Benchmarking Springtail Recording

Recently, I've been thinking a lot about occupancy models for invertebrates. Other taxa, notably birds and butterflies (through the BTO Wetland Bird Survey and Butterfly Conservation's UK Butterfly Monitoring Scheme (UKBMS), respectively) have good negative data, i.e. an indication of where species are absent as well as where they are present. For most invertebrate taxa, partly because of lack of resource (recording effort) but mostly because of the inefficiency of recording (how can you be sure a springtail is absent from a particular area?), all we have are "White Holes" - gaps in the data which are difficult to interpret. This makes occupancy models difficult if not impossible to derive. The alternative is to fall back to benchmark species as indicators of recording coverage. Previously (Progress on the VC55 Springtail Atlas) I discussed the use of Orchesella cincta as a benchmark species for springtails. While the ubiquity of this species is a good reason to think that this is a valid choice, I've never actually tested the hypothesis - so here we go.

Heatmaps are pretty but inevitably focus attention on where the data is, rather than where it is missing. As an attempt to try to switch the emphasis I have used quadrat mapping - arbitrarily dividing VC55 into a grid and looking at the number of records within each section. A 25x25 grid worked but the the intervals were a bit small and a 10x10 grid is more informative (all VC55 Collembola records to end 2018):



The grid for Orchesella cincta looks like this:



To make sense of this, I converted the distributions into histograms:



These look pretty similar, but to be sure, I ran some further analysis:



There's a good correlation between the Orchesella cincta distribution and the overall Collembola dataset, and this is statistically significant (p = 2.2e-16). Thus Orchesella cincta is a good benchmark for springtail recording effort (at least in VC55). Phew!



Acknowledgements:
All data Copyright Leicestershire and Rutland Environmental Records Centre.
Data visualization performed using the R platform, v. 3.6.1 (R Core Team (2014) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org).
J. Cann for assistance with data visualization.

Springtails hitching rides on social insects

Fossil amber reveals springtails longstanding dispersal by social insects. (2019) BMC Evol Biol 19, 213 https://doi.org/10.1186/s12862-019-1529-6

Springtails (Collembola) are reported since the Lower Devonian and are thought to have originally been subterranean. The order Symphypleona is known since the early Cretaceous with genera distributed on every continent. This implies an ability to disperse over oceans, however symphypleonan Collembola have never been reported in marine water contrary to other springtail orders. Despite being highly widespread, modern springtails are rarely reported in any kind of biotic association. Interestingly, the fossil record has provided occasional occurrences of Symphypleona attached by the antennae onto the bodies of larger arthropods. Here we document the case of a ~ 16 Ma old fossil association: a winged termite and ant displaying not some, but 25 springtails attached or in close proximity to the body. By comparing the general constraints applying to the other wingless soil-dwelling arthropods known to disperse through phoresy, we suggest biases in the collection and observation of phoretic Symphypleona related to their reflexive detachment and infer that this behaviour continues today. The specific case of tree resin entrapment represents the (so far) only condition uncovering the phoretic dispersal mechanism of springtails - one of the oldest terrestrial arthropod lineages living today.

Isotoma viridis

In spite of all the rain and good numbers of springtails over the last few weeks (dominated by Dicyrtomina saundersi), Isotomids have been largely missing. However, the recent haul of leaf litter had good number of Isotoma viridis, a species I have not seen since last winter.

Return of some old friends

The springtails like the rain. I quite like the rain too, but maybe not this much. With the change in the season the springtails have changed. Some time ago I adopted Orchesella cincta as my index species for recording effort, on the basis that it is the commonest species in lowland Britain. Thus, when you don't see one specimen for six months, you begin to doubt. But now the season has changed they're back, and they're everywhere, and along with them are some old friends I haven't seen for a few months, Emtomobrya albocincta and E. multifasciata.

Springs Can Only Get Better

Monobella grassei.

I've got to admit not putting too much effort into springtail recording recently. Partly this is a hangover from the summer and partly it's because I've been busy with other things, but I do regularly record springtails when I'm out and recently it's become clear that what I think of as the "winter species" are here. Foremost among these is one of my favourites, Monobella grassei, which i've found several times recently.

