Insects

200-150 mya Jurassic

Palaeosols Plants Ectomycorrhiza Earthworms Oribatids - Higher

COLEOPTERA - Beetles

Scarabs

The scarab beetles (Scarabaeidae), which include dung beetles, and cockchafers are believed, based on molecular and fossil evidence, to have first appeared in the Jurassic period.. "The ingroup-based fossil calibration of the tree widely confirmed a Jurassic origin of the Scarabaeoidea crown group. " (Ahrens et al 2014). But the great radiation of this group (Seidel et al 2023) occurred during the next period, when we will pick up their plot.

Ground beetles

Their suborder Adephaga are documented since the end of the Permian, about 250 Mya. Ground beetles evolved in the latter Triassic, having separated from their closest relatives by 200 Mya. The family, mostly carnivorous, diversified throughout the Jurassic, to become one of the 10 most species-rich families. The Jurassic fauna consisted of carabids (ground beetles - eg Tiger beetle) trachypachids (false ground beetles), aquatic gyrinids and haliplids. Some carabids eat springtails by spitting at them and sucking up the mush.

Green Tiger Beetle Cicindela campestris

One quite closely related, ravenous,rove beetle is Stenus. (Bauer & Pfeiffer 1991) Adults rove round throughout the year, particularly active over a long season from February/March until late in the autumn. They are mainly nocturnal, hiding by day in damp soil under debris or among matted vegetation.

Rove beetles

Ants were not the only insects, with a penchant for oribatids. Rove beetles had emerged in the previous period. They consume root maggot eggs and larvae, mites, springtails, insect eggs, or small insects on foliage. Most of the 6000 species of Staphylinids are predators of insects and other invertebrates, living in forest leaf litter and similar decaying plant matter. They are also commonly found under stones, and around freshwater margins. They are the long fast running beetles with small wing cases.

Termite-chomping rove beetles did not emerge until 100 mya

Southern Sister Clade

“The mostly southern hemisphere taxa together formed a sister grade to a well-supported clade of the remaining taxa of Staphylinini. Members of the latter clade occur mainly in the northern hemisphere or the tropics. The breakup of Pangaea in the Late Jurassic may have generated this striking bipolar distribution pattern of north versus southern hemisphere taxa, and suggests that the origin of Staphylinini may have occurred in the Middle Jurassic or earlier." (Brunke et al 2015)

Ant-like Stone Beetles

One Staphylinid, ant-like stone beetles (Scydmaeninae) has been observed feeding on armoured (Oribatida) and tortoise (Uropodina) mites, which play such an important role in soil biology. “This beetle feeds mostly on oribatid Scheloribatidae (60% of prey) and Oppiidae (30%) and only occasionally on uropodineUrodinychidae (4.5%) and oribatid Mycobatidae (3.5%). The number of mites consumed per beetle per day was 1.4, and when Oppianitens (Oribatid) was the prey, the entire feeding process took 3 –5.5 h."(Jaloszynski & Olszanowski 2015)

Some are able to skim over water. They become active on warm days when they may be observed running on the surface, often close to the water and usually in numbers. They ‘shoot’ springtails with a sticky rod (Bauer & Pfeiffer 1991) The behaviour of the beetle Stenus comma hunting three species of springtails was investigated. In almost half the attacks on prey, the beetle used its protrusible labium to catch the springtail. However, attacks using the labium were less successful when the springtail was large or was covered in scales or setae, as the prey item was more likely to become detached from the sticky tip of the labium. Thus, the beetle was more likely to attack large springtails without using its labium. These old ant-like stone beetles were much bigger then than now.

Considering the extremely similar body form and greatly extended appendages to those of existing species, the extinct Cascomastigus were likely to be predacious beetles, occurring in loose layers of leaf litter, and on the soil surface. They have been found in Baltic amber, a product of trees.

HYMENOPTERA

include bees, wasps and ants - all holometabolic. Hymenoptera are the third most speciose animal group on Earth, far surpassing the number of known vertebrate species. Hymenoptera in the form of Symphyta (Xyelidae) first appeared in the fossil record in the Lower Triassic. Hymenoptera include sawflies (link) which we saw emerged before this period.

