Oribatids - Lower

Carboniferous 360-300mya

Plants Vascular Micro-aggregation Early Soils
Animals - Early & Late Origin of Insects

Let's look at oribatid clades and how they may related with soil formation in these times. Oribatid mites are one of the three most common animals found in soil today - the others being springtails and nematodes.

This is the animal group which probably plays the most monumentally important role in the history of our earth. We take it for granted that leaves and stuff from trees and plants are broken down by the deep living and surviving oribatids which carry bacteria in their guts for humification. But this does not seem to become widespread for another 100my with the arrival of 'higher' oribatids.

Yellow arrows signal body shape changes in this period.

This continues the story of oribatid evolution

400-360 mya (Late Devon)
330-300mya (Late Carb)
300 -250 mya (Permian)
Higher (200-145 mya Jurassic)
Mites (145-66 mya (Cretaceous)

Habits

These eight-legged creatures don’t have heads just bodies, and adapt to the changing conditions by being able to roll up in a ball, complete with the chemical trehalose (which we first came across in tardigrades 500mya) which can resist all sorts of extreme conditions. Rolled up they can withstand drought and pressure for long periods. So while soils are predominantly damp, these creatures can also withstand dramatic changes. There are several groups of mites found throughout the world, including Arctic and Antarctic.

All are generalist feeders, but some have specialised into composters or predators. This is a massive group. These are an order of mites, known as the "chewing Acariformes", clade Sarcoptiforms. Oribatid mites primarily feed on decomposing organic matter, including leaf litter, wood, and other plant debris. They are more capable of chewing and breaking down larger pieces of detritus compared than springtails.

Some estimates of development time from egg to adult are from several months while others are over two years in temperate forest soils. Oribatid mites have six active instars: pre-larva, larva, three nymphal instars and the adult. Following the pre-larva, they feed on a wide variety of living and dead plant and fungal material, lichens and even carrion. A few are predatory, but none parasitic.

Many species of oribatid mites require specific habitats, producing a wide diversity within the order, as they evolve to the many different niches. Some species are especially suited to dry conditions, or on bare lichen covered rocks. However most Oribatids prefer the moist forest floor litter.

Many people (including chatGPT) consider Humification has been an integral part of soil formation throughout history. Yet it wasn't widespread in Carboniferous times. Nor was de-lignification. It was not until the rise of white rot fungi 300-250mya that dead wood was broken down thoroughly. Humification would have been present in isolated areas but not widespread. That came much later - a good 100 million years later. The oribatids are a major player in humification then, but not much in this Period.

Shape

The evolution of body size, form, and an astonishing trophic diversity demonstrates that the soil food web was as structured as current food webs already in the Devonian, facilitating the establishment of higher plants in the late Paleozoic. (Schaefer & Caruso 2019. But in this Period there were only 'lower' oribatids. Their body shape and size changed in this Period, from small and elongate to somewhat larger and more globular. If we follow the plot of this site - that soil evolution reflects changing relations between animal vegetable and mineral - these body changes will reflect the rest of the environment in which they live. 'Larger' indicates the pores for running round got larger. But what does 'globular' tell us. It is beyond my architectural skills - but somebody may know.

Traits

"Traits that reflect differences in soil structure are body size and body form, because both determine the spatial niche oribatid mites occupy in the soil-matrix. Further, body size is not only very consistent within, and often distinct among taxonomic groups of oribatid mites, but also strikingly consistent among fossil and extant taxa, suggesting strong functional constraints on morphology. The diversity of trophic strategies and thus food web complexity is reflected by the many trophic levels covered by oribatid mites, which seems consistent within (adult) species (Maraun et al 2011) although a formal phylogenetic analysis of traits and trophic strategies has never been conducted. (Schaefer 2019)

"Although this interval contains the best anatomically preserved plant tissues with oribatid mite borings in the fossil record, coeval (ie those living at the same time) oribatid mite body-fossils are absent."...conundrum..