I can't wait for the leaf litter season to kick off.

Recent Unusual UK Collembola Records

An update of the UK list which features two particularly notable additions. The first of these is Entomobrya intermedia, an extremely common species but not one which was not recognised by Steve Hopkin. Since we know know that it stands up under DNA, it has been formally added to the list. The other is the globally invasive Desoria trispinata, a species I have not yet recorded but seems to be spreading rapidly and needs to be on our radar.


Shaw, P., & Trewhella, S. (2019) Recent Unusual UK Collembola Records – Entomobryomorpha and Poduromorpha. British Journal of Entomology and Natural History, 32 (3) 217-230. https://pure.roehampton.ac.uk/portal/files/1192939/BJENH_Shaw19.pdf
Abstract: We report substantial updates to our understanding of the distribution of nine species of UK Collembola (orders Entomobryomorpha and Poduromorpha). We note four species omitted from the main UK key (one very common) and we note the rediscovery of five species in the UK after >50 years. Three of these were previously only collected in the UK by Richard Bagnall in the 1930s.
 

Progress on the VC55 Springtail Atlas

I have to admit that my springtail work has been on the back burner over the last month for a number of reasons. Summer is a good time to have a break and recharge the batteries, although the difference between the drought summer of 2018 and the wet August of 2019 is dramatic. What I have done recently is to take a look at the VC55 springtail records and do some data visualization using the R platform. Firstly, I mapped all previous VC55 springtail records (n = 560) to the end of 2018 (black squares) (all data copyright Leicestershire and Rutland Environmental Records Centre), then overlaid the records added in 2019 (blue triangles):


click for larger image

This is encouraging because although there are a few other people sporadically recording springtails in VC55, I have specifically targeted most of my efforts this year at extending the geographical coverage into new areas. This is particularly important because so much biological recording defaults to the regular honeypots. It is easy to see this by merging the dataset into a heatmap of observations:


click for larger image

I can make this a little more informative by breaking down the records into families and overlaying this on the heatmap:


click for larger image

The problem with this is that the data set (~600 records) just isn't large enough to say very much about the whole County, or to put it another way, the density of records is too low for good geographical coverage. In addition, there's another problem. I'm not aware of any systematic springtail recording which includes negative results, i.e. the absence of species as well as the presence. We know (anecdotally and from the heatmap) that recording effort is not equally distributed, but the limited dataset means that we simply don't have accurate geographical coverage. Resource limitations mean that there will probably never be widespread systematic recording of springtails, so my approach to this problem has been to adopt a benchmark species to infer recording effort. Orchesella cincta is said to be the most widely distributed species in lowland Britain, so I have adopted this to infer geographical coverage:


click for larger image

Thankfully (for my theory), the O. cincta data fits the heatmap pretty well, so validating this proxy for our atlas. What comes next is clearly getting off my backside and getting back out in the field :-)


Acknowledgements:

• All data Copyright Leicestershire and Rutland Environmental Records Centre.
• Data visualization performed using the R platform, v. 3.6.1 (R Core Team (2014) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org).
• J. Cann for assistance with data visualization.

Springtails in July

Pogonognathellus longicornis

Although July is pretty much the low point in the springtail calendar, the contrast between this year and last year is stark. While we've had the hottest ever day, we've also had plenty of rain and moderate temperatures. Out and about I've been finding springtails pretty much everywhere, recording the following species at the number of sites shown:

Entomobrya nivalis: 7
Deuterosminthurus pallipes: 4
Entomobrya nicoleti: 4
Orchesella cincta: 2
Entomobrya multifasciata: 1
Isotoma viridis: 1
Pogonognathellus longicornis: 1
Tomocerus minor: 1

Springtails about, but nothing of great interest. However, this has to count as a good July for springtails.

