Category: Arthropods: Insects
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Arthropods are the most diverse and abundant organisms on Earth, and comprise an estimated 90% of animal species living today. The defining features of arthropods include possession of a hard, chitinous exoskeleton (part of a tri-layered cuticle), body segmentation, paired jointed appendages, specialisation of body regions into functional units ('tagma') and growth through periodic moulting of exoskeletal plates, triggered by cycles of ecdysteroid hormone. These features, and body tagmosis in particular, have brought extreme adaptability and ecological success, allowing arthropods to diversify into all available marine, freshwater and terrestrial habitats. Four major groups of living arthropods are recognised, namely the Chelicerata (spiders, mites, scorpions, horse-shoe crabs), Myriapoda (primarily centipedes and millipedes), Crustacea (crabs, shrimps, lobsters etc.) and Hexapoda (insects and their allies). Precise inter-relationships of these groups are contentious, but strong evidence suggests that sea-spiders (pycnogonids) are basal to chelicerates, and the remaining three groups form a derived clade of 'mandibulate' arthropods, with hexapods emerging from within the crustaceans.
Origins
True arthropods first appear as a diverse assemblage of marine animals in the Lower Cambrian (around 520 Ma ago). They included the lace-crab Marrella, various 'arachnomorph' taxa (e.g. the famous trilobites and horseshoe crab-like Aglaspis) and crustaceans. In the Silurian (443-417Ma), terrestrial arachnids, myriapods and crustaceans appear, while hexapods first appeared in the fossil record in the Early Devonian (around 400Ma, Rhynie Chert) with the collembolan Rhyniella praecursor and bristle-tail Leverhulmia mariae.
Classification
Hexapods occupy terrestrial and freshwater habitats, and are classified as either Entognatha or Insecta (Ectognatha). Entognathans include collembolans ('spring-tails'), proturans and diplurans, all of which are have mouthparts within the head, musculature throughout the antennal segments and ametabolous development (no visible change from nymph to adult stage). Insects (Ectognatha) are the most successful and prolific arthropods, with the beetles alone accounting for an astonishing proportion of global species diversity. They include the primitive wingless (apterygote) groups Archaeognatha (bristle-tails) and Thysanura/Zygentoma (silverfish), and winged (pterygote) insects. So-called palaeopteran pterygotes with four fixed wings include mayflies (Ephemoptera) and dragonflies (Odonata), whereas the majority of insects (neopterans) have hinges so that wings can fold down. Neopterans may be hemimetabolous, with gradual change from nymph to adult form (e.g. bugs, crickets, locusts, cockroaches, mantids), or holometabolous, showing complete metamorphosis (distinct larval, pupal and adult stages), as in beetles, butterflies, moths, wasps, ants, bees and flies for example.
Convergence
Insects provide innumerable and compelling examples of evolutionary convergence, many of which may well point to more general biological principles. One of many key examples is eusociality, which has evolved independently in insects several times, most famously in the ants (e.g. army and attine ants), bees, termites and aphids. Eusociality is associated with specialised modes of communication (e.g. pheromones, seismic vibrations) and unusual cognitive abilities in terms of learning and memory (e.g. in bees and wasps) and even teaching in certain ants (a remarkable trait only so far proven to be shared with humans, meerkats and pied babblers). A few tropical ant species (e.g. Cephalotes atratus) are capable of controlled gliding between trees, using aerodynamic lateral flaps and stereotyped postures in a similar way as do gliding frogs and lizards. Cultivation of nutritional fungi occurs in a number of insect groups (e.g. leaf-cutter ants, ambrosia beetles, termites, scale insects and gall midges). Agriculture in the form of fungal, algal or plant cultivation is also widespread in other animals, from dugongs and humans to damselfish and limpets.
Butterflies, praying mantids, stick insects and many other insects are masters of mimicry and camouflage, and the same form of deception is often arrived at in distantly related insects (e.g. leaf or twig-like stick insects, moths and crickets) and even in other arthropods (e.g. ant or beetle-like spiders). Another notable example of convergence is between nectar-feeding hummingbirds and 'hummingbirdoid' moths, which have evolved a stunningly similar body shape and flight pattern as an adaptation to the same ecological niche.
