Convergent evolution

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In evolutionary biology, convergent evolution is the process whereby organisms that are not monophyletic (not closely related) independently evolve similar traits as a result of having to adapt to ecological niches or similar environments.^[1] The opposite of convergent evolution is divergent evolution, whereby related species evolve different traits. On a molecular level, this can happen due to random mutation unrelated to adaptive changes; see long branch attraction.

In cultural evolution, convergent evolution is the development of similar cultural adaptations to similar environmental conditions by different peoples with different ancestral cultures.

An example of convergent evolution is the similar nature of the wings of insects, birds, pterosaurs, and bats. All four serve the same function and are similar in structure, but each evolved independently and not from a common winged ancestor. The striking similarities between hummingbird moths and hummingbirds is another example of convergent evolution.

Convergent evolution is similar to, but distinguishable from, the phenomena of evolutionary relay and parallel evolution. Evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems, but not at the same time (e.g. dorsal fins of extinct ichthyosaurs and sharks). Parallel evolution occurs when two independent species evolve together at the same time in the same ecospace and acquire similar characteristics (extinct browsing-horses and extinct paleotheres).

Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures, which have a common origin. Bat and bird wings are an example of analogous structures, while the bat wing is homologous to human and other mammal forearms, sharing a common ancestor despite serving different functions by modern species.

[edit] Animal examples

The skulls of the Thylacine (left) and the Timber Wolf, Canis lupus, are almost identical although the species are unrelated. Studies show the skull shape of the Red Fox, Vulpes vulpes, is even closer to that of the Thylacine.^[2]

Mammals

• The marsupial Thylacine and placental Canids.
• Several mammal groups have independently evolved prickly protrusions of the skin, called spines - echidnas (monotremes), hedgehogs (insectivores), Old World porcupines (rodents) and New World porcupines (a separate group of rodents). In this case, because the two groups of porcupines are relatively closely related, they would be considered to be an example of parallel evolution; neither echidnas nor hedgehogs, however, are closely related to rodents at all. In fact, the last common ancestor of all four groups was a contemporary of the dinosaurs.
• Cat-like, sabre-toothed predators evolved in three distinct lineages of mammals — sabre-toothed cats, Nimravids (false sabre-tooths), and the marsupial thylacosmilids. Gorgonopsids and creodonts also developed long canines, but that is the only physical similarity.
• A number of mammals have developed claws and long, sticky tongues that allow them to open the homes of social insects (e.g. ants and termites) and eat them. These include the four species of anteater, about 20 species of armadillo, eight species of pangolin, the African aardvark, four species of echidna, and the Australian numbat.
• Koalas of Australasia have evolved fingerprints, very similar to those of humans.
• The Australian honey possum has developed a long tongue for taking nectar from flowers, the same sort of structure that butterflies possess to accomplish the same task.
• The North American kangaroo rat, Australian hopping mice and African / Asian jerboa have all developed convergent adaptations for their respective desert environment, including a small, rounded body shape with very large hind legs and long, thin tails, the characteristic hopping bipedal gait, and nocturnal, burrowing behaviour. The creatures occupy similar niches in their respective ecosystems.

Avian and Non-avian Dinosaurs

• Ornithischian (bird-hipped) dinosaurs had a pelvis shape similar to that of birds, but avian dinosaurs evolved from saurischian (lizard-hipped) dinosaurs.
• The Little Auk of the north Atlantic (Charadriiformes) and the diving petrels of the southern oceans (Procellariiformes) are remarkably similar in appearance and habits.
• The similar evolution of penguins in the Southern Hemisphere and flightless wing-propelled diving auks in the Northern Hemisphere - the Atlantic Great Auk and the Pacific mancallines.
• Vultures are a result of convergent evolution: both Old World vultures and New World vultures eat carrion, but Old World vultures are in the eagle and hawk family and use eyesight for food discovery; the New World vultures are related to storks and use the sense of smell (as well as sight) to find carrion. In both cases they search for food by soaring, circle over carrion, and group in trees, and both have featherless necks.

Nubian vulture, an Old World vulture

Turkey vulture, a New World vulture

Hummingbird, a New World bird, with Sunbird, an old world bird

• Hummingbirds and Sunbirds. The former live in South America and belong to a distinct order, while the latter live in Africa and are a family in the order Passeriformes.
• Certain longclaws (Macronyx) and meadowlarks (Sturnella) have essentially the same striking plumage pattern. The former inhabit Africa and the latter the Americas, and they belong to entirely different lineages of Passerida. While they are ecologically quite similar, no satisfying explanation exists for the convergent plumage; it is best explained by sheer chance.