Ants

There was another load of creatures to make the most of the rich soil lying about.

If you want to understand and measure the diversity of ants, the first place to start is to sample the leaf litter. A whole book has been written about how to do this, actually. That’s where the action is, in terms of functional and taxonomic diversity. Pretty much wherever you go on the entire planet, the most common creature that you’ll find in the litter is Pheidole. They’re cosmopolitan, if not sophisticated, scavenging on almost anything. If the importance of a taxon is measured by its diversity, abundance and distribution, then Pheidole are the most important ants.

See how ants feed on oribatids

Ants were the first holometabolous insects to spend most of their lives in or on soil. Some wasps, all the ants, and later bees, were also the first seriously social creatures on earth. Ants were able to build social communities under the protection of the litter layer, and developed distinct castes to collect and bring back to the nest to feed the next generation.

Nests

Ants build complex nests reacting with simple, local stimuli, using the space generated by digging, and leaf- and grass-cutting. “Most ants build their nests underground by digging into the soil to create space in the shape of tunnels and chambers. Workers transport the excavated soil outside and dispose of it forming a mound of variable height above the underground nest structure, which may protect the colony against flooding and help to ventilate the nest, for example in leaf-cutting ants… A single ant worker appears not to be able to create a complex nest as it only displays rather simple behaviours. However, by means of a combination of different mechanisms, namely templates, stigmergy (the trace left in the environment by an individual action stimulates the performance of a succeeding action) and self-organization, workers are able to coordinate their activities and build a complex structure adapted to a colony's needs" (Romer et al 2020)

Some species will dig very deep, with some nests over 5 meters deep, while others in areas that get snow, only dig about 4" down and often only dig beneath rocks. Lifta rock and you may see an entire colony.

Origins

Since the turn of the century, we’ve put the origins of ants earlier. Aculeata (means ‘having stingers) is subclade of Hymenoptera containing ants (Formicoidea), bees, and stinging wasps and the oldest ones are known fossil from a Late Jurassic formation in Kazakhstan. One estimate of their common ancestor lived in the Jurassic 162 mya. (Peter et al 2017)

Molecular clock

And molecularly they have to be bit earlier: “Moreau, Pierce and colleagues used a "molecular clock" calibrated with 43 fossils distributed throughout the ant family tree to date key events in the evolution of ants, providing a well-supported estimate for the age of modern lineages. Their conclusion that modern-day ants arose 140 to 168 million years ago pushes back the origin of ants at least 40 million years earlier than had previously been believed based on estimates from the fossil record.

Eusociality

Eusociality is a rare but successful life-history strategy that is defined by the reproductive division of labour. Ants (Formicidae) comprise the largest eusocial insect lineage in terms of described species (512,000) and often are ecologically dominant members of their communities

How often?

There are various arguments about how and how many times eusociality evolved. All ants are eusocial, and the origin of eusociality is clearly quite old in this group. The most recent molecular divergence dating analysis estimates (remembering molecular tend to date earlier) an age of 115–135 Ma for crown group ants, and thus eusociality must have originated sometime before that. Some taxa previously considered to reflect early ant eusociality, are the bulldog and dinosaur ants of Australia, but this depends on which sort of family tree researchers use. It seems several subterranean lineages, with the ability to withstand difficult conditions, were the earliest sorts. But it could be that large eyed wasps in exposed environments provided a better groundplan for ants. Ants throughout their history have used eusociality as a platform on which many behavioural specializations have evolved.

In eusocial species, most females forgo their own reproduction to support that of a dominant female or queen. In many eusocial insects, worker reproduction is inhibited via dominance hierarchies or by pheromones produced by the queen and her brood. (Knapp et al 2022)

Female wasps lay an egg and take care of the larva, which feed on fungus, until it pupated. These two phases became separated and their associated duties assigned to different individuals, namely queens and workers, during the evolution of eusociality.

Evolution

So, what prompted the evolution of this marvel of behaviour - eusociality? That was a question that puzzled Darwin in ‘The Origin of Species’.