Oribatids in Swamps - conundrum

“Virtually every type of plant tissue was used by mites, notably indurated tissues such as bark, fibrovascular bundles and especially wood, as well as softer seed megagametophytic and parenchymatic tissues within stems, roots and leaves…as well as coprolites…. Oribatid mites were important arthropod decomposers in Pennsylvanian coals swamps of Euramerica." Yet, there is a conundrum. "Although oribatid mites are essential to the decomposition of plant tissues in modern temperate forests by assisting conversion of primary productivity to soil organic matter, little is known of their paleoecologic history. Previously there has been scattered and anecdotal evidence documenting oribatid mite detritivory in Pennsylvanian plant tissues. This study evaluates the incidence of oribatid mite damage for seven major coal-ball deposits from the Illinois and Appalachian sedimentary basins, representing a 17 million year interval from the Euramerican tropics. Although this interval contains the best anatomically preserved plant tissues with oribatid mite borings in the fossil record, coeval (ie those living at the same time) oribatid mite body-fossils are absent. By contrast, the known body-fossil record of oribatid mites commences during the Middle Devonian, but does not reappear until the Early Jurassic, at which time mite taxa are modern in aspect". They go on "the known body-fossil record of oribatid mites commences during the Middle Devonian, but does not reappear until the Early Jurassic, at which time mite taxa are modern in aspect." . We shall revisit oribatids at that time, and find a whole new wave of oribatids - 'higher' ones, joining in with "Termites and holometabolous insects making prominent contributors to this second wave of wood-boring" (Labandeira et al 1997)

That study of the role of oribatids in coal swamps found: “Oribatid mites mediate four major aspects of the degradation of plant tissues. First, they increase the surface of plant tissues through fragmentation, digestion, and defecation. The resulting pellets are preferentially colonized by microbial decomposers, such as yeasts and bacteria, when compared to adjacent, undigested plant tissues. Second, the incorporation of decomposer fungi in faecal pellets allows for germination of some fungi within the faecal pellet substrate often at some distance from the site of initial ingestion if the pellets sift through soil vugs or are biologically transported The ecological significance of this role has been debated. Third, oribatid mites create a "humus form" in which faecal pellets within the soil become cohesive and form a pelletal matrix of larger subunits resistant to decomposition. This conglomeratic formation forms a distinctive stratal structure in many temperate soils and provides a biotope for further colonization by microarthropods. Last, oribatid mites and other microarthropods and macroarthropods are pivotal in the vertical translocation of organic matter downward into the soil column, partly as an effect of ecologic guild succession during the decomposition process. Vertical translocation within an ‘absorptively-saturated humus’ additionally enhances the effect of nutrient leaching by rainwater” (Labandeira et al 1997)

Possible Conclusion

This is another animal group that were around in Devonian times but went missing until the Jurassic period. Was it just the fossils. Perhaps the fossils of lower oribatids did not preserve - although the swamp conditions would be good for that - because their exoskeletons were just of chitin. It was not until the more heavily armoured higher oribatids emerged did the fossils re-appear. Did that have something to do with 'lignin'?

Did these lower oribatids decompose - cellulose etc, but not lignin? This would explain a percentahe of decompositon but not all leaving the lignin debris - much like peat today/

They were good at chewin & pooin, but not so good at breaking down lignin. It is only when they do - 100my later that they become the little brown jobs - with lignin in their cuticle?

Studies have shown that the presence of oribatid mites can increase litter mass loss, stimulate microbial respiration rates and decrease fungal biomass.

These lower oribatid mites have three enzymes, cellulase, trehalase and chitinase, which gives them the ability to digest cell walls of plants and algae, and the contents of fungal hyphae. But NOT lignin.

Sex

In soils, many invertebrates reproduce by parthenogenesis (no sex please), but is most pronounced in oribatids and include many sexual and parthenogenetic (thelytokous) species.

Parthenogenetic appearance

Oribatid mite communities from different ecosystems and habitats across biomes, including tropical rainforests, temperate forests, grasslands, arable fields, salt marshes, bogs, caves, and deadwood were analysed. The percentage of parthenogenetic individual and species related to total oribatid mite density, species number, and other potential driving factors of the reproductive mode were interpreted in terms of two theories - the ‘Red Queen’ (sex in antagonistic conditions) hypothesis or the ‘Structured Resource Theory of Sex’(sex preferred when resources in short supply). The data showed that low density of oribatid mites due to harsh environmental conditions is associated with high frequency of parthenogenesis supporting predictions of the Structured Resource Theory of Sex rather than the Red Queen hypothesis (Maraun et all 2019).

