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.

中文翻译：

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Greenthroat Darter 复合体中的综合鱼类物种定界（鲈科：Etheostomatinae）

物种定界是破译产生和维持生物多样性的机制的基础。Alpha 分类法历来依靠专家知识使用表型和生物地理证据来描述新物种，这具有研究者主观性的外观。相比之下，使用多物种聚结模型 (MSC) 的基于 DNA 的方法有望提供一种更客观的方法来描述生物多样性。然而，最近的批评表明，在某些情况下，MSC 可能会过度分裂谱系，识别出不反映生物现实的物种。在这里，我们使用 Greenthroat Darter 复合体（Etheostoma lepidum)，一种小型淡水鱼，在美国德克萨斯州和新墨西哥州有间断分布。我们证明 MSC 方法将所有九个采样种群识别为不同的物种，有时将单个地点的标本分成多个物种。然而，环境、表型和生物地理证据并不能证实 MSC 支持的九种物种。相反，集体证据表明E. lepidum仅由三个与分子系统发育一致的物种组成：Etheostoma lepidum (Greenthroat Darter) 在爱德华兹高原东部排水的河流中，Etheostoma cf. Concho 和 San Saba 河中的lepidum (Texas Darter) 和Etheostoma cf。佩科斯河中的lepidum (Pecos Darter)。由于其局部分布和依赖消失的泉水溪流栖息地，Pecos Darter 可能非常危险。迫在眉睫的生物多样性危机使得综合和快速的物种划界比以往任何时候都更加必要。我们的研究举例说明了经典的分类学专业知识与分子系统发生学相结合如何能够对受威胁的生物多样性产生更可靠的描述。