25.01.19 - Great Glen

A quick but very productive Burns Night trip down to Great Glen to fill in an empty tetrad.

Top row: Dicyrtomina ornata, Dicyrtomina minuta, Monobella grassei
Bottom row: Entomobrya intermedia, Orchesella cincta, Orchesella villosa




The big surprise on this trip was a single dark Dicyrtomina specimen with a solid patch of dark pigment at the posterior end of the abdomen similar to Dicyrtomina ornata, but unlike D. ornata the abdomen has an entirely purple ground colour with lighter orange reticulations. The head is lighter than the body, whereas in Dicyrtoma fusca the colour of the head is similar to the body. This seems to be a specimen of Dicyrtomina violacea, one of very few records from the UK:

19.01.19 - Kilby

On a very cold morning with the wind blowing straight from the Urals, I didn't fancy much more than a quick collecting trip so I consulted the map and decided that a short drive down to Kilby would fill in another tetrad. I grabbed a bag of leaf litter and was home again inside the hour, where, heating on, I sorted through it in the warm. It proved to be very productive, with Dicyrtomina saundersi, Entomobrya intermedia, Entomobrya nicoleti, Orchesella cincta, Orchesella villosa and Pogonognathellus longicornis all present. However, the main feature was a large number of very green isotomids:



The natural assumption was to assume that these were all Isotoma viridis, but I checked half a dozen of them and they were all Isotoma caerulea (two pairs of manubrial teeth plus dorsal macrosetae on manubrium A<B). This confirms my recent experience that it is not possible to distinguish between Isotoma anglicana/caerulea/viridis by habitus (general appearance) and that microscopic confirmation is required:




In amongst all the caerulea were two isotomids with a dark median band. Identifying these was a bit tricky as they had lost their macrosetae, but they turned out to be Isotomurus pseudopalustris (two characteristic pale dots either side of midline on abd4):

12.01.19 - Church Langton

Another foray into the Lutterworth Triangle. A bag of leaf litter yielded a single Entomobrya nicoleti, a few Orchesella villosa and lots of Dicyrtomina saundersi. Also present were quite a few Isotomids. At first sight, it would have been easy to put these all down as Isotoma viridis, but examination of the manubrial teeth revealed two pairs, meaning that all these specimens were actually Isotoma anglicana or Isotoma caerulea (not determined):


click for larger image

Springtail Phenology

Phenology is the study of the periodic (seasonal) cycles of living organisms. I used the NatureSpot dataset to 31.12.18) to look at the phenology of springtails in VC55:


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The criterion for inclusion was a minimum of at least 10 verified records. I don't think there are too many surprises here, but I am pleased to see that Orchesella cincta seems to hold up as a good benchmark species, pretty accurately reflecting the overall variation, although Entomobrya intermedia is the only species with records for all 12 months.

What this clearly needs is a much larger dataset, which will undoubtedly provide both a wider range of species and more significant numbers. A task to revisit in a year's time. The other issue to consider is normalising recording effort. I'm unsure of the best way to do this but perhaps considering the number of recording sessions per month, defined as unique site-date combinations, is a possible proxy.

Close Encounter

Like most simple organisms, springtail behaviour runs on a pretty simple algorithm:

1. Can it eat me?
2. Can I eat it?
3. Can I make love to it?

Here Orchesella cincta meets Tomocerus minor. Unusually, they didn't immediately spring away from each other but spent some time checking the other out. They both seem to be juveniles so I guess it's teenage experimentation.

"May contain horse” - springtails and DNA

Cann, AJ (2019) "May contain horse” - springtails and DNA. Leicestershire Entomological Society Newsletter, 60: 5-6.

Click for larger image:

The Springtails of Leicestershire and Rutland

Cann, AJ (2019) The Springtails of Leicestershire and Rutland. Natural History Section Newsletter, Leicester Literary & Philosophical Society, Spring 2019.

Click for larger images:

Isotoma are like busses

You wait ages for Isotoma anglicana to come along and then, when you're desperate to find some Isotoma viridis so you can make comparison images of the manubrial teeth, it's anglicana all the way down...

