64-488: Conosa is a grouping of Amoebozoa . It is subdivided into three groups: Archamoeba , Variosea and Mycetozoa . In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa (= Eumycetozoa). Conosa includes the species Dictyostelium discoideum , a social amoeba, and Entamoeba histolytica , a human pathogen , among others. Conosa are morphologically defined by
128-444: A Brownian motion model of trait evolution along a phylogeny. More recent methods also quantify the strength of convergence. One drawback to keep in mind is that these methods can confuse long-term stasis with convergence due to phenotypic similarities. Stasis occurs when there is little evolutionary change among taxa. Distance-based measures assess the degree of similarity between lineages over time. Frequency-based measures assess
192-428: A nucleophile . In order to activate that nucleophile, they orient an acidic and a basic residue in a catalytic triad . The chemical and physical constraints on enzyme catalysis have caused identical triad arrangements to evolve independently more than 20 times in different enzyme superfamilies . Threonine proteases use the amino acid threonine as their catalytic nucleophile . Unlike cysteine and serine, threonine
256-410: A "monopodial" form, with the entire cell functioning as a single pseudopod. Large pseudopods may produce numerous clear projections called subpseudopodia (or determinate pseudopodia ), which are extended to a certain length and then retracted, either for the purpose of locomotion or food intake. A cell may also form multiple indeterminate pseudopodia, through which the entire contents of the cell flow in
320-401: A conical microtubular structure, and have been found to be monophyletic. The Conosa group was first proposed by Thomas Cavalier-Smith in 1998 as a subphylum of Amoebozoa . Cavalier-Smith originally separated this group into 2 infraphyla: Archamoebae and Mycetozoa . Notable characteristics of these two groups are that Mycetozoa are free living, while Archamoebae are amitochondrial. This clade
384-575: A high concentration of cerebrosides in the skin of their wings. This improves skin flexibility, a trait useful for flying animals; other mammals have a far lower concentration. The extinct pterosaurs independently evolved wings from their fore- and hindlimbs, while insects have wings that evolved separately from different organs. Flying squirrels and sugar gliders are much alike in their mammalian body plans, with gliding wings stretched between their limbs, but flying squirrels are placentals while sugar gliders are marsupials, widely separated within
448-512: A high-level taxon , named Amorphea . Amoebozoa includes many of the best-known amoeboid organisms, such as Chaos , Entamoeba , Pelomyxa and the genus Amoeba itself. Species of Amoebozoa may be either shelled (testate) or naked, and cells may possess flagella . Free-living species are common in both salt and freshwater as well as soil, moss and leaf litter. Some live as parasites or symbionts of other organisms, and some are known to cause disease in humans and other organisms. While
512-643: A molecular level to toxins. One well-characterized example is the evolution of resistance to cardiotonic steroids (CTSs) via amino acid substitutions at well-defined positions of the α-subunit of Na ,K -ATPase (ATPalpha). Variation in ATPalpha has been surveyed in various CTS-adapted species spanning six insect orders. Among 21 CTS-adapted species, 58 (76%) of 76 amino acid substitutions at sites implicated in CTS resistance occur in parallel in at least two lineages. 30 of these substitutions (40%) occur at just two sites in
576-516: A more suitable name for a clade of approximately the same composition, a sister group to the Diaphoretickes . More recent work places the members of Amorphea together with the malawimonids and collodictyonids in a proposed clade called Opimoda, which comprises one of two major lineages diverging at the root of the eukaryote tree of life, the other being Diphoda . Traditionally all amoebozoa with lobose pseudopods were grouped together in
640-568: A phylogenetic reconstruction, and are sometimes explicitly sought by investigators. The methods applied to infer convergent evolution depend on whether pattern-based or process-based convergence is expected. Pattern-based convergence is the broader term, for when two or more lineages independently evolve patterns of similar traits. Process-based convergence is when the convergence is due to similar forces of natural selection . Earlier methods for measuring convergence incorporate ratios of phenotypic and phylogenetic distance by simulating evolution with
704-400: A posterior bulb called a uroid, which may serve to accumulate waste, periodically detaching from the rest of the cell. When food is scarce, most species can form cysts , which may be carried aerially and introduce them to new environments. In slime moulds, these structures are called spores, and form on stalked structures called fruiting bodies or sporangia . Mixotrophic species living in
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#1732787832847768-501: A steadily decreasing probability of retaining potential functionality over time. 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. 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. Some scientists have argued that there