"Oribatid mite species coloniz ing lichens, mosses, fungi (which often colonize substrates such as dead wood), and other living resources are predominantly sexual. Sexual species/taxa such as Phauloppia spp., Jugatala spp., Mycobates spp., Carabodes labyrinthicus, C. willmanni, Cymberemaeus cymba, and Micreremus brevipes dominated in lichens (as indicated by stable iso topes or observational studies). Oribatid mites in sporocarps of fungi also are mainly sexual species from the genera Carabodes, Siculobata, Caleremaeus, Autogneta and from the family Neoliodidae. Similarly, oribatid mites associated with mosses include mainly sexual species of the genera Minunthozetes, Melanozetes, Edwardzetes, Maudheimia, and Ameronothrus". (Maraun et all 2019). These are a mixture of lower and higher oribatids.

Carabodes

E.O. Wilson

E. O. Wilson says we desperately need experts to work on oribatids

He was a famous evolutionary biologist, who identified oribatids as among the "groups of organisms that desperately need experts to work on them”. He said that these characters are the most important animal group on – or rather – in earth and that we should have a Convention on Biodiversity, like the Climate Change one, and then these creatures should be more important than tigers and the like.

Distribution

Today, oribatids today dominate lower soil regions in many parts of the world - but not all. Their present day distribution helps tell us about their evolution (see Higher oribatids). They are more difficult to extract using standard Tullgren funnels than springtails. This is partly because they have further to come to escape the heat on the top and because they roll up to resist warmth or cold - and thus don't move in the funnels.

"The round to ovoidal body form was fixed in higher oribatid mites at the end of the Carboniferous." (Schaefer & Caruso 2019) They would be fitting into the pores already there, whereas later on - 100my later, they played a much greater role in actually structuring the soil.

A field study of oribatid mites (Maraun et al 2007) in soil found that species richness increased from high latitudes to more temperate regions, but did not increase further in the tropics.

They can move at 0.5-1cm per minute. Translated to human movement in terms of size/speed, it is not an Olympic runner, but bearing in mind the mud and boulders they go through without running shoes, a tenth of that speed was doing well.

Chewin’ n pooin’

Oribatids chew and chew. They chew chunks of plant debris – left behind by worms and they can chew small bits to make loads of poo. And that poo can coat the particles to make more aggregates. So newer building blocks are made that can make even more structures, and provide even more resilience and water holding.

If the worms are the engineers and the springtails the gardeners, oribatids are the builders and bricklayers. Millions of these mites throughout soils all over the world are responsible for chewing up lots of plant debris. They are the ones to prepare the chitin, and cellulose (and later, lignin) for the bacteria to have a go at. This becomes mite poo, photo right. Or should that be mighty poo, as it provides food for bacteria to get at, often setting up ‘hotspots’ of life in soils. Together with the springtail poo consisting of all sorts of complex - organic - chemicals, these two poos keep the world going round!

Oribatid poo

Hotspots

While all soils are heterogeneous, some bits are considered ‘Hotspots’. Microbial hotspots are microsites in soil with higher microbial activity and respiration rate compared to bulk soil and most frequently can occur round roots and aggregates. Yet, quite why they arrive where they do, and the significance of modern farming is still a subject to study. (Yadav et al 2019) put some money of oribatids being in there.

Poo study

That fascinating study, looking at mite poo “also compared the chemistry of mite faeces to unprocessed corn litter and found that faeces had a higher relative abundance of polysaccharides and phenols and a lower relative abundance of lignin. Our study establishes that S. moestus substantially changes litter chemistry during decomposition, but specific effects vary with initial litter quality. These chemical transformations, coupled with other observed changes in decomposition rates and nutrient cycling, indicate that S. moestus could play a key role in soil C cycling dynamics.” Feacal material taken during the course of the experiment showed that boluses contained both plant and microbial material. It would seem the stomachs of these small creatures are the mixing pot for the litter decomposition, throwing the ingredients close together. This is probably predominantly aerobic. The key character is that the mites can also withstand harsher, darker conditions and their bacteria adapt to the newer anaerobic conditions.