A few insects have acquire the ability to detect infrared radiation, a perception shared with certain snakes and vampire bats that look for IR to reveal the body heat of their warm-blooded prey. IR detecting insects include several beetles (e.g. Melanophila acuminata) that fly towards forest fires to lay eggs in burnt wood, and bed-bugs, that are guided by IR waves towards their human prey. Other insects produce light signals in the form of bioluminescence, a deeply convergent feature. To name but a few examples, 'fire flies' (which are actually beetles) flash to attract mates, fungus gnats use luminescent lines to lure prey and outside the insects many marine crustaceans (e.g. ostracods) and jellyfish (e.g. Perifila) use bioluminescence to confuse predators, deep sea squid can have flashing bodies and tentacles, and certain fish have bioluminescent eyes that serve as lamps in the darkness.
| Topic title | Teaser text | Availability |
|---|---|---|
| Vibrational communication in insects and spiders | Some spiders have evolved a most remarkable method of capturing other spiders – they imitate the vibrations of insects caught in their victim’s web. And this is only one of numerous intriguing examples of vibrational communication in arthropods… | Available |
| Migration in birds and insects | n/a | Unavailable |
| Co-operative breeding | n/a | Unavailable |
| Stridulation in insects and other animals | n/a | Unavailable |
| Pheromone use in animals, fungi and plants | n/a | Unavailable |
| Bioluminescence in arthropods | n/a | Unavailable |
| Ant-mediated seed dispersal (myrmecochry) | n/a | Unavailable |
| Teaching in humans, meerkats, birds and ants | n/a | Unavailable |
| Ant-eating (myrmecophagy) | n/a | Unavailable |
| Horned dung beetles (Onthophagus) and scarabs | n/a | Unavailable |
| Ultraviolet (UV) vision in insects and vertebrates | n/a | Unavailable |
| Agriculture in wood wasps | The most famous hymenopteran farmers are, without doubt, the attine ants. Rightly so, but they are not the only ones... | Available |
| Agriculture in gall midges (Diptera) | Flies, fungi, farming - sounds interesting? Read on if you want to learn about some rather different gall midges... | Available |
| Agriculture in beetles | Think of weevils and most likely you'll think of spoiled food. But some weevils have turned to farming... | Available |
| Vibrational communication in animals | What on earth could an elephant or treehoppers have in common with a seismometer? | Available |
| Malodorous flowering plants | Several groups of angiosperms have flower structures that produce foul odours to attract pollinating insects. This strategy is convergent, being found in species as distantly related as the 'Titan arum' Amorphophallus titanium (a monocot) and the 'Corpse flower' Rafflesia (a eudicot). | Available |
| Foam nests in animals | Nests crop up everywhere, but one made out of foam? Might not sound like a great idea, but it is. And no surprise, it has evolved several times... | Available |
| Flight muscle (arthrin) | n/a | Unavailable |
| Autumn leaf colouration | Autumn colours are likely to be adaptive, as the 'default' is simply to remain green up to leaf fall, and both red and yellow leaf colouration have evolved independently on many occasions in gymnosperms and woody angiosperms. | Available |
| Thermal sensing in mammals and insects | Insects and mammals have a group of ion channels (known as TRPs or Transient Receptor Potential channels) that are very similar and assumed to have a single origin. | Unavailable |
| Fungus-Insect associations | It is clear than an ascomycete yeast in a planthopper has been acquired quite independently of the beetles which employ a true yeast. | Unavailable |
| Thanatosis (feigning death) in spiders and insects | Beetles that "play possum"? A rather interesting example of convergence… | Available |
| Nuptial gifts in insects and spiders | Male dance flies lure females with a dead insect. Not very romantic, you might think, but it certainly does the trick. Hence, such nuptial gifts have evolved in numerous other arthropods... | Available |
| Foam for defence in insects | In the insects the capacity to make foam is important in several groups for defence, including in grasshoppers, moths, ants and spittlebugs. | Unavailable |
| Latex in plants and fungi | Latex is important in terms of defence not only because it typically gums-up attackers, notably insects, but often contains toxins. | Unavailable |
| Gliding lizards, frogs and ants | Tree-dwelling (‘arboreal’) ants capable of controlled gliding do so when dislodged or threatened by predation. Gliding species include members of three disparate families: Myrmicinae, Pseudomyrmecinae and Formicinae. | Available |
| Gliding reptiles | In the reptiles, different forms of skin membrane (called ‘patagia’) and in some extinct species, primitive feathers, have evolved convergently as adaptations for gliding. | Available |
| Parthenogenesis in Australian lizards and insects | “Evidence on the origin and spread of the two best-studied cases of parthenogenesis from the Australian arid zone, the grasshopper Warramaba virgo and the gecko Heteronotia binoei, suggests that they evolved in parallel.” – Kearney et al. (2006) Molecular Ecology vol. 15, p.1743 | Available |
| Nocturnal colour vision in moths, geckos and aye-ayes | Nocturnal colour vision is clearly convergent, and found in groups as disparate as the hawkmoths (insects), geckos (reptiles) and aye-aye (mammals). | Unavailable |
| Gregarious butterfly larvae | A particularly interesting example of gregariousness is found in the larvae of some butterflies; not only is it convergent but has evolved more than twenty times. | Unavailable |