832-543: A symbiotic relationship with microalgae of the genus Chlorella , which lives inside the cytoplasm of their host, have been found in Arcellinida and Mayorella . The majority of Amoebozoa lack flagella and more generally do not form microtubule -supported structures except during mitosis . However, flagella do occur among the Archamoebae , and many slime moulds produce biflagellate gametes . The flagellum
896-438: A trait presently identified with at least primates , corvids , and cetaceans . In cladistics, a homoplasy is a trait shared by two or more taxa for any reason other than that they share a common ancestry. 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 . Homoplastic traits caused by convergence are therefore, from
960-421: Is divergent evolution , where related species evolve different traits. 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 . Many instances of convergent evolution are known in plants , including
1024-427: Is a secondary alcohol (i.e. has a methyl group). 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. Consequently, most threonine proteases use an N-terminal threonine in order to avoid such steric clashes . Several evolutionarily independent enzyme superfamilies with different protein folds use
1088-443: Is a continuum between parallel and convergent evolution, while others maintain that despite some overlap, there are still important distinctions between the two. 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. For instance, the striking example of similar placental and marsupial forms
1152-423: Is a large and diverse group, but certain features are common to many of its members. The amoebozoan cell is typically divided into a granular central mass, called endoplasm , and a clear outer layer, called ectoplasm. During locomotion, the endoplasm flows forwards and the ectoplasm runs backwards along the outside of the cell. In motion, many amoebozoans have a clearly defined anterior and posterior and may assume
1216-463: Is a membrane stretched across four extremely elongated fingers and the legs. 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. So, while the wings of bats and birds are functionally convergent, they are not anatomically convergent. Birds and bats also share
1280-673: 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. The enzymology of proteases provides some of the clearest examples of convergent evolution. These examples reflect the intrinsic chemical constraints on enzymes, leading evolution to converge on equivalent solutions independently and repeatedly. Serine and cysteine proteases use different amino acid functional groups (alcohol or thiol) as
1344-486: Is generally anchored by a cone of microtubules, suggesting a close relationship to the opisthokonts . The mitochondria in amoebozoan cells characteristically have branching tubular cristae. However, among the Archamoebae , which are adapted to anoxic or microaerophilic habitats, mitochondria have been lost. It appears (based on molecular genetics) that the members of Amoebozoa form a sister group to animals and fungi, diverging from this lineage after it had split from
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#17327878328471408-427: Is morphologically defined by their complex microtubular skeleton that forms a partial or complete cone. They have a monolayer of microtubules that surround at least some of the anterior end of the cell and diverge into a cone shape towards the nucleus at the posterior end. This cone of microtubules usually starts at a single centriole and extends towards the nucleus. They also have a lateral microtubular ribbon towards
1472-542: Is responsible, say with brown dominant to blue eye colour . However, a single locus is responsible for about 80% of the variation. In lemurs, the differences between blue and brown eyes are not completely known, but the same gene locus is not involved. While most plant species are perennial , about 6% follow an annual life cycle, living for only one growing season. The annual life cycle independently emerged in over 120 plant families of angiosperms. The prevalence of annual species increases under hot-dry summer conditions in
1536-409: Is the camera eye of cephalopods (such as squid and octopus), vertebrates (including mammals) and cnidarians (such as jellyfish). 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
1600-457: Is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. The cladistic term for the same phenomenon is homoplasy . The recurrent evolution of flight is a classic example, as flying insects , birds , pterosaurs , and bats have independently evolved
1664-763: Is usually ranked as a phylum within either the kingdom Protista or the kingdom Protozoa . In the classification favored by the International Society of Protistologists, it is retained as an unranked " supergroup " within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade . Modern studies of eukaryotic phylogenetic trees identify it as the sister group to Opisthokonta , another major clade which contains both fungi and animals as well as several other clades comprising some 300 species of unicellular eukaryotes. Amoebozoa and Opisthokonta are sometimes grouped together in