Bacteria

Wolbachia is the most abundant intracellular symbiont among terrestrial Arthropoda. This bacterium together with other microorganisms, i.e., Cardinium, gained fame mainly as the causative agent of host sex-ratio distortion. Across the impressive diversity of oribatid mites (Acari: Oribatida), the microbes have been found in both parthenogenetic (Oppiella nova, Ceratozetes thienemanni, Hypochthonius rufulus) as well as sexually-reproducing (Gustavia microcephala, Achipteria coleoptrata, Microzetorchestes emeryi, Damaeus onustus) species. Wolbachia found in Oribatida represents supergroup E and is related to bacterial endosymbionts of springtails (Hexapoda: Collembola).

Oribatids & Gut bacteria 1

Like many other organisms, oribatid mites have evolved symbiotic relationships with microorganisms, including bacteria, within their guts. The co-evolution of oribatid mites and their gut bacteria is believed to be a result of mutualistic interactions that have developed over evolutionary time scales. Here's an outline of how this co-evolution might occur:

Initial Association: The association between oribatid mites and gut bacteria likely began with random encounters between mites and environmental bacteria. Some bacteria that entered the gut of oribatid mites may have found favorable conditions for growth and colonization.
Beneficial Interactions: Over time, certain bacteria within the gut of oribatid mites may have provided benefits to their hosts. These benefits could include aiding in digestion, synthesizing essential nutrients, or protecting against pathogens.
Selective Pressures: As oribatid mites and their gut bacteria interacted, there would have been selective pressures acting on both parties. Mites with beneficial gut bacteria may have had a survival advantage, leading to the proliferation of these bacteria within the mite population. Similarly, bacteria that provided greater benefits to their hosts would have been favored through natural selection.
Co-evolutionary Dynamics: The relationship between oribatid mites and their gut bacteria is likely characterized by reciprocal adaptations. As mites evolved physiological features to accommodate and support specific bacterial communities, the bacteria may have co-evolved traits that optimize their survival and function within the mite gut.
Specificity and Diversity: Over time, the association between oribatid mites and gut bacteria may have become more specific, with certain bacterial species or strains being tightly associated with particular mite species or lineages. Additionally, the gut microbiota of oribatid mites may be diverse, with different bacterial taxa occupying distinct ecological niches within the gut.
Stability and Maintenance: Once established, the co-evolved relationship between oribatid mites and their gut bacteria would likely be stable and maintained across generations through mechanisms such as vertical transmission (from parent to offspring) and environmental acquisition (from the surrounding habitat).

Overall, the co-evolution of oribatid mites and their gut bacteria represents a fascinating example of symbiosis and highlights the intricate ecological and evolutionary dynamics that shape microbial associations in diverse ecosystems. We shall pick up later..

Oribatids & Gut bacteria 2

Bacteria in the alimentary canals of two oribatid mites, Rhysotritia sp. (Oribatida; Mixonomata; Euphthiracaroidea; Euphthiracaridae; Rhysotritia - lower) and Pergalumna sp.(Galumnidae) - higher, were examined from three different habitats. The three habitats included the mites'natural habitat and two artificial laboratory habitats, one with food and one without food. Gut microorganisms were obtained by dissecting paraffin-embedded, surface sterilized mites. Each alimentary canal and its contents, removed during dissection, were inoculated into 10 microbiological culture media. Bacteria, isolated from the oribatid gut, included: Bacillus, Pseudomonas, coryneforms, actinomycetes, Mycobacterium, Alcaligenes, Flavobacterium, Acinetobacter, and Citrobacter. Microorganisms from moss-soil samples of the oribatids natural habitat and laboratory foods were obtained and identified for comparison.

The microorganisms in the oribatid gut significantly (P < 0.05) changed with the oribatid species and with the oribatids' habitats. Rhysotritia and Pergalumna taken directly from the natural habitat and dissected, contained significantly lower frequencies of Bacillus and Pseudomonas isolations than those found in the moss-soil samples. After laboratory maintenance with food, dramatic shifts in the frequency of Bacillus and Pseudomonas were noted from both mites. A variety of bacteria were obtained from both oribatid species which had been starved for a period of 13 days.

