Every Single Specimen Counts: A New Docosia Winnertz (Diptera: Mycetophilidae) Species Described from a Singleton

Singleton-based species names and fungal rarity: Does the number really matter?

Fungi are among the least known organisms on earth, with an estimated number of species between 1.5 and 10 million. This number is expected to be refined, especially with increasing knowledge about microfungi in undersampled habitats and increasing amounts of data derived from environmental DNA sequencing. A significant proportion of newly generated sequences fail to match with already named species, and thus represent what has been referred to as fungal "dark taxa". Due to the challenges associated with observing, identifying, and preserving sporophores, many macro- and microfungal species are only known from a single collection, specimen, isolate, and/or sequence-a singleton. Mycologists are consequently used to working with "rare" sequences and specimens. However, rarity and singleton phenomena lack consideration and valorization in fungal studies. In particular, the practice of publishing new fungal species names based on a single specimen remains a cause of debate. Here, we provide some elements of reflection on this issue in the light of the specificities of the fungal kingdom and global change context. If multiple independent sources of data support the existence of a new taxon, we encourage mycologists to proceed with formal description, irrespective of the number of specimens at hand. Although the description of singleton-based species may not be considered best practice, it does represent responsible science in the light of closing the Linnean biodiversity shortfall.

Current State of DNA Barcoding of Sciaroidea (Diptera)-Highlighting the Need to Build the Reference Library

DNA barcoding has tremendous potential for advancing species knowledge for many diverse groups of insects, potentially paving way for machine identification and semi-automated monitoring of whole insect faunas. Here, I review the current state of DNA barcoding of the superfamily Sciaroidea (Diptera), a diverse group consisting of eight understudied fly families where the described species in the world makes up some 10% (≈16,000 species) of all Diptera. World data of Sciaroidea were extracted from the Barcode of Life online database BoldSystems (BOLD) and contrasted with results and experiences from a Nordic project to build the reference library. Well over 1.2 million (1,224,877) Sciaroidea specimens have been submitted for barcoding, giving barcode-compliant sequences resulting in 56,648 so-called barcode index numbers (BINs, machine-generated proxies for species). Although the BINs on BOLD already represent 3.5 times the number of described species, merely some 2850 named species (described or interim names, 5% of the BINs) currently have been assigned a BIN. The other 95% remain as dark taxa figuring in many frontier publications as statistics representing proxies for species diversity within a family. In the Nordic region, however, substantial progress has been made towards building a complete reference library, currently making up 55% of all named Sciaroidea BINs on BOLD. Another major source (31%) of named Sciaroidea BINs on BOLD comes from COI sequences mined from GenBank, generated through phylogenetic and integrative studies outside of BOLD. Building a quality reference library for understudied insects such as Sciaroidea requires heavy investment, both pre sequence and post sequence, by trained taxonomists to build and curate voucher collections, to continually improve the quality of the data and describe new species. Only when the BINs are properly calibrated by a rigorously quality-checked reference library can the great potential of both classical taxonomic barcoding, metabarcoding, and eDNA ecology be realized.