Integrative taxonomy reveals inflated biodiversity in the European Temnothorax unifasciatus complex (Hymenoptera: Formicidae)

Temnothorax unifasciatus (Latreille, 1798) is a widely distributed pan-European species from the Iberian Peninsula to the Caucasus. This taxon's relatively high morphological variability prompts the taxonomists of earlier times and today to mention the morphologically different elements at specific or subspecific ranks. This paper aims to understand the population structure and genetic diversity within this lineage via an integrative taxonomy, incorporating molecular phylogenetics, species delimitation analyses, and multivariate analyses of continuous morphometric data from across the geographic range of the T. unifasciatus complex. Phylogenetic analyses yielded incongruent trees. The genealogical diversity index (gdi) and the confirmatory analyses on morphological data found only weak, ambiguous delimitations within the unifasciatus group. The most highly supported scenario splits T. brackoi from the remaining unifasciatus group with ambiguous support (gdi = 0.56). This scenario is supported by multivariate morphometry with 100% accuracy in classification success. Instead, our results suggest complex morphological and genetic population structuring within the broad range of T. unifasciatus. Therefore, we confirm the validity of two species, T. brackoi Salata & Borowiec, 2019 and T. unifasciatus (Latreille, 1798), and propose five new junior synonymies, T. cordieri (Bondroit, 1918) syn. nov., T. tauricus (Ruzsky, 1902) syn. nov., T. berlandi (Bondroit, 1918) syn. nov., T. unifasciatus staegeri (Bondroit, 1918) syn. nov., T. tuberum ciscaucasicus (Arnol'di, 1977) syn. nov. with the latter. In order to achieve maximal taxonomic stability, we designated a lectotype for Temnothorax unifasciatus (Latreille, 1798).

单带凹胸切叶蚁（Temnothorax unifasciatus）(Latreille, 1798)是一类广布于泛欧洲区域的物种，分布范围从伊比利亚半岛延伸至高加索地区。该类群较高的形态变异度，使得古今分类学者均将其形态分化显著的类群界定为独立种或亚种阶元。本研究旨在通过整合分类学方法，结合分子系统发育学、物种界定分析以及对单带凹胸切叶蚁复合群全地理分布范围内的连续形态测量数据开展多元分析，解析该支系的种群结构与遗传多样性。系统发育分析得到了拓扑结构不一致的系统发育树。谱系多样性指数（genealogical diversity index，GDI）以及形态数据验证分析结果显示，单带凹胸切叶蚁类群内部仅存在微弱且模糊的类群界定信号。支持度最高的演化场景将布拉科凹胸切叶蚁（T. brackoi）从其余单带凹胸切叶蚁类群中分离出来，但该场景的支持度仅为模糊级别（GDI=0.56）。而多元形态测量分析则以100%的分类正确率支持该演化场景。与之相反，本研究结果表明，广布的单带凹胸切叶蚁类群内部存在复杂的形态与遗传种群结构。据此，本研究确认了两个有效种：布拉科凹胸切叶蚁（T. brackoi Salata & Borowiec, 2019）与单带凹胸切叶蚁（Temnothorax unifasciatus, Latreille, 1798），并提出5个新的同物异名：科尔迪耶凹胸切叶蚁（T. cordieri (Bondroit, 1918) syn. nov.）、塔乌里凹胸切叶蚁（T. tauricus (Ruzsky, 1902) syn. nov.）、贝朗德凹胸切叶蚁（T. berlandi (Bondroit, 1918) syn. nov.）、施塔格尔单带凹胸切叶蚁（T. unifasciatus staegeri (Bondroit, 1918) syn. nov.）以及高加索块茎凹胸切叶蚁（T. tuberum ciscaucasicus (Arnol'di, 1977) syn. nov.），上述类群均归并入单带凹胸切叶蚁。为最大限度保障分类学稳定性，本研究为单带凹胸切叶蚁（Temnothorax unifasciatus, Latreille, 1798）指定了选模标本。