Passive collecting methods coupled with integrative taxonomy effective in uncovering species diversity of mysteriously paedomorphic beetles

Abstract The genus Diplocladon Gorham, 1883 (Coleoptera: Rhagophthalmidae) is a fascinating group of paedomorphic beetles, and holds potential as an ideal bioindicator for biodiversity conservation. Despite its ecological significance, the species diversity within this genus has remained poorly understood because of their cryptic habitats and challenges in species delimitations. In the present study, we integrate various methodological approaches including morphology, mitochondrial genome-based phylogeny and model-based species delimitations (bPTP, mPTP, GMYC , and BPP ), as well as tests for gene flow (based on the genome-wide single nucleotide polymorphisms, or SNP s), to thoroughly elucidate the species diversity of Diplocladon , based on a total of 53 specimens of Diplocladon assembled predominantly by passive collecting methods (flight interception trap and Malaise trap) from southern China. As a result, a total of 13 species are recognized from China, including nine new species, D. nigripes sp. nov., D. robustum sp. nov., D. nanlingense sp. nov., D. leigongshanense sp. nov., D. dinghuense sp. nov., D. hainanense sp. nov., D. zhuhaiense sp. nov., D. lutianense sp. nov. and D. jiulianshanense sp. nov. Our findings significantly enrich the species diversity of Diplocladon , and highlight the necessity of employing passive collecting methods and integrative taxonomy to uncover species diversity among taxa occurring in a limited range and facing challenges in resolving morphological ambiguities presented by paedomorphic beetles like Diplocladon .