1728-536: The Chenopodiaceae and the Amaranthaceae . Fruits with a wide variety of structural origins have converged to become edible. Apples are pomes with five carpels ; their accessory tissues form the apple's core, surrounded by structures from outside the botanical fruit, the receptacle or hypanthium . Other edible fruits include other plant tissues; the fleshy part of a tomato is the walls of
1792-601: The cytoplasm , both of which are not seen in Lobosa. While morphological characteristics like pseudopodia and body shape, flagella, and cytoplasm properties have not been regarded as convincing taxonomic suggestions, emerging sequencing data is being used to support Conosa’s monophyly. A study using several hundred phylogenetic markers of 30 species found Conosa to be monophyletic as representatives of Mycetozoa, Entamoebidae, and Pelobionta grouped together using several amino acid sequencing analysis methods. The monophyly of Conosa and
1856-619: The pericarp . This implies convergent evolution under selective pressure, in this case the competition for seed dispersal by animals through consumption of fleshy fruits. Seed dispersal by ants ( myrmecochory ) has evolved independently more than 100 times, and is present in more than 11,000 plant species. It is one of the most dramatic examples of convergent evolution in biology. Carnivory has evolved multiple times independently in plants in widely separated groups. In three species studied, Cephalotus follicularis , Nepenthes alata and Sarracenia purpurea , there has been convergence at
1920-446: 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 . Opposable thumbs allowing the grasping of objects are most often associated with primates , like humans and other apes, monkeys, and lemurs. Opposable thumbs also evolved in giant pandas , but these are completely different in structure, having six fingers including
1984-738: The Archamoebea infraphyla was also supported by cDNA sequencing of 17 Amoebozoans. However, the monophyly of Conosa is not entirely supported. For example, another study using 7 protein coding genes did not find Conosa to be monophyletic due to members of Lobosa sharing a phylogenetic branch with the Conosan lineage Variosea. This same study did find all three Conosan lineages to be monophyletic. Flabellinia Centramoebia Corycidia Echinamoebia Elardia Cutosea Archamoebea Variosea Dictyostelea Ceratiomyxea Myxogastrea Opisthokonta The last common ancestor of Conosa
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2048-672: The Lobosa are paraphyletic: Conosa is sister of the Cutosea. Centramoebida Himatismenida Himatismenida Thecamoebida Dermamoebida Vannellida Dactylopodida Trichosida Microcoryciidae Echinamoebida Leptomyxida Euamoebida Arcellinida Squamocutida Entamoebida Pelobiontida Phalansteriida Flamellidae Ramamoebida Profiliida Fractovitellida Acytosteliales Dictyosteliida Ceratiomyxida Protosporangiida Cribrariales Reticulariales Liceida Trichiida Convergent evolution Convergent evolution
2112-575: The Mesozoic ) all converged on the same streamlined shape. A similar shape and swimming adaptations are even present in molluscs, such as Phylliroe . 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. 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. The marsupial fauna of Australia and
2176-523: The N-terminal residue as a nucleophile. This commonality of active site but difference of protein fold indicates that the active site evolved convergently in those families. 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, though with the possibility of horizontal gene transfer . Distant homologues of
2240-471: The back of the retina, rather than the front as in vertebrates. As a result, vertebrates have a blind spot . 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. The two groups have independently evolved their own means of powered flight. Their wings differ substantially in construction. The bat wing
2304-449: The cell surface. Conosa can exist as aggregate aerobes with mitochondria and also as solitary anaerobes with no mitochondria or peroxisomes . There are mitochondriate and amitochondriate members, as well as free living and parasitic representatives. Mitochondria reduction could be a result of transitions to a parasitic lifestyle, as is seen in the amitochondral human parasite Entamoeba histolytica. Conosa are separated from Lobosa ,
2368-502: The class Lobosea , placed with other amoeboids in the phylum Sarcodina or Rhizopoda , but these were considered to be unnatural groups. Structural and genetic studies identified the percolozoans and several archamoebae as independent groups. In phylogenies based on rRNA their representatives were separate from other amoebae, and appeared to diverge near the base of eukaryotic evolution, as did most slime molds. However, revised trees by Cavalier-Smith and Chao in 1996 suggested that
2432-481: The classic Lobosea: non-flagellated amoebae with blunt, lobose pseudopods ( Amoeba , Acanthamoeba, Arcella, Difflugia etc. ). The latter is made up of both amoeboid and flagellated cells, characteristically with more pointed or slightly branching subpseudopodia (Archamoebae and the Mycetozoan slime molds). From older studies by Cavalier-Smith, Chao & Lewis 2016 and Silar 2016. Also recent phylogeny indicates