What do these manubrial teeth do? They hook onto the teeth on the rami of the hamula or retinaculum, a catch-like structure which holds the springloaded furca in place under the body. In most other species of Collembola the retinacular teeth hook onto ridges at the inner base of the dentes. Since this is a lock and key type mechanism, the shape and arrangement of teeth varies from one species to another.

05.01.19 - Gilmorton - Mottes and Moats

We celebrated our impending return to work (!) by a quick trip down to Gilmorton. In spite of constant grey skies and not having seen the sun for days, the ground was quite dry and at first, with the leaf litter all crispy, I began to think we wouldn't find much. But Gilmorton has a secret weapon - a Norman motte surrounded by a moat. Technically the moat is dried up (apart from a section which has been turned into a garden pond), but that's dried up in the sense of not actually underwater - it was quite squishy in the bottom and full of Sweet Chestnut leaves. Immediately we began to find springtails, notably quite a few Dicyrtomina minuta, which shone out in the gloom:



However, what caught my eye were lots of Isotomids. When I got these home for a closer look most of them looked like Isotoma viridis, and indeed that's what they turned out to be under the microscope, with a single tooth on the apical edge of the manubrium:



However, several specimens were larger and much darker that the "normal looking" I. viridis in the sample and I strongly suspected these might be Isotoma anglicana:



I spent a long time working on these but because of my lack of microcopy skills I was not able to confirm these as anglicana because I couldn't see any definite evidence of two manubrial teeth, so reluctantly, I had to put these down as one of the ones that got away. I am very cautious of confirming the identity of the Isotoma anglicana/viridis species pair because we know that these have been so frequently confused in the past.




Also present on the site at the bottom of a big leaf pile which was nice and damp at the bottom were Dicyrtomina saundersi, Orchesella villosa and Pogonognathellus longicornis (but no Orchesella cincta). All in all, probably the best afternoon I've ever spent grubbing around in the bottom of a Norman moat (n=1).

03.01.19 Gumley - Putting Squares in the Triangle

My first recording trip of 2019 was to cover a tetrad in the infamous Lutterworth Triangle (Lutterworth - Market Harborough - Leicester), the place where biological recording disappears. I settled on Gumley but frankly we could have gone anywhere as this is such a recording desert. We did a pleasant circular walk around the village and came home with two bags of leaf litter, which proved to be very productive. I was able to make my second county record of Monobella grassei, always a welcome sight:



I'm now always pleased to find Orchesella cincta since this is now one of my recording benchmarks. I also found a couple of Orchesella villosa, abundant Dicyrtomina saundersi, and several Entomobrya nicoleti and Lepidocyrtus lignorum:

Clearing Springtails

Clearing insect specimens is commonly performed to help visualize fine structures under the microscope. Various reagents have been used for this purpose, one of the most widely used being chloral hydrate, a component of Hoyer's mounting medium used for small arthropods such as springtails and of Melzer's reagent for fungi. Chloral hydrate is a hypnotic substance which has been used as a date rape drug, accordingly, it is a controlled substance and difficult to obtain. A more viable alternative is the use of alkaline solutions such as sodium or potassium hydroxide to clear cuticle pigmentation and make external features more clearly visible.

Isotoma anglicana/caerula and Isotoma viridis can only be distinguished by examining the number of teeth on the dorsal apical edge of the manubrium (Isotoma anglicana has two teeth on each side, Isotoma viridis has one). It is not essential to clear the specimen to do this, but depigmentation usually makes the teeth much easier to see.

Isotoma anglicana/caerula, pigmented specimens:



Isotoma anglicana/caerula, cleared specimen:




Clearing Method:
Make a solution of 10% sodium hydroxide (NaOH) (careful, this is caustic).
Transfer the specimen to a small, sealed tube containing approximately 0.1 mL of the alkaline solution.
Float the tube on hot water for 5-15 minutes (you may need to experiment to find the optimum time).
Transfer the specimen into a drop of plain water on a microscope slide and cover with a glass coverslip.
Examine under the microscope.

The first time you do this it may seem off-putting or too complex to bother with, but if you have a supply of specimens to practice on, it soon becomes fairly easy, although if you're as ham-fisted as me you will ruin the odd specimen, so it helps to have more than one! On a number of occasions I have accidentally pinged a specimen across the room while transferring it from tube to slide - good luck finding it on the carpet!

