Five years ago I had a crisis of confidence when Peter Shaw published his paper on DNA analysis of Lepidocyrtus - see: Big trouble in Lepidocyrtus. DNA analysis made identification of Lepidocyrtus much worse rather than helping! While I was trying to find my way through the mess, Matthew Shepherd commented "many soil animals ... don't really fit into the concept of a species", but went on to say "we can still learn a lot from lumping these morpho-types together for recording purposes". Frans Janssens commented "please continue to record ... based on morphology". Nevertheless I had lost a lot of confidence and so put Springtails on the back burner.
Recently I worked up the courage to dip my toe in the DNA bathwater again. The Barcode of Life Data Systems (BOLD) project aims to derive taxonomic information from DNA barcodes: https://bench.boldsystems.org From the BOLD website I obtained a useful result which supported the idea that some questionable Hemiptera morphotypes do indeed seem to be distinct species. Encouraged, I decided to go back to BOLD and try to figure out what I could derive for two of the most problematic Collembola groups.
Species identification in Isotomurus is problematic because it relies on variable dorsal pigmentation patterns. In conversation Peter Shaw told me that he was planning DNA work on Isotomurus with an aim to review the genus, but sadly that didn't happen. Isotomurus records on BOLD currently consist of 727 records forming 43 BINs (clusters). (The Barcode Index Number System (BINs) clusters barcode sequences algorithmically. Since clusters show high concordance with species, this system can be used to verify species identifications as well as document diversity when taxonomic information is lacking.) A number of the Isotomurus BINs consist of single sequences representing unknown "species". BOLD lists 34 Isotomurus "species". DNA demarcation lines (BOLD BINs) and pigmentation patterns do not fully align. This doesn't really help me but at least it clarifies what the problem is - it's daft to identify morphospecies based on a single variable character such as pigmentation.
So far, so bad, but I also wanted to look at another problematic group, the Katiannidae (which includes Sminthurinus). Here BOLD has 5,250 records forming 294 BINs (clusters), with 51 "species" recognized by BOLD. It's widely acknowledged that the family Katiannidae is a mess and needs revision, but then I stumbled across a paper that I've been ignoring during my Collembola sabbatical:
van Bezouw, R. F., McCulloch, J., Janssens, F., & Berg, M. P. (2022). An emended description of Sminthurinus lawrencei Gisin 1963, with notes on the identification of black Sminthurinus species. Soil Organisms, 94(3), 127-138. https://doi.org/10.25674/so94iss3id283
The great thing about this paper is that it uses a precise character (chaetotaxy - position and number of setae (hairs) on the dentes), rather than a variable one like pigmentation, to define morphospecies. While chaetotaxy is not a useful field characteristic, the paper also claims that macrophotography can be used to separate the black Sminthurinus species. While I'm not ready to go back to Isotomurus, it might be time to pay Sminthurinus some attention again.