13.07.19 - Charnwood Lodge

Although Charnwood Lodge is the most heavily recorded site in VC55, I've only made one serious trip for springtails there previously, so it was past time to go back. There was a lot of the routine stuff I'm seeing everywhere at present - Deuterosminthurus pallipes, Pogonognathellus longicornis, Tomocerus minor. Notably, I also found a lot of juvenile Orchesella cincta, and some spanking new adults, a species I've not been seeing for the past few months now making a return:



The highlight of Charnwood Lodge is the acid heath, and grubbing around in the Sphagnum produced a number of Isotoma viridis, which although not unexpected, I think is a new species record for this site:

30.06.19 - Owston

In spite of temperatures over 30C the previous day, springtails were around in the damp bits of Owston. Dicyrtomina ornata reappears in its usual spot but Entomobrya nivalis remains by far the most prevalent species I'm seeing at the present time.

Prepare for lift off!

It is diagnostic of Pogonognathellus longicornis that this species is able to tightly curl both an4 and ant3 due to their flexible annular structure (c.f. Tomocerus, which is only able to curl ant4 slightly). Frans Jansens made the interesting comment on this photo that this individual is considering jumping and has curled ant4, presumably to avoid damage. This behaviour has not occurred to me before and I need to investigate this further next time I find some curly-wurlys to play with.

09.06.19 - Cribb's Meadow

Many springtails taking their summer break, but Deuterosminthurus pallipes and Entomobrya nivalis particularly abundant.

15.06.19 - Saddington Reservoir

A short collecting trip filling in a gap on the map. Clockwise from top left: Orchesella cincta, Entomobrya nicoleti, Entomobrya nivalis, Pogonognathellus longicornis.

Willowsia

There are two confirmed species of Willowsia in the UK. They resemble shiny, iridescent Entomobrya.

Willowsia platani is an aerial species resistant to desiccation and is found on trees and in buildings. This species has a variable pattern of pigmented bands and spots on the dorsal side (some specimens are much paler than those shown here):





Willowsia platani has characteristic leaf-shaped scales:



The mucro has two teeth and there is a spatulate tenant seta:



The empodium is about two-thirds the length of the claw:




In contrast, Willowsia buski is a plainer-looking species. The scales are a different shape, more triangular then W. platani. Photo by Philippe Garcelon:

Springtails of the North

I have to admit to still not putting too much effort into springtails recently. Although we've had rain now the ground is still very dry and unproductive so all samples have come from sweeping or beating vegetation. I sampled a couple of sites near Croxton Kerrial and also at charley on Charnwood. I didn't find anything very exciting but Deuterosminthurus pallipes is by far the most frequent species at the moment. Every one of the hundreds I have found have been the yellow form - I've still only ever found a single specimen of the purple nominate form.

Big trouble in Lepidocyrtus

"Everything is everywhere but the environment selects"

Early in the twentieth century the Dutch microbiologists Beijerinck and Becking proposed the hypothesis that "Everything is everywhere but the environment selects" to explain the distribution of microorganisms. This has been much debated but it makes a lot of sense for highly mobile organisms that can be blown on the wind. At what scale it stops being true is unclear, but ecological determinism means that for all species, the environment selects which species persist. One of the most important factors in selection is climate, which determines the current distribution of species and will determine how these change in the future. The flora and fauna of Britain bear the signs of restriction by and subsequent repopulation following the last ice age. Not much survived under the ice cap but there were geothermal islands and not all of the UK was glaciated. The inability of springtails to fly limits their spread and repopulation when the ice retreats but their small size and abundance means that they are able to persist in suitable niches in otherwise adverse environments. Thus the present day distribution of springtails carries the historical signature of climate change. A recent paper examines two genera of springtails, Entomobrya and Lepidocyrtus, and reveals not only the impact of glaciation but also present day relationships (Faria, Shaw & Emerson, 2019).

Springtail samples were collected from 98 sites across Britain and the DNA sequence of a region of the mitochondrial cytochrome oxidase I gene determined and used to establish relationships. The patterns revealed indicate both geographical and genetic relationships in these two genera. Analaysis identified 12 Operational Taxonomic Units (genetic groupings) for Entomobrya and 18 for Lepidocyrtus in Great Britain. Lepidocyrtus richness was significantly lower in glaciated than unglaciated areas, whereas there was no difference for Entomobrya richness. The data reveal evidence for population persistence of Entomobrya (some of our most familiar springtails) OTUs within Great Britain, estimated to extend back at least some 77,000 years.

