Convergent evolution

In evolutionary biology, convergent evolution or convergence is the process (! no, not process, but pattern). whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. On a molecular level, this can happen due to random mutation unrelated to adaptive changes; see long branch attraction.

note: have similar adaptations which are attributed to causes other than descent from common ancestors. gnerally attributed to natural selection as they adapt to similar environment or; however, convergent evolution can be looked at as the pattern of evolution and agnostic with respect to the actual mechanism — though some define as the process similar to how Darwinian evolution can be divided into theory of descent with modification (pattern) and theory of natural selection (process)

note: Luria et al. 1981, define convergence as: " The evolution of strikingly similar form, physiology, or behavior in two lineages that are not closely related to genealogy."

some may define as the process....

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 flight/wings of insects, birds, pterosaurs, and bats. All four serve the same function and are similar in structure, but each evolved independently. Some aspects of the lens of eyes also evolved independently in various animals.

note: However, just as evolution in the sense of the theory of descent with modification (the pattern of evolution) can be agnostic with respect to the mechanism (the process of evolution), coevolution can refer to only the observed pattern without the causal element.

Furthermore, theoretically, an alternative explanation for the observed harmony is design by a Creator.

Convergent evolution is similar to, but distinguishable from, the phenomena of evolutionary relay and parallel evolution. Evolutionary relay refers to independent species acquiring 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.

Animal examples

Mammals

• The marsupial Thylacine and placental Canids.

• 

  Thylacine, a canine-like marsupial

• 

  Golden Jackal, a true canine

• 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.
• 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.

Birds

• 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 auks in the Northern Hemisphere and penguins in the Southern Hemisphere.
• Vultures come in two varieties as 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

• The Flightless Cormorant of the Galapagos Islands, unlike other cormorants, now has wings developed for swimming rather than flight, equal in proportion to penguins.

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.
• 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 thaose 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 prehistoric fish-like reptile Ophthalmosaurus and the aquatic mammal Dolphins and Tuna
• The brachiopods and bivalve molluscs, which both have very similar shells

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.
• Euphorbia and many Cactaceae species both occur in hot, dry environments (see picture below) and have similar modifications.

• 

  Euphorbia obesa

• 

  Astrophytum asterias

Biochemical/molecular examples

• 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.

References

ISBN links support NWE through referral fees

• 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

Topics in evolutionary ecology
Patterns of evolution: Convergent evolution • Evolutionary relay • Parallel evolution
Colour and shape: Aposematism • Mimicry • Crypsis
Interactions between species: Mutualism • Cooperation • Predation • Parasitism

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