Data from: Integrative ichthyological species delimitation in the Greenthroat Darter complex (Percidae: Etheostomatinae)

Species delimitation is fundamental to deciphering the mechanisms that
generate and maintain biodiversity. Alpha taxonomy historically relied on
expert knowledge to describe new species using phenotypic and
biogeographic evidence, which has the appearance of investigator
subjectivity. In contrast, DNA‐based methods using the multispecies
coalescent model (MSC) promise a more objective approach to describing
biodiversity. However, recent criticisms suggest that under some
conditions the MSC may over‐split lineages, identifying species that do
not reflect biological reality. Here, we reconcile these approaches using
empirical data for the Greenthroat Darter complex (Etheostoma lepidum), a
small freshwater fish species with a disjunct distribution in Texas and
New Mexico, USA. We demonstrate that MSC methods recognizes all nine
sampled populations as distinct species, sometimes splitting specimens
from a single locality into multiple species. However, environmental,
phenotypic and biogeographic evidence do not corroborate the nine species
supported by the MSC. Instead, collective evidence indicates
that E. lepidum is comprised of just three species that
are consistent with the molecular phylogeny: Etheostoma
lepidum (Greenthroat Darter) in rivers draining the eastern
Edwards Plateau, Etheostoma cf. lepidum (Texas
Darter) in the Concho and San Saba rivers and
Etheostoma cf. lepidum (Pecos Darter) in the
Pecos River. The Pecos Darter is likely highly imperiled due to its
localized distribution and reliance on vanishing spring‐fed stream
habitats. The impending biodiversity crisis makes integrative and swift
species delimitation more necessary than ever. Our study exemplifies how
classic taxonomic expertise combined with molecular phylogenetics can
produce a more robust description of threatened biodiversity.

物种界定是解析生物多样性产生与维持内在机制的核心基础。传统α分类学（Alpha taxonomy）依赖专家知识，结合表型与生物地理学证据描述新物种，但该方法易受研究者主观因素影响。与之相对，基于DNA的多物种溯祖模型（multispecies coalescent model, MSC）方法则有望为生物多样性描述提供更为客观的路径。然而，近期研究指出，在部分情境下MSC可能会过度拆分支系，将并非真实存在的类群认定为独立物种。本研究以美国德克萨斯州与新墨西哥州存在间断分布的小型淡水鱼类——绿喉镖鲈复合群（Greenthroat Darter, *Etheostoma lepidum*）为研究对象，整合两类方法开展分析以达成折中。研究结果显示，MSC方法将全部9个采样种群均认定为独立物种，甚至会将同一采样点的标本拆分为多个物种。但环境、表型与生物地理学证据均无法佐证MSC所支持的9个物种划分方案。综合各类证据表明，*E. lepidum*实际上仅包含3个符合分子系统发育结果的物种：分布于爱德华兹高原东部汇水河流的绿喉镖鲈（Greenthroat Darter, *Etheostoma lepidum*）；分布于康乔河与圣萨巴河的德克萨斯镖鲈（Texas Darter, *Etheostoma cf. lepidum*）；以及分布于佩科斯河的佩科斯镖鲈（Pecos Darter, *Etheostoma cf. lepidum*）。佩科斯镖鲈的分布范围极为局限，且依赖日益缩减的泉水补给溪流生境，因此极有可能面临严重的生存威胁。迫在眉睫的生物多样性危机使得整合式快速物种界定工作的必要性愈发凸显。本研究证明，经典分类学知识与分子系统学方法的结合，能够为受威胁生物多样性的研究提供更为可靠的描述框架。