For me however, the most interesting aspect of this paper is what it says about present day species. For the most part, the recognised UK Entomobrya species (albocincta, intermedia, marginata, multifasciata, nicoleti, nivalis) behave themselves - colour‐pattern morphospecies were generally monophyletic but concealed two or more mtDNA OTUs. However, the correspondence between morphospecies and OTU was less clear for UK Lepidocyrtus species (curvicollis, cyaneus, lanuginosus, lignorum, ruber, violaceus) - 6 morphospecies harbour 18 distinct OTUs. Specimens assigned to the morphospecies Lepidocyrtus cyaneus featured in seven OTUs, and the dominant OTU contained a mix of morphospecies (mainly L. lignorum and L. lanuginosus). Unexpectedly high cryptic species diversity has been noted previously in this genus and together these results suggest that key taxonomic features (mainly distribution of scales, ground colour) may be unreliable indicators of species boundaries. How exactly the genetic diversity of UK Lepidocyrtus species translates into physical variability is unclear, but may go some way to explain the length of time I often spend scratching my head when examining Lepidocyrtus specimens...
 

In response to my enquires, Frans Janssens commented:  

Do not confuse OTU's with species. A species *can* map to several OTU's. ... The fact that "the dominant OTU contained a mix of morphospecies (mainly L. lignorum and L. lanuginosus)" suggests errors have been made in species identification of the specimens, given both species are easily distinguished based on morphology. Example: the specimens IDed as lanuginosus possibly were lignorum specimens with aberration in scale position on legs: such as specimens that lost all scales on legs during specimen handling. Please continue to record Lepidocyrtus based on morphology.

Matthew Shepherd also left an interesting comment: 

"It's not just Lepidocyrtus - many soil animals, especially those with parthenogenesis (females giving birth to more clone females without fertilisation), don't really fit into the concept of a species... One of our commonest mites worldwide, Platynothrus peltifer, has been shown by Alfried Vogler and co-workers to have evolved into 12 global clades whose genes suggest that this species has been reproducing in this way, producing morphologically identical creatures, since the death of the dinosaurs. A 60 million year old species that is effectively actually just one cloned individual! I think that we can still learn a lot from lumping these morpho-types together for recording purposes, whether they're clusters of radiating species or ancient clones. It's still valid and ecologically useful to record brambles, dandelions and eyebrights, even though these are radiating aggregations of species. I think that we will have to just be a bit flexible with the data when we come to analyse it."

  

O’Malley, M.A. (2008) ‘Everything is everywhere: but the environment selects’: ubiquitous distribution and ecological determinism in microbial biogeography. Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences, 39(3), 314-325. https://www.sciencedirect.com/science/article/pii/S136984860800040X

Faria CMA, Shaw P, Emerson BC. (2019) Evidence for the Pleistocene persistence of Collembola in Great Britain. J Biogeogr. 46: 1–15. https://doi.org/10.1111/jbi.13610
Abstract: Using two genera of springtail, Lepidocyrtus and Entomobrya (Collembola), we test for genetic signatures of Pleistocene persistence of soil arthropods in Great Britain. A region of the mitochondrial cytochrome oxidase I (COI) gene was sequenced for 1,150 Collembola specimens from the genera Lepidocyrtus and Entomobrya across Great Britain. Individuals were clustered into Operational Taxonomic Units (OTUs), and both OTU richness and geographical patterns of genetic variation within OTUs were compared between glaciated and unglaciated areas to identify signatures of OTU persistence through Pleistocene glacial events. Our analyses identified 12 Entomobrya and 18 Lepidocyrtus OTUs in Great Britain. Lepidocyrtus OTU richness was significantly lower in glaciated than unglaciated areas, whereas there was no difference for Entomobrya OTU richness. However, both genera presented clear patterns of geographically disjunct genetic variation and geographically localized diversification of OTUs. Estimated dates for the onset of in situ diversification events indicate population persistence that pre‐dates the Last Glacial Maximum. Patterns of genetic diversity within Collembola OTUs in Great Britain add to a growing body of evidence that elements of the invertebrate fauna have persisted in situ through Pleistocene glacial cycles. Genetic signatures of population persistence in more northern glaciated areas of Great Britain support a hypothesis of geothermal glacial refugia that call for further investigation with other soil mesofaunal taxa.

