1. The Yucatán Peninsula (YP) contains one of the most spectacular and developed karstic aquifers in the world, which connects to the surface through water‐filled sinkholes locally known as cenotes. Cenotes and their associated submerged caves are home to a remarkable diversity of aquatic fauna, yet very little is known about spatial patterns of intraspecific genetic and morphological variation across the aquifer. The strong affinity to cenotes (vs. submerged caves) exhibited by most fishes inhabiting the YP aquifer raises a fundamental question about the ecology and evolutionary history of its ichthyofauna: how genetically structured and morphologically divergent are fish populations from different cenotes across the YP? To shed light on this question, we investigated phylogeographic structure in the Neotropical catfish Rhamdia guatemalensis, arguably the most ubiquitous representative of the YP aquifer ichthyofauna.
2. Geographic patterns of genetic variation were determined through phylogeographic and population genetics analyses of mitochondrial (mt)DNA sequence data. Body shape variation was investigated using both traditional and geometric morphometrics. Dense sampling across the previously overlooked YP region, coupled with the inclusion of samples from basins unrepresented in past studies, allowed for revision of previous estimates of phylogeographic structuring across the species’ range.
3. Our results reveal a striking spatial correspondence between major mtDNA lineages and physiographic regions defined on the basis of broad‐scale patterns of groundwater flow. Morphological variation in populations from the YP, although considerable, neither reflects the observed spatial signal of genetic differentiation nor displays any other discernible geographic pattern. The resulting range‐wide phylogeographic pattern is largely consistent with a latitudinal, isolation‐by‐distance gradient, and the expectations from catchment hydrology, while revealing an unexpectedly close relationship between YP aquifer and epigean populations (both inside and outside the YP).
4. Although the inferred range‐wide phylogeographic history is consistent with a single aquifer colonisation event followed by multiple instances of dispersal out of the aquifer and into neighbouring epigean basins, hypotheses regarding the colonisation and exodus of the YP by R. guatemalensis require further investigation. Within the YP aquifer, regional‐scale hydrogeological differences might impose limits to underground dispersal, potentially driving genetic divergence in populations of R. guatemalensis, and possibly in other cenote‐dwelling fishes as well. Future research focused on other YP aquifer species, however, is needed to test the generality of our findings.
5. Phylogeographic research on the stygofauna of the YP aquifer is a relatively nascent field of inquiry. Besides shedding novel light into the patterns and drivers of genetic differentiation in fish populations from across the aquifer, this study sets the stage for future research aimed at unravelling the evolutionary history of the stygofauna that inhabits the cenotes and submerged caves of the YP. The remarkable and hitherto undocumented phylogeographic pattern revealed herein (i.e. correspondence of major mtDNA lineages with physiographic regions defined by regional‐scale fracture zones) adds to a growing body of evidence in support of the notion that the architecture of freshwater aquifers may include physical barriers that can act as regional‐scale drivers of groundwater faunal distributions and genetic structuring.

中文翻译：

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墨西哥尤卡坦半岛的cenotes的新热带cat鱼Rhamdia guatemalensis（Siluriformes：Heptapteridae）的植物地理结构驱动力的区域尺度含水层水文地质学。

1. 尤卡坦半岛（YP）包含世界上最壮观，最发达的岩溶含水层之一，该岩溶含水层通过充满水的沉陷坑连接到地表，这些沉陷坑在当地被称为cenotes。Cenotes及其相关的水下洞穴是众多水生动物的家园，但对整个含水层种内遗传和形态变异的空间格局知之甚少。大多数居住在YP蓄水层中的鱼类对粪便的强烈亲和力（相对于被淹没的洞穴）提出了一个关于其鱼鳞鱼生态学和进化史的根本问题：来自整个YP的不同粪便的鱼类种群在遗传结构和形态上有何差异？为了阐明这个问题，我们研究了新热带cat鱼的系统地理结构Rhamdia危地马拉，可以说是YP含水层ichthyofauna的最普遍代表。
2. 遗传变异的地理模式是通过线粒体（mt）DNA序列数据的系统地理学和群体遗传学分析确定的。使用传统形态学和几何形态学方法研究了身体形状的变化。在以前被忽视的YP区域进行密集采样，再加上过去研究中未曾描述的盆地样本，可以对物种范围内的植物学构造进行先前的估算。
3. 我们的研究结果揭示了主要的mtDNA谱系与根据广泛的地下水流模式定义的地理区域之间惊人的空间对应关系。YP种群的形态变化虽然很大，但既不能反映观察到的遗传分化空间信号，也不能显示任何其他可辨别的地理格局。由此产生的范围广泛的植物学格局在很大程度上与纬度，距离隔离和来自流域水文学的期望相一致，同时揭示了YP蓄水层与表皮种群（YP内部和外部）之间出乎意料的紧密关系。
4. 尽管推断的全系统地理记录历史与单个含水层定植事件相一致，然后多次扩散出含水层并进入邻近的Epigean盆地，但有关危地马拉R.YP的定殖和外流的假设仍需进一步研究。在YP含水层中，区域规模的水文地质差异可能会限制地下扩散，从而有可能导致危地马拉R.危地马拉种群以及其他居住在巢穴中的鱼类的遗传差异。然而，需要进一步研究其他YP含水层物种，以检验我们发现的一般性。
5. YP含水层的茎部动物的系统地理学研究是一个相对新兴的研究领域。除了为整个蓄水层中鱼类种群的遗传分化模式和动因提供新颖的解释外，本研究还为将来的研究奠定了基础，该研究旨在揭露居住在YP的山洞和淹没洞穴中的stygofauna的进化历史。本文揭示的显着且迄今未记录的植物学谱型（即主要线粒体DNA谱系与区域尺度断裂带所定义的生理学区域的对应关系）增加了越来越多的证据，以支持淡水含水层的结构可能包括物理屏障的观点。可以作为区域范围的地下水动植物分布和遗传结构驱动因素。