Category: Defence
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Defending yourself is absolutely crucial when you are an animal preyed upon by a predator or a plant that is attacked by herbivores, and it is of no minor importance to be able to resist infection by pathogens or parasites. Due to the ubiquitous nature of these problems but limited possibilities for solving them, it is no wonder that very different groups of organisms have arrived at very similar solutions.
When it comes to defence against being eaten, one mechanism employed is to make yourself invisible to predators. Such camouflage is often visual, and the octopus for example is a master of melting into its environment. Visual camouflage can be found in numerous other groups of animals (and even in plants!) and sometimes even involves decorating yourself with objects from your surroundings. Decoration has evolved independently in, for example, spider crabs and a species of weevil that both host a garden of algae and other organisms on their back. Astonishingly, camouflage can also be olfactory - several species of mammal (e.g. ground squirrels, Siberian chipmunks, hedgehogs and tenrecs) anoint themselves with the scent of poisonous animals, such as snakes or toads.
To avoid ending up as a meal many organisms are toxic, and this approach is rampantly convergent, too. The sequestration of chemicals such as alkaloids for defensive purposes has evolved numerous times, such as in frogs, many insects, myriapods, some birds (e.g. the New Guinean pitohuis), tunicates and, of course, plants. Toxicity is often correlated with bright warning colours (referred to as aposematic colouration) that signal to potential predators. In frogs alone, this correlation between toxicity and colouration has evolved several times. Harmless organisms regularly exploit the aposematic colours of toxic or unpalatable species by mimicking them. This type of mimicry is known as Batesian mimicry, whereas in Muellerian mimicry aposematic organisms mimic each other.
Alternative means of defence are protective structures, such as spines. Defensive spines can be found in numerous animals (e.g. sea urchins, insects, some fish, lizards, hedgehogs, porcupines and other spiny mammals) and, of course, in many groups of plants. In some eusocial insects (eusociality representing a key example of convergence in itself), defence of the colony is undertaken by a specialised soldier caste, characterised by features such as large body size or massive mandibles.
Defensive secretions are widespread, including ink in cephalopods and sea-hares (Aplysia), foam in several groups of insects (most famously the spittlebugs but also in some grasshoppers and moths) and latex that is produced by many plants from different groups to gum-up attackers. Latex additionally illustrates that the evolution of counter-defences can be convergent, too - a number of insects have independently arrived at methods of sabotaging the plants' lactiferous system.
In defence against pathogens and parasites, elements of an immune system have evolved not only once but several times. The non-specific innate immune system can be found in many animals as well as in plants, but even the highly specialised adaptive immune system has not only been invented by the jawed fish. It has recently been discovered that jawless fish have a similar system that relies on different mechanisms and components, and also the insect immune system shows at least some parallels.
| Topic title | Teaser text | Availability |
|---|---|---|
| Gliding in spiders, ants and other arthropods | n/a | Unavailable |
| Bioluminescence | Flying through the air on a summer's evening or sparkling in the ocean you may see magical flashes of light that signal some of nature's most enchanting creatures, those that are bioluminescent. | Available |
| Defensive enrolment | Curling up into a ball has evolved many times as an excellent anti-predator defence. | Unavailable |
| Brood parasitism in cuckoos and other birds | Obligate brood parasitism has evolved several times independently in birds. Apart from the cuckoos, it can be found in four other, only distantly related families. | 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 |
| Peroxidases and oxidases | n/a | Unavailable |
| Pufferfish (and inflation) | Pufferfish are some of the most extraordinary fish to have evolved, especially because of their capacity to swallow water and inflate themselves to something like a football. Not only that but some representatives can be deadly to the unwary diner... | Available |
| Anointing in mammals | The strategy of anointing the body with the scent of a more dangerous animal has evolved independently several times, including in rodents, hegdehogs and tenrecs. | Available |
| 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 |
| Tetrodotoxin | Not many foods served in a restaurant can kill you, but pufferfish is the exception. Tetrodotoxin, the toxin responsible for such culinary fatalities, reveals a fascinating story of convergent evolution... | Available |
| Desert plants with succulent leaves | Perhaps the most striking case of convergence among leaf succulents occurs between Agave and its relatives Yucca and Hesperaloe in the Americas and Aloe and its relatives (e.g. Haworthia and Gasteria) in Africa. | Available |
| Thanatosis (feigning death) in spiders and insects | Beetles that "play possum"? A rather interesting example of convergence… | Available |
| Ink production in cephalopods and gastropods | A series of striking convergences can be found in the sea-hares (Aplysia), a group of gastropods and only remotely related to the cephalopods.� Not only do they emit ink clouds (the colour is derived from ingested red algae), but they also employ chemical cues that assist in defense. | 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 |
| 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 |
| Venom in mammals (and other synapsids) | Beware the venomous shrew! Yes, venomous. And convergent on some formidable lizards... | 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 |
| Defensive spines in animals | Sea-urchins, porcupines (and porcupine fish), lizards and many other animals bristle with defensive spines. | Unavailable |
| Corneal nipple arrays in insect eyes | Anti-reflection coating? Not only on mobile phone displays, but also on insect eyes... | Available |
| Wire plants, moas and elephant birds | Madagascar and New Zealand were once home to giant herbivorous birds. And the plants have not forgotten... � � | Available |
| Innate and adaptive immune systems | A vile cough, soaring temperature? When attacked by nasty microbes, our immune system comes in handy. Surprisingly (or not), plants have come up with a very similar solution to dealing with pathogens, but independently... � � | 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 |
| Alkaloids and other chemical defences | n/a | Unavailable |
| 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 |
| 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 |
| Myriapods (centipedes and millipedes): defence and terrestrialisation | This group of arthropods is also important because they show independent invasion of the land (terrestrialization), which not surprisingly has led to important convergences. | Unavailable |
| 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 |
| Gastropod molluscs: snail shell anatomy | Snail shells typically form a helical spiral, but within this geometry there is a considerable degree of convergence. | Unavailable |
| Transparent tissues: eyes, bodies and reflective surfaces | Read on if you want to know about the numerous animal equivalents to the invisible man... | Available |
| Defence in frogs: toxins and camouflage | The many striking examples of convergence most famously include the case of mimicry, but the question of defence also extends to the use of toxins (and venoms), such as alkaloids, where we also find molecular convergence. | Available |
| 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 |
| Camouflage and mimicry in cephalopods | The most familiar examples of colour change in cephalopods are related to camouflage, but there are also striking examples of sexual and defensive (Batesian) mimicry. | Unavailable |
| Reflective tissues | Other cephalopods achieve reflectivity by employing collagen fibrils, of which the deep-sea Vampyroteuthis is perhaps the most striking example. | Unavailable |