2496-513: The complete proteomic content of 23 eukaryotic genomes found that representative members of Mycetozoa and Archamoebae do share a common ancestor, and their divergence occurred almost as long ago as the split of fungi and animals . Amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists , often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae . In traditional classification schemes, Amoebozoa
2560-406: The direction of locomotion. These are more or less tubular and are mostly filled with granular endoplasm. The cell mass flows into a leading pseudopod, and the others ultimately retract, unless the organism changes direction. While most amoebozoans are "naked," like the familiar Amoeba and Chaos , or covered with a loose coat of minute scales, like Cochliopodium and Korotnevella , members of
2624-437: The dolphin; among marine mammals; between giant and red pandas; and between the thylacine and canids. 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 . Swimming animals including fish such as herrings , marine mammals such as dolphins , and ichthyosaurs ( of
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2688-617: The exposed surfaces of the proteins, where they might interact with other components of the cell or the digestive fluid. 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. Phylogenetic reconstruction and ancestral state reconstruction proceed by assuming that evolution has occurred without convergence. Convergent patterns may, however, appear at higher levels in
2752-480: The four species-rich families of annuals ( Asteraceae , Brassicaceae , Fabaceae , and Poaceae ), indicating that the annual life cycle is adaptive. C 4 photosynthesis , one of the three major carbon-fixing biochemical processes, has arisen independently up to 40 times . About 7,600 plant species of angiosperms use C 4 carbon fixation, with many monocots including 46% of grasses such as maize and sugar cane , and dicots including several species in
2816-464: The largest protozoa. The well-known species Amoeba proteus , which may reach 800 μm in length, is often studied in schools and laboratories as a representative cell or model organism , partly because of its convenient size. Multinucleate amoebae like Chaos and Pelomyxa may be several millimetres in length, and some multicellular amoebozoa, such as the "dog vomit" slime mold Fuligo septica , can cover an area of several square meters. Amoebozoa
2880-407: The lineages diverged and became genetically isolated, the skin of both groups lightened more, and that additional lightening was due to different genetic changes. Lemurs and humans are both primates. Ancestral primates had brown eyes, as most primates do today. The genetic basis of blue eyes in humans has been studied in detail and much is known about it. It is not the case that one gene locus
2944-424: The majority of amoebozoan species are unicellular, the group also includes several clades of slime molds , which have a macroscopic, multicellular stage of life during which individual amoeboid cells remain together after multiple cell division to form a macroscopic plasmodium or, in cellular slime molds, aggregate to form one. Amoebozoa vary greatly in size. Some are only 10–20 μm in diameter, while others are among
3008-516: The mammal lineage from the placentals. Hummingbird hawk-moths and hummingbirds have evolved similar flight and feeding patterns. Insect mouthparts show many examples of convergent evolution. The mouthparts of different insect groups consist of a set of homologous organs, specialised for the dietary intake of that insect group. Convergent evolution of many groups of insects led from original biting-chewing mouthparts to different, more specialised, derived function types. These include, for example,
3072-454: The metal ion transporters ZIP in land plants and chlorophytes have converged in structure, likely to take up Fe efficiently. The IRT1 proteins from Arabidopsis thaliana and rice have extremely different amino acid sequences from Chlamydomonas ' s IRT1, but their three-dimensional structures are similar, suggesting convergent evolution. Many examples of convergent evolution exist in insects in terms of developing resistance at
3136-405: The molecular level. Carnivorous plants secrete enzymes into the digestive fluid they produce. 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. These changes were not at the enzymes' catalytic sites, but rather on
3200-468: The name "unikonts" (formally, Unikonta) for this branch, whose members were believed to have been descended from a common ancestor possessing a single emergent flagellum rooted in one basal body . However, while the close relationship between Amoebozoa and Opisthokonta is robustly supported, recent work has shown that the hypothesis of a uniciliate ancestor is probably false. In their Revised Classification of Eukaryotes (2012), Adl et al. proposed Amorphea as
