Maria Salnitska, Angesom Gebremeskel

Quedius umbrinus-complex (Coleoptera, Staphylinidae): updates and insights from nuclear gene data

Introduction

Quedius umbrinus-complex (coleoptera, staphylinidae): updates and insights from nuclear gene data. Updates on Quedius umbrinus-complex (Coleoptera, Staphylinidae) using nuclear gene data. Molecular analyses confirm four species and discuss a Q. pseudoumbrinus subclade.

Abstract

To assess the accuracy of the species composition of the Q. umbrinus complex proposed earlier by us (Salnitska and Solodovnikov 2021) using an integrative approach, we performed additional molecular analyses based on updated mitochondrial COI data and newly obtained nuclear wg data. Only DNA grade material was used in this study, as the combination of morphological and molecular data is necessary for effective species delimitation within this species complex. All phylogenetic analyses based on the separate COI and wg genes and the concatenated dataset confirmed the subdivision into four species: Q. umbrinus, Q. pseudoumbrinus, Q. sigwalti and Q. volkeri. The only discordance in the topologies between mitochondrial and nuclear genes was observed in the monophyly of Q. umbrinus complex which may be explained by conserved nature of nuclear gene. Most phylogenetic and species delimitation analyses revealed a significant subclade within Q. pseudoumbrinus comprising specimens from the Irkutsk Province, namely from the type locality of the already synonymized Q. angaricus. Even though the genetic distance of this subclade from other Q. pseudoumbrinus specimens reaches 4.1 %, we did not resurrect it due to the absence of the any distinct morphological characters.

Review

The submitted manuscript presents an important update and re-evaluation of the *Quedius umbrinus* species complex, building upon previous work by the same authors. By incorporating newly acquired nuclear gene data (wg) alongside updated mitochondrial COI sequences, the study aims to robustly assess the accuracy of previously proposed species delimitations. The explicit reliance on an integrative approach combining molecular and morphological data, utilizing only DNA-grade material, underscores the methodological rigor applied. This work significantly contributes to the systematics of Staphylinidae by providing crucial molecular support for species boundaries within a taxonomically challenging group. A key strength of this study lies in its multi-locus molecular approach. The consistent support from separate COI, wg, and concatenated phylogenetic analyses for the subdivision into four distinct species – *Q. umbrinus, Q. pseudoumbrinus, Q. sigwalti*, and *Q. volkeri* – provides strong evidence for their validity. The authors appropriately acknowledge the sole discordance concerning the monophyly of the *Q. umbrinus* complex between mitochondrial and nuclear markers, offering a plausible explanation related to the conserved nature of nuclear genes. A particularly interesting finding is the identification of a significant subclade within *Q. pseudoumbrinus* from the Irkutsk Province, displaying a notable genetic distance of 4.1% from other conspecifics, including specimens from the type locality of the previously synonymized *Q. angaricus*. Despite the substantial genetic divergence observed in the Irkutsk subclade, the authors' decision not to resurrect *Q. angaricus* due to the absence of distinct morphological characters is commendable and reflects a cautious, integrative taxonomic approach. This highlights the ongoing challenge in reconciling genetic patterns with morphological distinctiveness for species delimitation, and the authors' adherence to a holistic definition of species. This study provides a solid foundation for understanding the diversity within the *Q. umbrinus* complex and sets a precedent for how future taxonomic work on similar complexes should integrate various data types. The results are clear, the methods appear sound as described, and the conclusions are well-reasoned given the presented data.

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