Category: Feeding
[Skip to list of Topics for this Category →]
Feeding is, of course, crucial for all heterotrophic organisms, which cannot derive their energy from light (like plants) or inorganic compounds (like many bacteria) but need to consume other organisms for nourishment. Many factors relating to feeding are rampantly convergent, be it with respect to morphological structures such as teeth and tongues, the techniques that organisms use to obtain food or the way they digest their food. Convergences range from the well known, such as the occurrence of three different feeding types in New World and Old World vultures, to the curious, such as "milk" production in some viviparous and ovoviviparous insects, which shows interesting similarities to mammals.
Teeth are a rich source of insight into evolutionary convergence, having evolved (and subsequently been lost) a number of times. Reptiles are particularly instructive, as many groups have independently diverged from typical simple dentition to evolve specialist adaptations which all find evolutionary parallels outside as well as within the reptiles. These specialisations include "beaks" for acquiring and processing food, interlocking chisel-like teeth or cusps to slice tough food material and sharp, robust caniniform teeth for seizing large prey. Toxic venom associated with some form of specialised dentition (e.g. fangs) has arisen a number of times within the reptiles, as well as in some mammal-like reptiles and even true mammals. Durophagy, the capacity to crush hard prey with particularly powerful jaws, has arisen many times in vertebrates, four times in cartilaginous fish alone. Molluscs possess a radula instead of teeth, with various functional and feeding requirements leading to significant convergences (e.g. in snails that scrape rock faces).
Protrusible tongues that can grasp an insect within milliseconds are not only a characteristic feature of chameleons and many amphibians but also a good example of evolutionary convergence as they have evolved several times, based on different morphology and mechanisms. Another way of rapidly gripping prey involves raptorial appendages, which can be found in several groups of insects (most famously mantids, but also mantaspids, neuropterans, heteropterans and flies) as well as mantid shrimps.
Suction feeding is the norm in teleosts but has also emerged independently in sharks, amphibians, a number of reptiles and even some aquatic mammals (e.g. the walrus). Other aquatic animals employ a specific mode of filter feeding, whereby marine plankton is filtered from the water by the intake of a considerable volume of water that is then expelled through a slitted curtain. This is most familiar in the baleen whales, but closely analogous arrangements have appeared in flamingos and broad-billed prions (also aptly known as the whale-birds).
Many animals use food sources that are not very accessible. Woodpeckers are famous for hammering holes into trees to obtain food, but several other birds have evolved woodpecker-like feeding habits as well. There are even tentative analogues among the mammals, such as the remarkable aye-aye, a Madagascan lemur that hunts for insects in wood by tapping with an enormously elongate middle finger. Nectar feeders, such as hummingbirds, sunbirds and "hummingbirdoid" hawk moths, show strikingly convergent adaptations. These include general body shape, an elongated tube for reaching into floral nectaries and hovering in a precise spot and also extend to metabolic, physiological and energetic convergences. Some species of desert lizards and many mammals (e.g. anteaters, pangolins, armadillos and numbats) eat ants (myrmecophagy) and have evolved shared anatomical adaptations. As ants do not need to be chewed, teeth are absent or reduced, while an elongated, rapidly protruding tongue enables fast prey capture and ingestion.
Some animals construct tools to obtain food. Advanced tool use for extracting or capturing prey (especially when other food sources are scarce) is known not only in humans but also in other primates (e.g. spear use in female chimps), cetaceans (e.g. protective sponge use in female bottlenose dolphins foraging on the sea bottom) and some corvids (e.g. stick tools in crows and rooks, cactus spine use in woodpecker finches). Silk, which is widely used in arthropods, can be considered as a simple "accessory" or tool to assist in feeding. Several spiders modify their webs to form structures to actively trap prey with, and a few insects (e.g. fungus gnats and caddisflies) use silk lines. Notably, a collagen-like equivalent of silk is ejected from the 'slime papillae' of velvet worms, covering prey with toxic, binding material.
Remarkably, a number of animals grow their own food - they have evolved agriculture. Many insects, most famously attine ants, termites and ambrosia beetles, maintain fungal gardens, while some herbivorous animals such as damselfish, marine worms, snails and dugongs farm fields of algae or sea-grass.
When food is hard to digest or deficient in particular nutrients, bacterial or fungal symbionts are often employed. Plant material, which consists mainly of cellulose, is notoriously difficult to break down. While the leaf-cutter ants have circumvented this problem by feeding leaves to a fungus that they then eat, many animals have evolved fermentation areas in their gut, where plant material is subject to prolonged bacterial attack. Foregut fermentation can be found in ruminants (e.g. cows, deer), monkeys, sloths, reptiles and some birds (e.g. the hoatzin) and regarding molecular mechanisms, the enzyme lysozyme has been recruited several times to aid digestion. Sap-sucking insects, such as aphids and phyllids, have independently acquired bacterial endosymbionts to provide those essential amino acids that the sugar-rich plant sap is lacking. Other organisms have responded differently to nitrogen shortage, for example several groups of fungi have independently evolved zoophagy, trapping and feeding on nematodes and other small prey. A similar strategy has been adopted by the carnivorous plants, where the ability to trap and digest insects has emerged at least six times.
