Convergent evolution

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Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution_sentence_0

Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. Convergent evolution_sentence_1

The cladistic term for the same phenomenon is homoplasy. Convergent evolution_sentence_2

The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight. Convergent evolution_sentence_3

Functionally similar features that have arisen through convergent evolution are analogous, whereas homologous structures or traits have a common origin but can have dissimilar functions. Convergent evolution_sentence_4

Bird, bat, and pterosaur wings are analogous structures, but their forelimbs are homologous, sharing an ancestral state despite serving different functions. Convergent evolution_sentence_5

The opposite of convergence is divergent evolution, where related species evolve different traits. Convergent evolution_sentence_6

Convergent evolution is similar to parallel evolution, which occurs when two independent species evolve in the same direction and thus independently acquire similar characteristics; for instance, gliding frogs have evolved in parallel from multiple types of tree frog. Convergent evolution_sentence_7

Many instances of convergent evolution are known in plants, including the repeated development of C4 photosynthesis, seed dispersal by fleshy fruits adapted to be eaten by animals, and carnivory. Convergent evolution_sentence_8

Recent evidence suggests that even plants and animals share a convergently evolved developmental pattern whereby embryos of both lineages pass through a phylotypic stage marked by an organizational checkpoint during mid-embryogenesis. Convergent evolution_sentence_9

Overview Convergent evolution_section_0

Further information: List of examples of convergent evolution Convergent evolution_sentence_10

In morphology, analogous traits arise when different species live in similar ways and/or a similar environment, and so face the same environmental factors. Convergent evolution_sentence_11

When occupying similar ecological niches (that is, a distinctive way of life) similar problems can lead to similar solutions. Convergent evolution_sentence_12

The British anatomist Richard Owen was the first to identify the fundamental difference between analogies and homologies. Convergent evolution_sentence_13

In biochemistry, physical and chemical constraints on mechanisms have caused some active site arrangements such as the catalytic triad to evolve independently in separate enzyme superfamilies. Convergent evolution_sentence_14

In his 1989 book Wonderful Life, Stephen Jay Gould argued that if one could "rewind the tape of life [and] the same conditions were encountered again, evolution could take a very different course". Convergent evolution_sentence_15

Simon Conway Morris disputes this conclusion, arguing that convergence is a dominant force in evolution, and given that the same environmental and physical constraints are at work, life will inevitably evolve toward an "optimum" body plan, and at some point, evolution is bound to stumble upon intelligence, a trait presently identified with at least primates, corvids, and cetaceans. Convergent evolution_sentence_16

Distinctions Convergent evolution_section_1

Cladistics Convergent evolution_section_2

Main article: Cladistics Convergent evolution_sentence_17

In cladistics, a homoplasy is a trait shared by two or more taxa for any reason other than that they share a common ancestry. Convergent evolution_sentence_18

Taxa which do share ancestry are part of the same clade; cladistics seeks to arrange them according to their degree of relatedness to describe their phylogeny. Convergent evolution_sentence_19

Homoplastic traits caused by convergence are therefore, from the point of view of cladistics, confounding factors which could lead to an incorrect analysis. Convergent evolution_sentence_20

Atavism Convergent evolution_section_3

Main article: Atavism Convergent evolution_sentence_21

In some cases, it is difficult to tell whether a trait has been lost and then re-evolved convergently, or whether a gene has simply been switched off and then re-enabled later. Convergent evolution_sentence_22

Such a re-emerged trait is called an atavism. Convergent evolution_sentence_23

From a mathematical standpoint, an unused gene (selectively neutral) has a steadily decreasing probability of retaining potential functionality over time. Convergent evolution_sentence_24

The time scale of this process varies greatly in different phylogenies; in mammals and birds, there is a reasonable probability of remaining in the genome in a potentially functional state for around 6 million years. Convergent evolution_sentence_25

Parallel vs. convergent evolution Convergent evolution_section_4

When two species are similar in a particular character, evolution is defined as parallel if the ancestors were also similar, and convergent if they were not. Convergent evolution_sentence_26

Some scientists have argued that there is a continuum between parallel and convergent evolution, while others maintain that despite some overlap, there are still important distinctions between the two. Convergent evolution_sentence_27

When the ancestral forms are unspecified or unknown, or the range of traits considered is not clearly specified, the distinction between parallel and convergent evolution becomes more subjective. Convergent evolution_sentence_28

For instance, the striking example of similar placental and marsupial forms is described by Richard Dawkins in The Blind Watchmaker as a case of convergent evolution, because mammals on each continent had a long evolutionary history prior to the extinction of the dinosaurs under which to accumulate relevant differences. Convergent evolution_sentence_29