| Olfaction: insights into convergence | Although olfaction is very widespread, there is abundant evidence for repeated convergence of key features, strongly suggesting that there really is an optimal solution to detecting smells. | Available |
| Infrared detection in insects | Whilst infrared detection is probably best known in the snakes (where it has evolved twice), in point of fact in terms of convergence the insects provide by far the most striking example. | Available |
| Infrared detection in animals | Some snakes are famous for 'seeing' infrared, but did you know that their heat-sensing abilities are rivalled by some beetles that can detect forest fires over considerable distances? | Available |
| Taste in arthropods and mammals | The ability to taste is obviously an essential component in the life of any animal, both to assess the potential quality of food, its nutrient capacities and also to detect toxins or other dangers. | Available |
| Camouflage in arthropods | Some insects make a “back-pack” of dead ants that evidently deters the attention of jumping spiders, while even more remarkably a weevil living in Papua hosts a garden on its back, complete with moss, algae and other organisms. | Unavailable |
| Corneal nipple arrays in insect eyes | Anti-reflection coating? Not only on mobile phone displays, but also on insect eyes... | Available |
| Milk production in tsetse flies and cockroaches | In at least some cases the cycle of milk secretory activity in tsetse flies and coackroaches is strikingly similar to that found in the mammary glands of mammals. | Unavailable |
| Lipocalins for milk and pheromone transport | Lipocalins are proteins that bind to and transport small hydrophobic molecules such as lipids and steroids, and have been associated with biological processes such as milk production, pheromone transport and immune responses. | Available |
| Compound eyes in arthropods | It is clear that amongst the arthropods as a whole the compound eye has evolved at least twice, and possibly even more times. | Available |
| Compound eyes in sabellid annelids | Compound eyes have evolved convergently in the annelids, notably amongst the sabellids, where they evidently serve as an optical alarm system. | Available |
| Scanning eyes in molluscs and arthropods | Some sea snails have a linear retina. What a hopeless arrangement, to see the world through just a narrow slit! Not quite, because they have come up with a rather intriguing trick to extend their visual field - and it's a trick too good to use only once. | Available |
| Camera-like eyes in arthropods | Arthropods are famous for their compound eyes, but some groups have had a fair crack at evolving the optically superior camera eye… | Available |
| Adhesive pads: from geckos to spiders | In terms of adhesive pads we find they have a remarkably wide distribution evolving in at least four distinct groups, including members of the reptiles, amphibians, arthropods and mammals, with tentative parallels in sea urchins. | Available |
| Pollen harvesting adaptations in bees (and honey-wasps) | n/a | Unavailable |
| Silk production and use in arthropods | Remarkably, fossil silk is known, especially from amber of Cretaceous age. Material includes both silk with trapped insects, possibly from an orb-web, and strands with the characteristic viscid droplets that are the key in trapping prey. | Available |
| Biological uses of silk: from webs to ballooning | What material is so versatile that it can be used for capturing prey, building nests, communication and even cleaning? The answer: that most remarkable of biomaterials - silk. | Available |
| Viviparity in insects | n/a | Unavailable |
| Hygiene in insects | n/a | Unavailable |
| Tool use in wasps | n/a | Unavailable |
| Endosymbiosis in wasps | n/a | Unavailable |
| Endoparasitism in wasps | n/a | Unavailable |
| Evolution of insecticide resistance | There are several varieties of insecticide, and each one is designed to knock out some metabolic or physiological capability of the insect, targeting a specific system. | Unavailable |
| Terrestrialization by arthropods | n/a | Unavailable |
| Sap feeding and honey-dew production in insects | Interestingly, it has now been shown that the saliva of the aphids has an analogue to the anti-coagulant properties of blood suckers, subverting the wound repair mechanism of the plant. | Available |
| Eusociality in aphids | A soldier caste has evolved in aphids multiple times. They are typically clonal and equipped with powerful claws or stylets, and in one group even horns. | Unavailable |
| Halteres in flies, strepsipterans and beetles | Halteres are balancing organs found in flies (dipterans) where the hind-wings are modified as balancing structures, and are convergent with the arrangement in the strepsipteran insects. | Unavailable |
| Butterflies and moths: insights into convergence | Some moths feed on the secretions from the tear-ducts of mammals, and some moths in Madagascar have evolved this independently, but instead of mammals they frequent birds. | Unavailable |
| Recruitment of endosymbiotic bacteria in insects | Independently the sap-feeding aphids and psyllids have recruited γ-proteobacteria, respectively best known from Buchnera and Carsonella, in an intimate and obligate symbiotic relationship. | Unavailable |
| Raptorial appendages in mantids and other arthropods | The praying mantises exercise a peculiar fascination, not only because of their lunging predatory habits, but also because on occasion the process of copulation ends with a decapitated male being chewed to pieces by the female while the reproductive movements continue. | Unavailable |