| Topic title | Teaser text | Availability |
|---|---|---|
| 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 |
| Snail eating: an asymmetric diet | Snails may not be everyone's first choice on the menu but several distinct colubrid snakes have evolved expert techniques for gorging on these nutritious gastropods. | Available |
| Echolocation in bats | How can bats navigate in total darkness amongst trees and branches, but still locate a tiny, fluttering insect with extraordinary acuity? All made possible through echolocation, an astonishing sensory mechanism… | Available |
| Foregut fermentation in mammals | Foregut fermentation is best known from the ruminants, such as cattle, deer and giraffes, that regurgitate and rechew their food to aid microbial digestion. However, they are not the only mammals to have evolved this digestive strategy... | Available |
| Foregut fermentation in birds | A foregut-fermenting bird was long considered a paradox. But what about the hoatzin, a curious South American bird known locally as the "stinking pheasant" thanks to its smell of fresh cow manure? | Available |
| Filter-feeding rotifer anatomy | n/a | Unavailable |
| Chemosensory food detection in lizards and snakes | n/a | Unavailable |
| Carnivorous plants | All plants are harmless? Well, not quite - at least not when you're an insect... | Available |
| Marsupials with aye-aye-like digits | n/a | Unavailable |
| Ant-eating (myrmecophagy) | n/a | Unavailable |
| Agriculture in marine polychaete annelids | Some polychaetes attach pieces of algae to their dwelling tube. Just for decoration? No, but for a much more substantial (and convergent) benefit... | Available |
| 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 dugongs | When you think of grazing mammals, you might envisage large herds of antelopes roaming African savannahs. Did you know that there is an equivalent in the ocean, feeding on seagrass? | 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 |
| Agriculture in aquatic snails | Termites and ants are famous for tending fungal gardens, but did you know that also a marine snail farms a fungus? And this is not the only example of agriculture in this group… | Available |
| Agriculture in damselfish | Don’t be tempted to think human agriculture is unique. On many coral rocks, there are very similar things going on… | Available |
| Cichlids | Cichlids are one of the cause celebr� of evolution, and rightly so because these freshwater fish show a remarkable diversity and exemplify many key aspects of adaptive radiation. But why so successful? The answer lies in the versatility of the jaws (and yes, they are convergent). | Available |
| Pressure sensitivity and the tactile sense (excluding the lateral line) | The star-nosed mole is famous for, well, its nose, but do you have any idea what these peculiar 'tentacles' are for? The answer is rather touching and, of course, convergent... | Available |
| 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 |
| "Broken jaw" - mandibular and maxillary jaw joints | At first sight having a jaw with a joint seems a contradiction in terms, but such exist and not only are obviously functional, but needless to say convergent. | Available |
| Moray eels | Eels masquerading as snakes sounds interesting, and that is before they go hunting with their friends the groupers... � | Available |
| Hummingbirds, sunbirds and honeyeaters | One of the most well known examples of convergence among birds is between hummingbirds, sunbirds and honeyeaters, all of which are small, dominantly nectar-feeding birds. | Available |
| Suction feeding in fish, amphibians, reptiles and aquatic mammals | Probably everyone is familiar with the walrus, but did you know that it generates a vacuum in its mouth to suck clams out of their shells? And this is just one example of suction feeding, the feeding mode typically used by bony fish… | Available |
| Crustacean-trapping teeth in mesosaurs and crabeater seals | The multi-lobed post-canines of Lobodon carcinophagus are a functional analogue to the long, thin cage-like teeth of Mesosaurus, as both cage and prevent the escape of small crustacean prey. | Available |
| Teeth in aquatic reptiles | Aquatic reptiles tend to display one of three dentition types, well adapted to either seize and slice large vertebrate prey, pierce and gouge slippery fish, or entrap small prey such as crustaceans. | Available |
| Dental batteries in ceratopsians, hadrosaurs and elephants | The dental batteries or 'pavements' of ceratopsians and hadrosaurs evolved independently, and yet the dentition of several more distantly related animals also converges on their highly adapted tooth form. | Available |
| Teiid lizard dentition: convergence with other reptiles, mammals and fish | Teiids are skink-like lizards whose members show a stunning diversity of tooth types, providing rich evidence of convergence within the teiids themselves, in distantly related reptile groups and even in certain mammals and fish. | Available |
| Complex tooth occlusion in notosuchid crocodiles and tritylodonts (proto-mammals) | Two unusual Early Cretaceous crocodiles provide a shining example of convergence, as their dentition parallels that observed in a group of advanced proto-mammals called tritylodonts. | Available |
| Reptile dentition: convergence on complex occlusion | Some reptiles have transverse chisel-like teeth for slicing, and others have teeth bearing projections ('cusps') that interlock and slice or grind tough food. In each case evolutionary parallels are clear both within and outside the reptiles. | Available |
| Beak structures in reptiles and birds | Among reptile taxa with beak structures, we find several cases of convergent evolution, for example between turtles, Uromastyx lizards, a number of herbivorous dinosaurs and the tuatara (Sphenodon) of New Zealand. | Available |
| Venom and venom fangs in snakes, lizards and synapsids | Although the evolution of snake fangs itself provides us with a window on convergence, the presence of fang-like teeth in lizards, therapsids and mammals provides an even broader and more remarkable perspective. | Available |
