预测空气温度升高的区域气候模型，以及预测春季流量减少的水文模型，我们得出结论，爱德华兹-三一蝾螈和其他共同分布的依赖地下水的生物在未来一个世纪内极有可能灭绝。