The Pitfalls of Springtails

For the past few weeks I have been running a pitfall trap in my garden. This is more of an experiment than a serious attempt at systematic recording but one observation has struck me as interesting. I started during a very dry period and at first only found Lepidocyrtus cyaneus and Orchesella cincta. After a week it rained and Tomocerus minor turned up in good numbers, and has remained present every day since. Although it is now raining quite regularly, on one day only there were quite a few Isotomurus unifasciatus in the trap, but they have never reappeared again. Of course, I am only running one trap, but the variability of recovery has been quite surprising - you would need to run quite a number of traps over quite a long period to accurately establish what species were present in a location.

The tale of the wonky Orchesella cincta

A single Orchesella cincta from the pitfall trap. The wonky antennae could be due to a number of reasons, but I'd bet my money on an encounter with a predator, during which many springtails are happy to regard antennae as "optional extras", useful though they are. Springtails are on the menu for pretty much every carnivorous or omnivorous species out there (although I haven't tried them myself yet - I bet they taste like chicken). Frustrating though this may be for springtails fans it's probably a good thing. Being knee deep in springtails would be a rather itchy experience. Those scales get everywhere.

The Drought

Pogonognathellus.

I've got to admit I've been slacking off with the springtails over the last couple of months. The drought started it off, but now we've had rain and the summer species are here. I need to get my act together again but the summer holiday feeling persists. A little break will do me good and I plan to do some pitfall trapping soon.

The pitfalls of studying springtails

To get a complete picture of the springtails in an area it's necessary to combine various collection methods, including pitfall trapping. This is not something I have done before but I have been running a pitfall trap for a few days. It collects a wide variety of taxa but since I'm running a dry trap the organisms I don't think I can identify are returned to run free without harm. Several springtails species have turned up so far, including numerous specimens of small (~1mm) Lepidocyrtus. I struggled to identify these until I eventually figured out that they are Lepidocyrtus cyaneus, seemingly the predominant species at present on my collecting site.

06.05.19 - Highway Spinney

Did a bit of surveying on a new patch. Very dry and not too much found but I did turn up Entomobrya albocincta, Entomobrya nicoleti and Entomobrya nivalis.

02.05.19 - Stoney Stanton

I was asked to participate in a farm survey covering all taxa. Although conditions were very dry I took the opportunity to look for springtails. There were reasonable numbers of Entomobrya multifasciata and Entomobrya nicoleti but by far the most numerous were Deuterosminthurus pallipes. For the first time ever, I found the purple nominate form - outnumbered at least 100:1 by the yellow form repandus.

17.04.19 - Croft Pasture

With the dry conditions I headed for the water meadows at Croft desperate to find moisture (and springtails). Both were in short supply but I found a few Entomobrya nicoleti and Entomobrya nivalis. Most notable were the Deuterosminthurus pallipes - a sure sign that summer's here (even if the temperatures still feel like winter).

10.04.19 - Tilton Cutting

I visited Tilton Cutting because at times it's so wet that you can't really go there. However, the drought is really beginning to bite and finding any springtails at all was hard work. Eventually I managed to scrape together a short list: Entomobrya nivalis, Orchesella cincta, Pogonognathellus longicornis, Tomocerus minor.

06.04.19 - Swadlincote

Clockwise: Entomobrya albocincta, Entomobrya nivalis, Vertagopus arboreus.


Not many springtails from the National Forest so we trekked up to Pick Triangle at Swadlincote to put some dots on the map. Unfortunately it turned out to be hard work because it was so dry. At Albert Village lake I managed to find one single specimen, a Tomocerus which I managed to lose. Across the road at Pick Triangle we did a little better beating vegetation, but this site needs another visit at a more suitable time of year.