| Feeding in snakes and lizards | The Turtle-headed sea snake feeds on small eggs and its feeding shows intriguing similarities to the way lizards forage, and herbivorous mammals graze and browse. | Available |
| Crabs: insights into convergence | You might think of crabs mainly as food, but this group is also highly instructive in terms of convergence… | Available |
| 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 |
| Carnivorous fungi: a diet of worms (and other animals) | Fungi have learnt how to trap living prey, notably nematodes but also a range of other animals include rotifers, tardigrades and even springtails. | Available |
| Ascomycete fungi: insights into convergence | Today ascomycetes are an extremely important group of fungi, and they take their name from the reproductive structures known as ascii. | Available |
| Bats: Insights into convergence | Bats show a fascinating array of convergences, from echolocation to flight to nectar feeding. Vampire bats can even detect infrared radiation, while others might be able to see into the ultraviolet end of the spectrum. | Available |
| Echolocation in toothed whales and ground-dwelling mammals | Given the extraordinary powers of echolocation in bats, it is not surprising that this group has received the most attention. However, they are not the only mammals to have evolved echolocation. Who invented sonar millions of years before the Navy? | 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 |
| Pharyngeal jaws in teleost fish | One of the great evolutionary breakthroughs in the teleost fish was the conversion of some of the elements that supported the gill bars into a second set of pharyngeal teeth that complemented the oral teeth. See how a fish becomes a snake! | Available |
| Durophagy (hard prey-eating) in fish | Plenty of animals have an extraordinary capacity to crush hard prey and this has evolved independently many times in the vertebrates. If you suspect it is a durophage, watch your fingers! | Available |
| Parasitic dinoflagellates | The majority of dinoflagellates are free-living, but they have adopted parasitism independently a number of times. | Unavailable |
| Dinoflagellate "nematocysts" | Examples of convergence within the dinoflagellates range from the evolution of a camera-like eye to stinging 'nematocysts' reminiscent of those in jellyfish. | Available |
| Ecological adaptations in Moloch and Phrynosoma lizards | Lizards of the genera Phrynosoma and Moloch have been considered a classic example of convergent evolution J. J. Meyers & A. Herrel (2005) The Journal of Experimental Biology, vol. 208, p. 114 | Available |
| Venom in mammals (and other synapsids) | Beware the venomous shrew! Yes, venomous. And convergent on some formidable lizards... | Available |
| Infrared detection in snakes | Warm-blooded rodents watch out! There are heat-sensing predators on the prowl... | 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 |
| Wire plants, moas and elephant birds | Madagascar and New Zealand were once home to giant herbivorous birds. And the plants have not forgotten... � � | 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 |
| Spitting in spiders and velvet worms | Scytodid spiders forcibly eject a mixture of saliva, silk and venom in a glutinous mass over a distance of c. 1cm to entrap 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 |
| Lysozyme | Lysozymes are common antibacterial enzymes that protect our eyes and nose from infection, but some animals have recruited them for a rather different purpose... | Available |
| Co-operative hunting | n/a | Unavailable |
| Filter feeding in whales, birds and reptiles | Filter feeding is most familiar in the baleen whales , but closely analogous arrangements have appeared at least twice in the birds, first the flamingos and second the sub-antarctic broad-billed prions. | Unavailable |
| Birds: insights into convergence | Intriguing ecological and morphological parallels can be found among the Neoaves. Many of these forms were initially believed to be each other's closest relatives, but are now widely recognised as classic examples of convergence. Think how similar swifts and swallows are, but they are only distantly related. | Available |
| Gut fermentation in herbivorous animals | Ever tried eating a newspaper? Don't. Plant cell walls contain cellulose, which is notoriously difficult to digest. Considering that all vertebrates lack the enzymes to attack this polysaccharide, how do so many of them manage to survive on a plant diet? | Available |
| Tool use in birds | What animals can drop stones into a water-filled tube to bring floating food within reach or bend wire to form a hook? Obviously chimpanzees? No, New Caledonian crows have evolved sophisticated tool use too. | Available |
| Sabre-toothed cats and marsupials | Marsupials with giant fangs? Yes, not all of the extinct sabre-toothed cats were actually cats… | Available |
| 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 |
| 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 |
| 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 |
| 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 |
| Woodpeckers and woodpecker-like birds and mammals | You think woodpeckers are unique? Consider the ovenbirds. Or even the curious aye-aye. | Available |
| Ecology and cosmetics in vultures | Vultures are not only charistmatic birds in the popular imagination, but are strikingly convergent, especially regarding feeding types... | Available |
| Molluscan radulas and boring organs | Most likely the radula is primitive to the molluscs, but not surprisingly the various functional and feeding requirements have led to significant convergence. | Unavailable |
| Tongues of chameleons and amphibians | Convergence in tongue function represents repeated morphological exploration within different lineages made possible by loss of an ancestral functional constraint | Available |