At molecular level Convergent evolution_section_5

Proteins Convergent evolution_section_6

Protease active sites Convergent evolution_section_7

Main article: catalytic triad Convergent evolution_sentence_30

The enzymology of proteases provides some of the clearest examples of convergent evolution. Convergent evolution_sentence_31

These examples reflect the intrinsic chemical constraints on enzymes, leading evolution to converge on equivalent solutions independently and repeatedly. Convergent evolution_sentence_32

Serine and cysteine proteases use different amino acid functional groups (alcohol or thiol) as a nucleophile. Convergent evolution_sentence_33

In order to activate that nucleophile, they orient an acidic and a basic residue in a catalytic triad. Convergent evolution_sentence_34

The chemical and physical constraints on enzyme catalysis have caused identical triad arrangements to evolve independently more than 20 times in different enzyme superfamilies. Convergent evolution_sentence_35

Threonine proteases use the amino acid threonine as their catalytic nucleophile. Convergent evolution_sentence_36

Unlike cysteine and serine, threonine is a secondary alcohol (i.e. has a methyl group). Convergent evolution_sentence_37

The methyl group of threonine greatly restricts the possible orientations of triad and substrate, as the methyl clashes with either the enzyme backbone or the histidine base. Convergent evolution_sentence_38

Consequently, most threonine proteases use an N-terminal threonine in order to avoid such steric clashes. Convergent evolution_sentence_39

Several evolutionarily independent enzyme superfamilies with different protein folds use the N-terminal residue as a nucleophile. Convergent evolution_sentence_40

This commonality of active site but difference of protein fold indicates that the active site evolved convergently in those families. Convergent evolution_sentence_41

Cone snail and fish insulin Convergent evolution_section_8

Conus geographus produces a distinct form of insulin that is more similar to fish insulin protein sequences than to insulin from more closely related molluscs, suggesting convergent evolution. Convergent evolution_sentence_42

Na,K-ATPase and Insect resistance to cardenolides Convergent evolution_section_9

Many examples of convergent evolution exist in insects in terms of developing resistance at a molecular level to toxins. Convergent evolution_sentence_43

One well-characterized example is the evolution of amino acid substitutions at well-defined positions in the structure of the Na,K-ATPase α-subunit spanning 15 genera and 4 orders. Convergent evolution_sentence_44

The synergistic relationship between the Q111 and N122 substitutions are highlighted. Convergent evolution_sentence_45

Convergent evolution in this case does not depend on the type of selection or time frame in which it can occur, but has more to do with the co-evolutionary relationship causing a sort of soft selection between cardenolide-producing plants and the insects that prey on them. Convergent evolution_sentence_46

Nucleic acids Convergent evolution_section_10

Convergence occurs at the level of DNA and the amino acid sequences produced by translating structural genes into proteins. Convergent evolution_sentence_47

Studies have found convergence in amino acid sequences in echolocating bats and the dolphin; among marine mammals; between giant and red pandas; and between the thylacine and canids. Convergent evolution_sentence_48

Convergence has also been detected in a type of non-coding DNA, cis-regulatory elements, such as in their rates of evolution; this could indicate either positive selection or relaxed purifying selection. Convergent evolution_sentence_49

In animal morphology Convergent evolution_section_11

Bodyplans Convergent evolution_section_12

Swimming animals including fish such as herrings, marine mammals such as dolphins, and ichthyosaurs (of the Mesozoic) all converged on the same streamlined shape. Convergent evolution_sentence_50

A similar shape and swimming adaptations are even present in molluscs, such as Phylliroe. Convergent evolution_sentence_51

The fusiform bodyshape (a tube tapered at both ends) adopted by many aquatic animals is an adaptation to enable them to travel at high speed in a high drag environment. Convergent evolution_sentence_52

Similar body shapes are found in the earless seals and the eared seals: they still have four legs, but these are strongly modified for swimming. Convergent evolution_sentence_53

The marsupial fauna of Australia and the placental mammals of the Old World have several strikingly similar forms, developed in two clades, isolated from each other. Convergent evolution_sentence_54

The body and especially the skull shape of the thylacine (Tasmanian tiger or Tasmanian wolf) converged with those of Canidae such as the red fox, Vulpes vulpes. Convergent evolution_sentence_55

Convergent evolution_unordered_list_0

  • Convergence of marsupial and placental mammalsConvergent evolution_item_0_0
  • Convergent evolution_item_0_1
  • Convergent evolution_item_0_2
  • Convergent evolution_item_0_3

Echolocation Convergent evolution_section_13

As a sensory adaptation, echolocation has evolved separately in cetaceans (dolphins and whales) and bats, but from the same genetic mutations. Convergent evolution_sentence_56