Evolution

"Following the hypothesis of Grandjean (1969) oribatid mites consist of (1) the basal and most ‘primitive’ Palaeosomata, (2) the species rich Enarthronota including, for example, the Brachychthonioidea and Hypochthonioidea, (3) the small group Parhyposomata, (4) the ‘Mixonomata’, which includes groups like the Lohmannioidea, Eulohmannioidea and the box mites (Phthiracaroidea and Euphthiracaroidea), (5) the ‘Desmonomata’, a species rich group, including, for example, Nothridae, Hermanniidae, Camisiidae, Trhypochthoniidae and Malaconothridae, and (6) the species-rich Circumdehiscentiae (=Brachypylina, ‘Higher Oribatida’). In Grandjean’s system, the Circumdehiscentiae includes five groups, (a) Opsiopheredermata, (b) Eupheredermata, (c) dorsodeficient Apheredermata, (d) pycnonotic Apheredermata, and (e) Poronota (Trave´ et al. 1996). A hypothetical oribatid mite phylogeny, as extracted and modified from the works of Grandjean (1953, 1963, 1969), Haumann (1991) and Weigmann (1996) is offered" Maraun 2004 here..

There Is an oribatid from Ordovician times, but their main radiation is probably at this time - and through parthenogenesis. Parthenogenesis saves energy on sex so can live in these environments none others can -also grow slowly.. But how do their genes change for these adaptations - radiation? Maraun 2004

"Considering the central role of oribatid mites in the soil food web and their presence in terrestrial soils for >380 my, functional traits in this taxon likely evolved along with the developing aboveground vegetation and soils and the increasing complexity of roots, soil structure, and organic matter... with the development of soil six more oribatid mite species of six genera turn up in the Lower Carboniferous site of County Antrim, NI (~336–326 mya) (quoted in Schaefer & Caruso 2019)

Higher

Poronota, inc Scheloribatida

Nothridae

Malaconothridae

Phthiracaroidea

Lower..

Lohmannioidea

Eulohmannioidea

Parhypochthonioids

Hypochthonioidea

Enathronota

Palaeosomata

From the bottom - the oldest - to the top

There is a decline n the number of hairs

As you may expect if they are running more through tunnels than inside moss.

They could exploit /explore this better than rest, as

right size

wet/dry protection

no predators

and
capable of surviving adverse conditions.

It would be over hundred million years before they developed into the 'armadillo' (higher) oribatids found today in many - but not all - parts of the world.

Defense mechaism evolution in oribatids predation has been an important factor throughout the evolution of oribatid mites, contributing to morphological diversity

Oribatid evolution through fossils

But lets follow possible evolution of oribatids and the soil. In this period (Carboniferous) we see the lower oribatids in early soils. As they become more integral to the soil - a 100 million years later - they change shape, loose hairs and increase cuticle, possibly indicating more time in small tunnels and surviving worse conditions.

Numbers on nodes show the distribution of nodes with taxa known from the fossil record that were used as priors in the molecular clock analysis

Lower oribatids 400-320
earliest 407–385 mya;

8 Palaeosomata, 385–374 mya;

6–7, Parhyposomata/Enarthronota 336–326 mya;

Not sure...
4 Camisiidae, 85–83 mya;
5 Trhypochthoniidae 122–99 mya;

details and references see Supplementary information)

Significant shifts in body size and body form (black and orange arrows on timeline) Circles on nodes in the phylogeny indicate significant shifts in body size (black), body form (orange) Body form is clearly shifting during carboniferous.

It seems that only lower oribatids around at this time. Higher oribatids had to wait a couple of hundred million years..

Lower Oribatids

Age

400 -360 mya

Depth

0 - 2cm

hairy running round

Parhypochthonioids often overlooked as looks like a juvenile oribatid

360-300 mya

2-6cm

Going into the surrounding media,
and becoming entombed

Higher Oribatids

Much later..

200
mya

5 - 10 cm

Thicker cuticle to withstand worse conditions

Browness may be due to humic-related substances

Poronata - disturbed soil early successors. They include Scheloribates, I've counted thousands and they are v common worldwide

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