Two new species of the diving beetle genus Liodessus Guignot, 1939 are described from high mountain regions in Venezuela: Liodessus meridensis sp. nov. from Laguna de Mucabají, Mérida and L. venezuelensis sp. nov. from Laguna de Mucabají and below Pico Bolívar, Mérida. We delineate the species using morphological characters such as male genital structure and beetle size, shape and color. Mitochondrial cox1 sequence data provided an additional character source. Both new species occur at altitudes above 3,500 m and were collected in shallow water at the edge of high-altitude ponds.

Dytiscidae, Liodessus, new species, Venezuela, Mérida

Liodessus Guignot, 1939 are small diving beetles, usually less than 3 mm long, and occur in the New World as well as the Afrotropical region (Biström 1988; Nilsson and Hájek 2021). In the high Andes, at altitudes from ca. 3,000 to nearly 5,000 meters, they are probably the most abundant aquatic beetles (Balke et al. 2020a; Balke et al. 2020b). However, diving beetles from such high altitudes of the Páramo and Puna regions remain poorly studied. Since 2019, eleven new species have been described from Peru (Balke et al. 2020a, b) and Colombia (Balke et al. 2020c; Balke et al. 2021; Megna et al. 2019). Since then, it has become apparent that many more remain to be discovered, most of them likely microendemics. To address this in a combined evidence framework, we established a DNA sequence-supported project for the study of these beetles (Balke et al. 2020a, b), using the Barcode of Life Data System (BOLD) of the Canadian Centre for DNA Barcoding and the 5’ mitochondrial cox1 gene fragment (www.boldsystems.org) (Ratnasingham and Hebert 2007). Here, we continue our collaborative research project on the water beetle fauna of the higher mountain regions of South America by reporting the discovery of two new species of Liodessus from Venezuela.

The following acronyms are used in the text: CBP (Collection D. T. Bilton, Plymouth, UK); MIZA (Museo del Instituto de Zoología Agrícola “Francisco Fernández Yépez”, Universidad Central de Venezuela, Maracay, Venezuela); SEMC (Natural History Museum and Biodiversity Research Center, University of Kansas) and ZSM (SNSB-Zoologische Staatssammlung, München, Germany, temporarily stored for further morphological work).

Morphological descriptions and photography. The description of morphological characters follows our previous work on Liodessus beetles, e.g. Balke et al. (2020b). Images were taken with a Canon EOS R camera. We used Mitutoyo 10× (habitus) or 20× (genital structures) ELWD Plan Apo objectives. These were attached to a Carl Zeiss Jena Sonnar 3.5/135 MC, used as a focus lens. Illumination was with three LED segments SN-1 from Stonemaster (https://www.stonemaster-onlineshop.de). Image stacks were generated with the Stackmaster macro rail (Stonemaster), and images were then assembled with the computer software Helicon Focus 4.77TM on an iMac with a Radeon Pro 5500 XT GPU.

DNA analysis. The DNA sequencing and data analysis protocols follow standard Canadian Centre for DNA Barcoding (CCDB) barcoding procedures (www.ccdb.ca). We delivered tissue samples to CCDB, which were processed and the barcode data uploaded to BOLD systems. We used a simple approach to calculate a neighbour-joining tree (p-distances) in Geneious software (version 11.0.4.), in order to learn if newly added entries could be assigned to existing species groups or not. This approach has been proven helpful in guiding the morphological descriptive process, not the least by enabling us to unambiguously identify the new species presented here, even in the absence of male specimens.

The two new species described here are the first high-altitude species of Liodessus reported from Venezuela, and we expect to discover additional species in the vast, unsampled Venezuelan mountain regions. Their phylogenetic position remains to be established based on a multigene dataset. Based on the single DNA fragment we utilized here, the two species are genetically well delineated from all other known high-altitude Liodessus. It is well understood that one genetic marker alone cannot be the ultimate tool for taxonomy (Dietz et al. 2021), in particular markers such as cox1, which are not involved in speciation per se (Kwong et al. 2012). Rather, such DNA sequence data can be used to guide the sorting of specimens to operational units and support the taxonomic decision-making process. This approach has been utilized successfully to study very diverse beetle taxa (Riedel et al. 2013a; Riedel et al. 2013b; Tänzler et al. 2012), including our own previous work on Liodessus. The approach can be technically scaled up massively, using next-generation sequencing technology, which also reduces analytical costs (Srivathsan et al. 2021; Wang et al. 2018). Such data do not, however, replace taxonomic expertise and the evaluation of morphological structure (Riedel et al. 2013a).

We are grateful for the generous support from the SNSB-Innovative scheme, funded by the Bayerisches Staatsministerium für Wissenschaft und Kunst (Project: 2018 „Geographische Isolation, Endemismus und Artbildungsprozesse bei Insekten in der hochmontanen Páramo Kolumbiens (und darüber hinaus)” as well as 2021 „The origin of the world’s widest altitudinal gradient“), and Bayerischer Pakt für Innovation (BayPFI) for digitizing equipment. Michael Balke acknowledges support from the EU SYNTHESYS program, projects FR-TAF 6972 and GB-TAF-6776, which helped preparing this research during type study visits to NHM and MNHN in 2017. We thank Andrew E.Z. Short for kindly providing specimens and advice for this study; he acknowledges support from the US National Science Foundation grant #DEB-0816904. Michael Balke acknowledges support from the Deutsche Forschungsgemeinschaft (BA2152/27-1). Adrián Villastrigo is a fellow of the Alexander von Humboldt Foundation, which enabled his participation in this research. Thanks to our colleagues at MIZA for hosting us in 2004.

Consortium of European Taxonomic Facilities (CETAF) data use statement: “Data on genetic material contained in this taxonomic article are published for non-commercial use only. Utilization by third parties for purposes other than non-commercial scientific research may infringe the conditions under which the genetic resources were originally accessed, and should not be undertaken without obtaining consent from the original provider of the genetic material.”