Eyes Convergent evolution_section_14

Main article: Eye evolution Convergent evolution_sentence_57

One of the best-known examples of convergent evolution is the camera eye of cephalopods (such as squid and octopus), vertebrates (including mammals) and cnidaria (such as jellyfish). Convergent evolution_sentence_58

Their last common ancestor had at most a simple photoreceptive spot, but a range of processes led to the progressive refinement of camera eyes — with one sharp difference: the cephalopod eye is "wired" in the opposite direction, with blood and nerve vessels entering from the back of the retina, rather than the front as in vertebrates. Convergent evolution_sentence_59

As a result, cephalopods lack a blind spot. Convergent evolution_sentence_60

Flight Convergent evolution_section_15

Further information: Flying and gliding animals § Evolution and ecology of aerial locomotion Convergent evolution_sentence_61

Birds and bats have homologous limbs because they are both ultimately derived from terrestrial tetrapods, but their flight mechanisms are only analogous, so their wings are examples of functional convergence. Convergent evolution_sentence_62

The two groups have powered flight, evolved independently. Convergent evolution_sentence_63

Their wings differ substantially in construction. Convergent evolution_sentence_64

The bat wing is a membrane stretched across four extremely elongated fingers and the legs. Convergent evolution_sentence_65

The airfoil of the bird wing is made of feathers, strongly attached to the forearm (the ulna) and the highly fused bones of the wrist and hand (the carpometacarpus), with only tiny remnants of two fingers remaining, each anchoring a single feather. Convergent evolution_sentence_66

So, while the wings of bats and birds are functionally convergent, they are not anatomically convergent. Convergent evolution_sentence_67

Birds and bats also share a high concentration of cerebrosides in the skin of their wings. Convergent evolution_sentence_68

This improves skin flexibility, a trait useful for flying animals; other mammals have a far lower concentration. Convergent evolution_sentence_69

The extinct pterosaurs independently evolved wings from their fore- and hindlimbs, while insects have wings that evolved separately from different organs. Convergent evolution_sentence_70

Flying squirrels and sugar gliders are much alike in their body plans, with gliding wings stretched between their limbs, but flying squirrels are placental mammals while sugar gliders are marsupials, widely separated within the mammal lineage. Convergent evolution_sentence_71

Hummingbird hawk-moths and hummingbirds have evolved similar flight and feeding patterns. Convergent evolution_sentence_72

Insect mouthparts Convergent evolution_section_16

Insect mouthparts show many examples of convergent evolution. Convergent evolution_sentence_73

The mouthparts of different insect groups consist of a set of homologous organs, specialised for the dietary intake of that insect group. Convergent evolution_sentence_74

Convergent evolution of many groups of insects led from original biting-chewing mouthparts to different, more specialised, derived function types. Convergent evolution_sentence_75

These include, for example, the proboscis of flower-visiting insects such as bees and flower beetles, or the biting-sucking mouthparts of blood-sucking insects such as fleas and mosquitos. Convergent evolution_sentence_76

Opposable thumbs Convergent evolution_section_17

Opposable thumbs allowing the grasping of objects are most often associated with primates, like humans, monkeys, apes, and lemurs. Convergent evolution_sentence_77

Opposable thumbs also evolved in giant pandas, but these are completely different in structure, having six fingers including the thumb, which develops from a wrist bone entirely separately from other fingers. Convergent evolution_sentence_78

Primates Convergent evolution_section_18

Further information: Human skin color § Genetics of skin color variation Convergent evolution_sentence_79

Convergent evolution in humans includes blue eye colour and light skin colour. Convergent evolution_sentence_80

When humans migrated out of Africa, they moved to more northern latitudes with less intense sunlight. Convergent evolution_sentence_81

It was beneficial to them to reduce their skin pigmentation. Convergent evolution_sentence_82

It appears certain that there was some lightening of skin colour before European and East Asian lineages diverged, as there are some skin-lightening genetic differences that are common to both groups. Convergent evolution_sentence_83

However, after the lineages diverged and became genetically isolated, the skin of both groups lightened more, and that additional lightening was due to different genetic changes. Convergent evolution_sentence_84

Lemurs and humans are both primates. Convergent evolution_sentence_85

Ancestral primates had brown eyes, as most primates do today. Convergent evolution_sentence_86

The genetic basis of blue eyes in humans has been studied in detail and much is known about it. Convergent evolution_sentence_87

It is not the case that one gene locus is responsible, say with brown dominant to blue eye colour. Convergent evolution_sentence_88

However, a single locus is responsible for about 80% of the variation. Convergent evolution_sentence_89

In lemurs, the differences between blue and brown eyes are not completely known, but the same gene locus is not involved. Convergent evolution_sentence_90

In plants Convergent evolution_section_19

Carbon fixation Convergent evolution_section_20

While convergent evolution is often illustrated with animal examples, it has often occurred in plant evolution. Convergent evolution_sentence_91