30.03.19 - Pickworth Great Wood

(not to scale)


We trekked all the way over to Pickworth for two reasons, first because it is a biologically rich area which is seriously under recorded, and second to put dots on the atlas - it's as far east as you can go without being in Lincolnshire. Indeed on entering the wood you can stand with one foot in VC55 and the other in VC53 (selfie temptation resisted). And on entering the wood virtually the first thing we saw was an Orange Underwing (Archiearis parthenias). The Lepidoptera were spectacular - by the end of the day though we'd seen dozens of Orange Undwerwings (I stopped counting at 20) plus too many Brimstone and Peacock butterflies to count, three Commas and two male Orange Tips. It was hot and sweaty and I got sunburnt because I had not adjusted my headgear from winter (wooly) to summer (floppy). However, butterfly weather is not springtail weather, and the dry, cracked soil put a crimp in springtails recording, although we found many of the usual suspects. Pickworth is on the list for return visits in more favourable conditions.

Reservoir 13

There aren't many books about springtails around, and there are even fewer novels featuring springtails. Reservoir 13 by Jon McGregor is not only the best book I've read for a long time, it's also the only novel I've read where springtails get plenty of mentions. Are there any others?

27.03.17 - John O'Gaunt

I headed up to John O'Gaunt to do some recording because it was a big blank area on the VC55 Springtail Atlas. However I had two problems on this trip. The first was that this entire area is heavily agricultural with poor diversity, but the major problem was the lack of rainfall. At the end of March in what should be peak springtail season the soil was dry and cracked and springtails were hard to find. In the end I sampled as close to the water as possible in Gaddesby Brook (and also in a damp drainage ditch by the viaduct, where I found nothing). The banks of the brook turned up Entomobrya nicoleti, Entomobrya nivalis, Isotoma viridis and Orchesella cincta, but perhaps the most notable species were a number of Entomobrya albocincta, which seems to be quite prevalent at the moment and is normally less abundant:

24.03.19 - Ulverscroft

Ulverscroft is one of my favourite sites and although well recorded, because it was a nice spring day we opted for a wander though the woods. No surprises but a nice day out:

20.03.19 - A bit of excitement at Thornton

I received a tip-off that there was a big bloom of springtails at Thornton Reservoir. Because of the low rainfall over the winter water levels were very low and springtail numbers had exploded on the exposed mud. Unfortunately I was not able to get there quickly, and the following week was mostly gales, falling trees and torrential rain so by the time I did get on site the water level had risen several feet and most of the mud was underwater. However, there were still good numbers of Isotomids under rock by the waterline. These turned out to be Isotomurus palustris sensu lato - near continuous dorsal line and fainter lines on the sides of the abdomen (juveniles paler); mucro with four teeth, apical tooth smaller than the others and no lateral seta:




Also present were large numbers of Paranchus albipes. This is an interesting beetle which is very much a water line specialist, following the water level up and down. It's also one of the specialist springtail predators, numbers having exploded based on the food supply:




Because it was a nice day I took a walk around the reservoir and sampled under the bark of a Scots Pine as well as from Ivy growing up trunk because this was a good contrast to the mad at the waterline at the other end of the reservoir. Nothing surprising here, lots of Entomobrya nivalis, but also probably more Entomobrya albocincta than I have seen in a sample:


Entomobrya albocincta


Entomobrya nivalis

PlaqSearch

A few years ago when I was pretending to be a mycologist I became aware that the community was using PlaqSearch (Google it: stated ingredients: Fd and C Blue No 1, D and C Red No 28, Dextrates, Magnesium Sterate, Sodium Starch Glycolate) for differential staining of fungi. This is designed to show if you have dental plaque so it is safe to use as it is intended for oral use. In fungi, some tissues stain blue and others pink. I still have a bottle of this kicking around in my microscope kit and every time I make slides I think "I should try it on springtails". And so I did.

My first attempt was on Isotoma viridis preserved in 70% alcohol - a 5 minute stain, destain in water and mount. The results were underwhelming, just a few random pink patches resulting from inefficient destaining I think. In retrospect, since PlaqSearch is water-based this was predictable because of the hydrophobic nature of the Collembolan cuticle:



I had another go, this time with a cleared specimen:



Nothing really of interest, so I conclude that PlaqSearch doesn't offer anything of interest to the Collembologist (if that's a word).