Other

• The similarities in diet and activity patterns between the thorny devil (Moloch horridus) and the Texas horned lizard (Phrynosoma cornutum) both in different clades.
• Modern Crocodilians, and prehistoric phytosaurs, champsosaurs, and certain labyrinthodont amphibians. The resemblance between the crocodilians and phytosaurs in particular is quite striking.
• The Neotropical poison dart frog and the Mantella of Madagascar have independently developed similar mechanisms for obtaining alkaloids from a diet of ants and storing the toxic chemicals in skin glands. They have also independently evolved similar bright skin colors that warn predators of their toxicity–(by the opposite of crypsis, namely aposematism).
• Assassin spiders are a group comprising two lineages that evolved independently. They have very long necks and fangs proportionately larger than those of any other spider, and hunt other spiders by snagging them from a distance.
• The smelling organs of the terrestrial coconut crab are similar to those of insects.
• The body shape of the prehistoric fish-like reptile Ophthalmosaurus and other ichthyosaurians, dolphins (aquatic mammals), and tuna (scombrid fish).
• The brachiopods and bivalve molluscs, which both have very similar shells.
• The limpet-like form in several lines of gastropods: "true" limpets, pulmonate siphonariid limpets and several lineages of pulmonate freshwater limpets.
• Death Adders strongly resemble true vipers, but are in fact elapids.
• Large Tegu lizards of South America have converged in form and ecology with Monitor lizards, which are not present in the Americas
• Chiclids of South America and Sunfish of North America are strikingly similar in morphology, ecology and behavior. The Peacock Bass and Large Mouth Bass are excellent examples.
• The notochords in chordates and the stomochords in hemichordates.

[edit] Plant examples

• Prickles, thorns and spines are all modified plant tissues that have evolved to prevent or limit herbivory, these structures have evolved independently a number of times.
• The aerial rootlets found in ivy (Hedera) are similar to those of the climbing hydrangea (Hydrangea petiolaris) and some other vines. These rootlets are not derived from a common ancestor but have the same function of clinging to whatever support is available.
• Similar-looking rosette succulents have arisen separately among plants in the families Asphodelaceae (formerly Liliaceae) and Crassulaceae.
• The Euphorbia of deserts in Africa and southern Asia, and the Cactaceae of the New World deserts have similar modifications (see picture below for one of many possible examples).

Euphorbia obesa

Astrophytum asterias

[edit] Examples for convergent evolution of enzymes and biochemical pathways

• The existence of distinct families of carbonic anhydrase is believed to illustrate convergent evolution.
• The use of (Z)-7-dodecen-1-yl acetate as a sex pheromone by the Asian elephant (Elephas maximus) and by more than 100 species of Lepidoptera.
• The independent development of the catalytic triad in serine proteases independently with subtilisin in prokaryotes and the chymotrypsin clan in eukaryotes.
• The repeated independent evolution of nylonase in two different strains of Flavobacterium and one strain of Pseudomonas.
• The biosynthesis of plant hormones such as gibberellin and abscisic acid by different biochemical pathways in plants and fungi.^[3][4]
• ABAC is a database of convergently evolved protein interaction interfaces. Examples comprise fibronectin/long chain cytokines, NEF/SH2, cyclophilin/capsid proteins. Details are described here.

[edit] References

1. ^ Online Biology Glossary
2. ^ L Werdelin (1986). "Comparison of Skull Shape in Marsupial and Placental Carnivores". Australian Journal of Zoology 34 (2): 109–117. 
3. ^ Tudzynski B. (2005). "Gibberellin biosynthesis in fungi: genes, enzymes, evolution, and impact on biotechnology". Appl Microbiol Biotechnol. 66: 597-611. doi:10.1007/s00253-004-1805-1. PMID 15578178. 
4. ^ Siewers V, Smedsgaard J, Tudzynski P. (2004). "The P450 monooxygenase BcABA1 is essential for abscisic acid biosynthesis in Botrytis cinerea.". Appl Environ. Microbiol. 70: 3868-3876. doi:10.1128/AEM.70.7.3868-3876.2004. PMID 15240257. 

• Rasmussen, L.E.L., Lee, T.D., Roelofs, W.L., Zhang, A., Doyle Davies Jr, G. (1996). Insect pheromone in elephants. Nature. 379: 684
• Convergent Evolution Examples- Ecological Equivalents, Department of Biology, Bellarmine University
• Conway Morris, Simon (2003). Life's Solution: Inevitable Humans in a Lonely Universe. Cambridge University Press. ISBN 0-521-60325-0.