Family Isotomidae

Isotomid characteristics:

• unscaled
• elongated body and body segments of approximately equal length (c.f. Entomobryidae, abd4 more than twice as long as abd3)
• antennae with 4 segments of similar length
• 8+8 ocelli
• furca & PAO present
• no anal spines

The presence and positioning of macrosetae (long hairs) and bothriotricha (mechanoreceptive hairs) are important in separating these genera. However, these are easily lost and may be missing. In this case you have to check whether or not empty sockets of macrosetae are present on the skin surface (difficult). Bothriotricha are often difficult to see even if present, but the pits in which they sit may be visible.

Ocelli:


Desoria - covered in short setae (hairs); ocelli B-D-E in straight line; mucro has four teeth but does not possess a lateral seta, apical tooth is large (c.f. Isotomurus); no teeth on manubrium (c.f. Isotoma); Hopkin key #224

Isotoma - long macrosetae on all body segments; ocelli C-D-E in straight line; mucro has three teeth; bothriotricha absent; Hopkin key #220

Isotomurus - long macrosetae on abd4-6 only; ocelli B-D-E in straight line; mucro has four teeth, apical tooth smaller than the others (c.f. Desoria); bothriotricha present; Hopkin key #209 (pigmentation patterns).

Vertagopus - no long macrosetae but a fuzzy cover of short setae; mucro has four teeth; tibiotarsi (adjacent to claws) have clavate tenant (knobbed) setae; only two British species; Hopkin key #215

31.12.18 - Market Bosworth Square Bashing

My New Year Resolution was to get more organized by covering non-recorded tetrads, and I finished the year by getting a jump start on this plan. Previously, there were no Collembola records at all from this area so I came home with two bags of leaf litter to see what I could find.

On a pile of Birch logs I could see plenty of springtails crawling around, but I couldn't see what they were until I got a few home, when they turned out to be a mixture of Entomobrya nivalis and Vertagopus arboreus:



After that I was sampling leaf litter, which turned up the inevitable Dicyrtomina saundersi, Orchesella cincta (yay, another tetrad benchmarked!), and a single Orchesella villosa juvenile. There were also lots of pale Lepidocyrtus. I spent a while looking for setae on the head to try to identify these by chaetotaxy, but being honest, I couldn't see any evidence of setae at all, let along intraocular ones. However, what I could see were scales on Ant1, meaning that these must be Lepidocyrtus lignorum:

Isotoma

Genus Isotoma (Hopkin key #220) has:

• long macrosetae on all body segments
• ocelli CDE in straight line
• mucro with three teeth
• bothriotricha absent

Isotoma anglicana - Common, widespread, records are confused with I. caerulea/viridis.
Isotoma caerulea - Widespread but under-reported, records are confused with I. anglicana.
Isotoma riparia - Apparently scarce, only at edge of rivers, probably under-reported.
Isotoma viridis - Common, widespread, records are confused with I. anglicana/caerulea.

Burkhardt, U., & Filser, J. (2005) Molecular evidence for a fourth species within the Isotoma viridis group (Insecta, Collembola). Zoologica scripta, 34(2), 177-185: "For identification of single species within the Isotoma viridis group, we present polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) as a fast and efficient DNA‐based molecular method. We used five PCR primers amplifying the cytochrome oxidase II (COII) region (760 bp) of the mitochondrial DNA. The sequences clearly separated four species (I. viridis, I. riparia, I. anglicana and I. caerulea) out of samples from Norway, Sweden, Germany and Switzerland. Examination of genetic variation and phylogenetic relationship did not support the separation of two colour pattern forms of I. viridis into distinct species."

The species Isotoma anglicana/caerulea/viridis are troublesome and have been hugely confused. Contrary to what has sometimes been claimed it is not possible to distinguish between Isotoma anglicana/caerulea/viridis by habitus (general appearance - especially colour), they can only be reliably separated by microscopic examination of the manubrial 'teeth' and chaetotaxy of the dens (see below):
- Isotoma anglicana and Isotoma caerulea have two pairs of manubrial teeth on each side of the thickened apical edge of the manubrium.
- Isotoma viridis has a single pair of manubrial teeth.