Nest Hypothesis

What factors could prompt the evolution of this - sterile - worker caste? Years ago, we thought that ants evolved from wasps that laid their egg on other insects, and whose larvae then hatched on the host or in its nest. But you would not call these wasps “eusocial” - i.e. having reproductive queens with a nonreproductive female worker caste.

“Edward O. Wilson and his colleagues have suggested the “nest” hypothesis (Bos & d'Etorre 2012) was the important factor.” A clue to the origin of eusociality in ants, for the group of predatory wasps and bees (Apoidea) is both build nests needing defence, to contain their eggs, and they provide for those nests by bringing prey back to feed the offspring, and that these were important prerequisites for the evolution of eusociality.

This is one of the great puzzles of evolutionary biology. What induced certain living creatures to abandon solitary existence in favour of living in collaborative societies, as seen in the case of ants and other social, colony-forming insects? A major characteristic of so-called eusocial species is the division of labour between queens that lay eggs and workers that take care of the brood and perform other tasks, like building nests.

“How could sterile individuals continue to evolve? A careful reading of ‘the Origin(of Species)’ suggests that Darwin was not primarily concerned by the evolution of worker sterility itself, which he considered a minor difficulty. Some modern commentaries on Darwin and insect workers seem to be cases of present interests interfering with the interpretation of the past. From a modern perspective, the evolution of a worker caste, and its corollary altruism, are evolutionary puzzles inasmuch as natural selection normally favours greater, not lesser, individual reproduction. (Ratnieks et al 2011)

Altruism

Many people involved with evolution have considered this conundrum: How was there natural selection for ‘altruism’ – ie individuals sacrificing themselves for the good of the collective/race?

“These puzzles were resolved by Hamilton's theory of inclusive fitness. We now have a good functional understanding of how natural selection can cause both the origin of workers and their elaboration into greater levels of sterility and multiple morphological castes. Mechanistic understanding of morphological castes is also increasing via research into alternative developmental pathways. When ‘the Origin’ was written, genetics did not exist and it would have been virtually impossible for Darwin to elaborate such ideas.

However, ‘the Origin’ probably addressed the main questions in the minds of Victorian readers in relation to insect workers. Darwin was prescient in having insights with close relationships to modern-day interests and the key principles involved, including kinship and benefits to the colony, even if these are not exact precursors to modern thinking." (Ratnieks et al 2011)

However, I have another answer. It is very anthropomorphic to use the word ‘altruism’ for what goes on in these colonies. I suggest that if we are going to be anthropomorphic, we call it ‘slave labour’, as it is easier to explain in terms of natural selection. Division of labour in itself is not altruistic. Very often that division leads to exploitation, rather than altruism. So the term ‘worker caste’ is quite appropriate, as economics always shows that workers are exploited, even more so with slave labour. Still in anthropomorphic mode, stealing that labour and preventing sex, makes the colony more ‘productive’. This is easier to explain, and fits with some system of control exerted by ‘the queen’ (Johnson et al 2013)

Foreigners

A keystone in the evolution of sociality is the ability of group members to discriminate against ‘foreigners’. In social insects, colony social structure, number of queens, is generally thought to influence abilities of resident workers to discriminate between nestmates and non-nestmates. But does the social origin of introduced individuals have an effect?

“Using egg-acceptance bioassays, we tested the influence of social origin of queen-laid eggs on their acceptance by foreign workers in the ant Formica selysi. We showed that workers from both single- and multiple-queen colonies discriminated against foreign eggs from single-queen colonies, whereas they surprisingly accepted foreign eggs from multiple-queen colonies. Chemical analyses then demonstrated that social origins of eggs and workers could be discriminated on the basis of their chemical profiles, a signal generally involved in nestmate discrimination. These findings provide the first evidence in social insects that social origins of eggs interfere with nestmate discrimination and are encoded by chemical signatures." (Meunier et al 2011)

Reproductivity

But what is it that determines that a queen should lay eggs and that workers shouldn't reproduce one single gene called insulin-like peptide 2 (ILP2), which is probably activated by better nutrition, stimulates the ovaries and triggers reproduction. It may seem almost inconceivable that just one single gene should make all the difference. Yet “researchers drew their conclusion from a comparison of 5,581 genes in seven ant species in four different subfamilies that differ from each other with regard to numerous characteristics. But in one thing are they all alike: there is always a greater expression of ILP2 in the brain of reproductive insects. Queens thus have higher levels than workers. A further finding indicates that this peptide is found only in the brain, where it is produced in a small cluster of just 12 to 15 cells.”