| Eusociality and agriculture in termites | Distinct hexamerins affect key growth hormones and help to regulate which caste type (e.g. worker or soldier) each individual develops into. | Unavailable |
| Strepsipterans: convergent halteres and eyes | Strepsipteran females spend their whole life inside a wasp. The males are rather more exciting, particularly in terms of convergence… | Available |
| Sleep in animals | Suffering from insomnia? Fruit flies do as well... | Available |
| Eusociality in arthropods and mammals | Eusociality is most familiar in the insects, where it has evolved several times, notably in bees, wasps, ants and termites, as well as in thrips and aphids. | Unavailable |
| Learning and memory in bees and wasps | n/a | Unavailable |
| Cognition in bees and wasps | Bees provide surprising insights into not only their cognitive abilities, such as the crucial distinction between same and different, but related features such as learning and memory. | Unavailable |
| Agriculture: from ants to dugongs | Human farmers tending their fields are a familiar sight. But don't forget about those fungus-farming termites or the fish with a garden of algae… | Available |
| Eusociality and communication in bees and wasps | The feature of bee communication that has attracted the most attention is the famous bee “dance” that relays information concerning location of productive areas for gathering nectar, pollen or water. | Unavailable |
| Senses and cognition in flies (dipterans) | Flies show intriguing convergences in various sensory modalities, notably in the senses of taste and hearing. | Unavailable |
| Beetles: insights into convergence | The beetles are probably the most diverse animal group on earth, so it is not at all surprising that they provide many fascinating insights into convergence. | Available |
| Agriculture in ants: leaf-cutters (attines) and non-attines | In some species, special squads leave the nest early each day, ascend the tree-trunks and then spend hours cutting out pieces of leaf that are dropped to other units on the ground. | Available |
| Eusociality and organisation in (army) ants | Army ants are permanently nomadic, and act as highly co-ordinated units that can form long files or fan out across the forest floor in search of prey. | Unavailable |
| Slavery | n/a | Unavailable |
| Trap-jaws in ants | Remarkable trap-jaw structures have evolved independently in various ants. | Unavailable |
| Insecticide production: from plants to primates | Application of insecticides, such as against mosquitoes, has been documented in several primates and birds. | Unavailable |
| Hummingbirds and hummingbirdoid moths | Like other birds hummingbirds are warm-blooded, but so independently are the hawk-moths, which like a number of insects have evolved thermoregulation. | Available |
| Ants: insights into convergence | Trap-jaws, silk and agriculture – just a few examples of convergence in the arguably most successful group of insects, the ants… | Available |
| Asexuality in insects | Viviparity has emerged in a number of insects, including the thrips and cockroaches. In the latter case the female also produces a “milk” for the nymphs. | Unavailable |
| Pheromones in arthropods | Not surprisingly this is a rich area of insights into evolutionary convergence because if an animal, such as a spider, can independently evolve the pheromone then a sexual lure is turned into a metaphorical honey trap. | Unavailable |
| Fleas and lice: insect ectoparasites | Insects are amongst the most successful of ectoparasites, and are well known from fleas and lice, both of which show evidence for convergences. | Unavailable |
| Locomotion in insects: walking and flying | It is now realized that the locomotory action of the walking legs in an insect such as a cockroach is strikingly similar to that found in mammals whereby the posterior legs are primarily propulsive whereas the anterior set have a more complex function that includes braking. | Unavailable |
| Haemocyanin in arthropods and molluscs | The degree of similarity between the active sites in arthropod and molluscan haemocyanin has been called “remarkable” and “startling”, but actually suggests that wherever in the universe life employs copper for aerobic respiration it will call upon haemocyanin. | Available |
| Transparent tissues: eyes, bodies and reflective surfaces | Read on if you want to know about the numerous animal equivalents to the invisible man... | Available |
| Alcoholism in mammals and flies | Identification of alcohol tolerance (or lack thereof) in different animal groups is important because alcoholism in humans may have some genetic basis. | Unavailable |
| Polarized light detection in arthropods, fish and cephalopods | In bees detection of polarized light from different quadrants of the sky is an important component in their navigation. | Unavailable |
| Hearing and ears in animals | Hearing has evolved independently in a number of groups, notably in the insects and vertebrates. | Unavailable |
| Moulting in arthopods, annelids and other animals | Moulting has, however, evolved independently in other groups, including the annelids where some polychaetes shed their jaws. | Unavailable |
| Mimicry in insects and other arthropods | Defensive mimicry is usually Batesian, where an innocuous species adopts the colouration of a toxic species, but Mullerian mimicry is also known whereby one species, already toxic, converges on the colouration of a more common toxic species. | Unavailable |
| Blood-brain barrier of vertebrates, cephalopods and other invertebrates | A very important component of complex brains is an effective barrier between the blood vascular system and the brain, both to regulate electrolyte balance (e.g. potassium) and exclude potentially harmful substances. | Unavailable |