Isotoma anglicana:





Isotoma viridis
Colour is highly variable, from yellow to almost black (possibly becoming darker with age). Juvenile:







- Ocelli C-D-E aligned (= Isotoma)
- One pair of manubrial teeth



Isotoma caerulea
Small specimens are usually green, becoming more blue in large specimens. Two pairs of manubrial teeth:




The key feature which separates Isotoma anglicana/caerulea is the chaetotaxy (arrangement of bristles (setae)) on the furca (see https://www.collembola.org/publicat/isotoma.pdf). Arne Fjellberg identified two differences:

a) The macrosetae at dorsal (anterior) side of dens, near the base:  I. caerulea has two,  I. anglicana has three. In practice, the dens is a forest of setae from which it is difficult to pick out individual hairs:


b) The macrosetae at dorsal side of manubrium. These macrosetae are also present in juveniles – even the first instar - and are often more easily observed in them. In Isotoma anglicana, the forward bristle A is longer and thicker than the rear bristle, B; in I. caerulea this is reversed:
I. anglicana  = A > B
I. caerulea =  A < B

Juveniles:





Adult (Photo Marie Huskens):



Isotoma riparia has a distinctive stripe down the middle of the body similar to Isotomurus palustris (which has more distinct lateral bands and no dark pigment between the eyes) but without trichobothria. Juveniles are a yellow colour similar to Isotomurus plumosus. One manubrial tooth. Only occurs in very wet habitats and has a distinctive stripe down the middle of the body - much like Isotomurus palustris, but without trichobothria. Photo Jan van Duinen:

Tetrad Coverage - Square Bashing for Springtails

My plan for 2019 is fairly simple, to get more organized about tetrad coverage. The tetrad (a 2x2 kilometre square based on the National Grid) is the standard unit for biological recording. One of my problems at the moment is that I don't have any software which is well suited to tetrad recording. However, using the NatureSpot Explore All Records tool which I'm currently basing the Atlas on, I can generate approximate tetrad records (with quite a bit of faffing about).

VC55 All Collembola records:


While the pattern of recording generally follows that for other taxons in VC55, what this current map reveals is that there are plenty of gaps to be filled. So far, so simple - drive almost anywhere and record springtails! The next step is a little more complicated - comparing VC55 Collembola records with other taxons. I have decided to adopt two benchmarks for this. The first is a comparison of springtail and woodlice records. I chose to use woodlice because while they are not too far away from springtails, they are more familiar to most people and the common species generate more records than springtails. Thus woodlice represent the next step up the recording hierarchy:



I'm moderately encouraged by this. As expected there are rather more woodlice records in VC55 but this clearly represents an achievable target. The second stage of benchmarking involes correcting for recording effort. Peter Shaw makes a strong case for adopting Orchesella cincta as a benchmark for recording effort/bias:

"... the genus Orchesella is taxonomically uncomplicated and species may be determined by eye using colour patterns. Distribution data for Orchesella species in the UK should therefore be reliable. The commonest and most distinctive is Orchesella cincta (Linnaeus, 1758), with 230 UK records of this species dating back to 1834 (Templeton 1835). The UK distribution map shows a strong bias towards the London area, with very few records in Cornwall, Wales or northern Scotland. Since the rst author of the present review has collected this species with approximately equal ease in all parts of England, Wales and the Scottish lowlands, this distributional bias in fact surely refects recorder bias, though its apparent absence from high mountains may be accurate, as it is said to be replaced by Orchesella alticola. In summary, the main infuence visible on the biogeography of this common, large and distinctive species in the UK is recorder bias. For less common or distinctive species this bias can only be worse."
Shaw, P., et al (2013) Updating taxonomic biogeography in the light of new methods–examples from Collembola. Soil Organisms, 85(3), 161-170.

VC55 Orchesella cincta records:


To date there are 29 tetrads with Orchesella cincta records, indicating the distance left to travel. It's not clear to me what represents an "acceptable" level of coverage, but these indicators at least allow measurement of progress.