Another instance of DNA not helping

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. 

 

Finally some good news

2024 was a very sad year when we lost some major figures in the springtail community. Frans Janssens was an enormous help to me when I started recording springtails and I was sad to hear of his passing. I also learned so much from Peter Shaw that I felt this additional loss keenly. Fortunately, 2025 begins on a brighter note with the news that James McCulloch has taken over the UK Springtail Recording Scheme. James is a highly knowledgeable springtail enthusiast, and even better, has already started verifying springtail records submitted via iRecord, a daunting task which has not happened before. All this is very positive for the future and I am encouraged by this positive development. 

 

Sminthurides malmgreni

For the past ten years the aquarium housing my ancient Axolotl has also been home to a colony of Sminthurides malmgreni. I have done nothing to maintain them, but they happily persist wandering around on the surface of the water, on and off the 1.5mm long leaves of the Common Duckweed, Lemna minor. 

Inevitably on Springwatch, someone gets shipped off to Scotland to be eaten alive by midges and film the Red Deer stags locking antlers during the rut. If I want to watch rutting, I have no need to move further than the corner of my study, where the emancipated females lift the smaller males off their feet and wander off with them whenever they feel the urge. 

 

A Rare Springtail?

 

Into the darkness

I've been playing with darkfield microscopy - poor man's phase contrast. Darkfield uses obliqe illumination as a cheap optical trick to increase the contrast of transparent and traslucent specimens. It can produce dramatic images with dark backgrounds and usually features prominently in microscope photography competitions such as Nikon's Small Worlds. I started out with the somewhat translucent furca of a handy Isotomurus unifasciatus specimen. On the left is my conventional setup of top plus bottom illumination, post processed; on the right darkfield transillumination, both stacked with Zerene: 

The problem here is that inserting the darkfield disc into the light path lengthens the exposure time 20-fold and the image quality suffers as a result. Looking at the non-transparent abdomen of the same specimen (conventional illumination):

Darkfield plus supplemental top light:

I think this is the better result, but clearly I need to find some transparent specimens to get maximum benefit from darkfield. 

 

Sminthurus viridis ssp. cinereoviridis

I have to admit that springtails have been on the back burner recently while I've been focusing mostly on spiders. The weather hasn't helped but it's not an excuse, mostly I've been working on spiders. I have been recording springtails regularly, but I haven't posted anything publicly because I haven't found anything particularly interesting - until today. This morning the vacuum sampler turned up a whole bunch of these. After some rusty fumbling, they keyed out to be Sminthurus viridis (which I have found several times recently), but specifically Sminthurus viridis ssp. cinereoviridis (thanks to Frans Janssens for help with the I.D.).

Sminthurus viridis ssp. cinereoviridis has 2 spots on small abdomen. In the ecovariant nigromaculatus of S. viridis, 3 spots are present: https://www.collembola.org/images/stach/1956/Sminthurus-viridis-1956-J-Stach-Poland-PlateXXXII-Fig3.jpg There are supposedly difference in chaetotaxy of the setae on the subcoxa of the third leg, but I have found it impossible to image these. Steve Hopkins was reluctant to accept nigromaculatus as a separate species. As a dyed-in-the-wool taxonomic lumper, I wouldn't disagree. Frans Janssens calls it "Sminthurus viridis (ecovariant nigromaculatus)", which is said to be associated with sandy areas, heathland, moors, heather, etc. My specimens came from the wettest of wet water meadows alongside the River Soar and have 2 abdominal spots, so Sminthurus viridis ssp. cinereoviridis it is.

Before The Rains

A cautionary tale

For those who think they can tell Isotoma viridis from other Isotoma by the colour alone - two Isotoma viridis specimens from the same sample, one green, one not, confirmed by the manubrial teeth.

Some like it wet

I recently bought myself a G-vac - for the uninitiated, a cordless garden leaf vacuum adapted for use as a bug vac - and I took it for its second outing this morning. How do you convert a leaf vacuum to a bug vac? Well essentially you tape a net bag over the mouth of the inlet tube. On a recommendation from a more experienced bug-vaccer I bought a nylon jam strainer bag to use for this (others use net curtain material). Now I will admit that the primary reason I bought the bug-vac was for spider work, and I wan't at all sure the jam strainer bag would retain insects as small as springtails, but on its first outing a couple of days ago I was delighted to find it worked with large spiders all the way down to springtails, including the little ones such as Lepidocyrtus.

A week or so ago, pre-vac, I had done some sampling in wet meadows beside the River Soar. At that time I'd spotted a patch of Juncus sitting in a damp hollow that looked interesting but I didn't have time to go there on my first visit. This morning I decided to go back and take a look, this time armed with the bug-vac. Bearing in mind this is a piece of electrical equipment, albeit double insulated to EU standards and designed to suck up wet leaves, I'm pretty cautious about mixing electricity and water because the 36V battery in the bug-vac could give out quite a jolt. I was therefore a bit alarmed that the bug-vac started spitting water out of the inlet when I stuck it in the Juncus, but the point of all this dicing with death is that the bug-vac turned up (alongside more run of the mill species) my first ever Isotomurus plumosus in VC55. I'm delighted but I won't be pushing my luck too far.