Delimitation despite discordance: Evaluating the species limits of a confounding species complex in the face of mitonuclear discordance

The delimitation of species is an essential pursuit of biology, and proper taxonomies are crucial for the assessment and conservation management of organismal diversity. However, delimiting species can be hindered by a number of factors including highly conserved morphologies (e.g. cryptic species), differences in criteria of species concepts, and discordance between gene topologies (e.g. mitonuclear discordance). Here we use a taxonomically confounded species complex of toads in Central America that exhibits extensive mitonuclear discordance to test delimitation hypotheses. Our investigation integrates mitochondrial sequences, nuclear SNPs, morphology, and macroecological data to determine which taxonomy best explains the divergence and evolutionary relationships among these toads. We found that a three species taxonomy following the distributions of the nuclear SNP haplotypes offer the best explanation of the species in this complex based off of the integrated data types. Due to the taxonomic instability of this group we also discuss conservation concerns in the face of improper taxonomic delimitation. Our study provides an empirical hypothesis testing framework to assess species delimitation hypotheses in the face of cryptic morphology and mitonuclear discordance and highlights the importance that proper taxonomy has over conservation related actions.

物种界定是生物学的核心研究议题，合理的分类系统对于生物多样性评估与保护管理至关重要。然而，物种界定工作常受诸多因素阻碍，例如高度保守的形态特征（如隐存种（cryptic species））、不同物种概念的判定标准差异，以及基因拓扑结构间的不一致性（如核质冲突（mitonuclear discordance））。本研究以中美洲一类存在广泛核质冲突、分类学界定混乱的蟾蜍物种复合群为研究对象，用以检验物种界定假说。本研究整合线粒体序列、核单核苷酸多态性（nuclear SNPs）、形态学数据与宏观生态学数据，以明确何种分类系统最能阐释该类蟾蜍的物种分化与演化关系。研究结果显示，基于核单核苷酸多态性单倍型分布的三物种分类方案，在整合多类数据后，最能解释该物种复合群的物种划分问题。鉴于该类群的分类学不稳定性，本研究还探讨了不当物种界定所引发的保护关切。本研究构建了一套可用于评估隐存形态与核质冲突背景下物种界定假说的实证检验框架，并强调了合理分类系统对保护相关行动的重要意义。