3264-629: The order Arcellinida form rigid shells, or tests , equipped with a single aperture through which the pseudopods emerge. Arcellinid tests may be secreted from organic materials, as in Arcella , or built up from collected particles cemented together, as in Difflugia . In all amoebozoa, the primary mode of nutrition is phagocytosis , in which the cell surrounds potential food particles with its pseudopods, sealing them into vacuoles within which they may be digested and absorbed. Some amoebozoans have
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#17327878328473328-482: The other Amoebozoa subphylum, by morphological characteristics and genomic differences. Conosa have both amoeboid and flagellate forms or stages and more pointed pseudopodia with branches. In contrast, Lobosa are entirely amoeboid with broad pseudopodia. Conosa's flagella are artifacts of their ancestral conditions and are seen in trophic and swarm cell phases. Flagellate Conosa have a cone-shaped microtubular skeleton, and non-ciliate forms contain extensive microtubes in
3392-404: The other groups, as illustrated below in a simplified diagram: Loukozoa [REDACTED] CRuMs [REDACTED] Amoebozoa Breviata [REDACTED] Apusomonadida [REDACTED] Fungi [REDACTED] Animalia [REDACTED] Strong similarities between Amoebozoa and Opisthokonts lead to the hypothesis that they form a distinct clade. Thomas Cavalier-Smith proposed
3456-479: The placental mammals of the Old World have several strikingly similar forms, developed in two clades, isolated from each other. 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 . As a sensory adaptation, echolocation has evolved separately in cetaceans (dolphins and whales) and bats, but from
3520-401: The point of view of cladistics, confounding factors which could lead to an incorrect analysis. 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. Such a re-emerged trait is called an atavism . From a mathematical standpoint, an unused gene ( selectively neutral ) has
3584-404: The protein (positions 111 and 122). CTS-adapted species have also recurrently evolved neo-functionalized duplications of ATPalpha, with convergent tissue-specific expression patterns. Convergence occurs at the level of DNA and the amino acid sequences produced by translating structural genes into proteins . Studies have found convergence in amino acid sequences in echolocating bats and
3648-685: The remaining lobosans do form a monophyletic group, to which the Archamoebae and Mycetozoa were closely related, although the percolozoans were not. Subsequently, they emended the phylum Amoebozoa to include both the subphylum Lobosa and a new subphylum Conosa , comprising the Archamoebae and the Mycetozoa . Recent molecular genetic data appear to support this primary division of the Amoebozoa into Lobosa and Conosa. The former, as defined by Cavalier-Smith and his collaborators, consists largely of
3712-462: The repeated development of C 4 photosynthesis , seed dispersal by fleshy fruits adapted to be eaten by animals, and carnivory . In morphology, analogous traits arise when different species live in similar ways and/or a similar environment, and so face the same environmental factors. When occupying similar ecological niches (that is, a distinctive way of life) similar problems can lead to similar solutions. The British anatomist Richard Owen
3776-401: The same conditions were encountered again, evolution could take a very different course." 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,
3840-473: The same genetic mutations. The Gymnotiformes of South America and the Mormyridae of Africa independently evolved passive electroreception (around 119 and 110 million years ago, respectively). Around 20 million years after acquiring that ability, both groups evolved active electrogenesis , producing weak electric fields to help them detect prey. One of the best-known examples of convergent evolution
3904-554: The thumb, which develops from a wrist bone entirely separately from other fingers. Convergent evolution in humans includes blue eye colour and light skin colour. When humans migrated out of Africa , they moved to more northern latitudes with less intense sunlight. It was beneficial to them to reduce their skin pigmentation . 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. However, after
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#17327878328473968-413: The useful capacity of flight. 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. Bird, bat, and pterosaur wings are analogous structures, but their forelimbs are homologous, sharing an ancestral state despite serving different functions. The opposite of convergence
4032-587: Was likely an aerobic protist with anterior and recurrent flagellum. It likely had mitochondria, while mitochondrial reduction has resulted in both mitochondriate and amitochondriate members today. The ancestral biflagellate condition is seen in some extant Conosa forms. In some Archamoebae, the posterior flagella and its related cytoskeleton has been lost, and others have lost the entire flagellar system. The conical microtubular skeleton convergently evolved in Archamoebae and Variosea, but not in Mycetozoa. A study of
4096-408: Was the first to identify the fundamental difference between analogies and homologies . 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 . In his 1989 book Wonderful Life , Stephen Jay Gould argued that if one could "rewind the tape of life [and]
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