Reproductive Signalling

Environmental cues that affect ant reproduction happen through altering neuroendocrine signalling. Environmental conditions such as temperature and crowding cause alterations to these neuroendocrine signalling networks in insects, particularly biogenic amine, ecdysone and JH signalling. These changes can occur rapidly (within 15 min of an acute environmental cue) and these rapid responses are collectively known as the neuroendocrine stress response (or ‘generic stress response’)These similarities in the response to different environmental cues and between diverse species indicate that there are some evolutionarily conserved aspects to neuroendocrine stress response.

Various chemicals may be involved. Nutrition may affect insulin signalling which seems to control clonal raider ants and their reproductive division of labour. Biogenic amines mediate aggressive behaviour in various insects and are important in generating dominance hierarchies in eusocial species. The ubiquitous biogenic amines octopamine (OA), serotonin (5-HT) and dopamine (DA) activate neural circuitry to regulate behaviour. Octopamine is often considered the major "fight-or-flight" neurohormone of invertebrates, and serotonin and dopamine are important to us human’s mood. In some ants, dopamine levels were associated with dominance status. The family tree of these ‘neuromodulators’ suggests a deep evolutionary history predating the origin of the nervous system. (Kamhi et al 2017)

Wasps

Apocrita, wasps in the broad sense, appeared in the Jurassic, and then diversified later. Fossils from Permian beds of Russia demonstrate that the wasp lineage is not as ancient as held before, and is related to alderflies and snakeflies. New fossils, which are 260-270 million years old, support his view, firmly attaching the wasp lineage to the lacewing (neuropteroid) branch of the holometabolan family tree and dating its origin no earlier than Late Permian. The wasp and snakefly ancestors were very small, indicating that these lineages have passed through a "miniaturization bottleneck.

Digger Wasps

A female Digger wasp prepares a nest, adding prey as food for her offspring, laying her eggs and then sealing up the nest. Shel digs a burrow, using spiny brushes on her legs, up to 30cm deep. The tunnel usually branches at the end and each branch will have a separate egg laid in it. Her energy is repaid as an advantage to her offspring. The surface of bare ground has a desert-like microclimatic condition, so gets very hot in the sun and at night the surface can cool very fast. A deep tunnel protects the eggs against these extremes. That is what the soil does.

Fungus Gnats

Another group of insects which flew in to make the most of the dead wood lying about were the fungus gnats. These flies (Diptera) occur around damp, decaying vegetation, algae, and fungi. Their larvae make the most of the dead matter and would feed on the fungi associated with forests, which then consisted mainly of conifers

The gnats emerged in the Late Jurassic and have diversified enormously all over the world. The main family (Mycetophilidae - Greek for “fungus lovers”) has more than 600 described speciesTheir larvae feed on mushrooms, puffballs, moulds, and other wood-decay (xylophagous) fungi.

Two researchers spent 15 years tracking down fungus gnat family history with the aid of little more than a microscope, a featherweight forceps, and well-trained eyes and they produced a comprehensive study on fungus gnats. One of those researchers says that the insect found in the amber in 1993 film Jurassic Park, was not a mosquito as the plot would have us believe, but is actually a fungus gnat - belonging to the family Keroplatidae.[2]This is beyond me to referee, as there were mosquitoes about and so too were the fungus gnats swarming at dinosaurs’ feet. But they would not have bitten any dinosaurs to provide blood for the film.

Fungus gnat larvae

Insects were running round the surface of the ground, many now feeding on mites and springtails. They would take off dramatically in the next, Cretaceous,period

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