For instance, C4 photosynthesis, one of the three major carbon-fixing biochemical processes, has arisen independently up to 40 times. Convergent evolution_sentence_92

About 7,600 plant species of angiosperms use C4 carbon fixation, with many monocots including 46% of grasses such as maize and sugar cane, and dicots including several species in the Chenopodiaceae and the Amaranthaceae. Convergent evolution_sentence_93

Fruits Convergent evolution_section_21

A good example of convergence in plants is the evolution of edible fruits such as apples. Convergent evolution_sentence_94

These pomes incorporate (five) carpels and their accessory tissues forming the apple's core, surrounded by structures from outside the botanical fruit, the receptacle or hypanthium. Convergent evolution_sentence_95

Other edible fruits include other plant tissues; for example, the fleshy part of a tomato is the walls of the pericarp. Convergent evolution_sentence_96

This implies convergent evolution under selective pressure, in this case the competition for seed dispersal by animals through consumption of fleshy fruits. Convergent evolution_sentence_97

Seed dispersal by ants (myrmecochory) has evolved independently more than 100 times, and is present in more than 11,000 plant species. Convergent evolution_sentence_98

It is one of the most dramatic examples of convergent evolution in biology. Convergent evolution_sentence_99

Carnivory Convergent evolution_section_22

Carnivory has evolved multiple times independently in plants in widely separated groups. Convergent evolution_sentence_100

In three species studied, Cephalotus follicularis, Nepenthes alata and Sarracenia purpurea, there has been convergence at the molecular level. Convergent evolution_sentence_101

Carnivorous plants secrete enzymes into the digestive fluid they produce. Convergent evolution_sentence_102

By studying phosphatase, glycoside hydrolase, glucanase, RNAse and chitinase enzymes as well as a pathogenesis-related protein and a thaumatin-related protein, the authors found many convergent amino acid substitutions. Convergent evolution_sentence_103

These changes were not at the enzymes' catalytic sites, but rather on the exposed surfaces of the proteins, where they might interact with other components of the cell or the digestive fluid. Convergent evolution_sentence_104

The authors also found that homologous genes in the non-carnivorous plant Arabidopsis thaliana tend to have their expression increased when the plant is stressed, leading the authors to suggest that stress-responsive proteins have often been co-opted in the repeated evolution of carnivory. Convergent evolution_sentence_105

Methods of inference Convergent evolution_section_23

Phylogenetic reconstruction and ancestral state reconstruction proceed by assuming that evolution has occurred without convergence. Convergent evolution_sentence_106

Convergent patterns may, however, appear at higher levels in a phylogenetic reconstruction, and are sometimes explicitly sought by investigators. Convergent evolution_sentence_107

The methods applied to infer convergent evolution depend on whether pattern-based or process-based convergence is expected. Convergent evolution_sentence_108

Pattern-based convergence is the broader term, for when two or more lineages independently evolve patterns of similar traits. Convergent evolution_sentence_109

Process-based convergence is when the convergence is due to similar forces of natural selection. Convergent evolution_sentence_110

Pattern-based measures Convergent evolution_section_24

Earlier methods for measuring convergence incorporate ratios of phenotypic and phylogenetic distance by simulating evolution with a Brownian motion model of trait evolution along a phylogeny. Convergent evolution_sentence_111

More recent methods also quantify the strength of convergence. Convergent evolution_sentence_112

One drawback to keep in mind is that these methods can confuse long-term stasis with convergence due to phenotypic similarities. Convergent evolution_sentence_113

Stasis occurs when there is little evolutionary change among taxa. Convergent evolution_sentence_114

Distance-based measures assess the degree of similarity between lineages over time. Convergent evolution_sentence_115

Frequency-based measures assess the number of lineages that have evolved in a particular trait space. Convergent evolution_sentence_116

Process-based measures Convergent evolution_section_25

Methods to infer process-based convergence fit models of selection to a phylogeny and continuous trait data to determine whether the same selective forces have acted upon lineages. Convergent evolution_sentence_117

This uses the Ornstein-Uhlenbeck (OU) process to test different scenarios of selection. Convergent evolution_sentence_118

Other methods rely on an a priori specification of where shifts in selection have occurred. Convergent evolution_sentence_119

See also Convergent evolution_section_26

Convergent evolution_unordered_list_1

  • Incomplete lineage sorting – Characteristic of phylogenetic analysis: the presence of multiple alleles in ancestral populations might lead to the impression that convergent evolution has occurred.Convergent evolution_item_1_4
  • Carcinisation – Evolution of a non-crab-like crustacean into a crab-like formConvergent evolution_item_1_5

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: evolution.