Parallel evolution
Encyclopedia
Parallel evolution is the development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clade
s.
For a particular trait, proceeding in each of two lineages from a specified ancestor to a later descendant, parallel and convergent
evolutionary trends can be strictly defined and clearly distinguished from one another.
When both descendants are similar in a particular respect, evolution is defined as parallel if the ancestors considered were also similar, and convergent if they were not.
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 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. Stephen Jay Gould
describes many of the same examples as parallel evolution starting from the common ancestor of all marsupials and placentals. Many evolved similarities can be described in concept as parallel evolution from a remote ancestor, with the exception of those where quite different structures are co-opted to a similar function. For example, consider Mixotricha paradoxa
, an eukaryotic
microbe which has assembled a system of rows of apparent cilia and basal bodies
closely resembling that of ciliate
s but which are actually smaller symbiont microorganisms, or the differently oriented tails of fish and whales. Conversely, any case in which lineages do not evolve together at the same time in the same ecospace might be described as convergent evolution at some point in time.
The definition of a trait is crucial in deciding whether a change is seen as divergent, or as parallel or convergent. In the image above, note that since serine
and threonine
possess similar structures with an alcohol side chain, the example marked "divergent" would be termed "parallel" if the amino acids were grouped by similarity instead of being considered individually. As another example, if genes in two species independently become restricted to the same region of the animals through regulation by a certain transcription factor, this may be described as a case of parallel evolution - but examination of the actual DNA sequence will probably show only divergent changes in individual basepair positions, since a new transcription factor binding site can be added in a wide range of places within the gene with similar effect.
A similar situation occurs considering the homology
of morphological structures. For example, many insects possess two pairs of flying wings. In beetles, the first pair of wings is hardened into wing covers with little role in flight, while in flies the second pair of wings is condensed into small halteres
used for balance. If the two pairs of wings are considered as interchangeable, homologous structures, this may be described as a parallel reduction in the number of wings, but otherwise the two changes are each divergent changes in one pair of wings.
Similar to convergent evolution, evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems, but not at the same time (dorsal fin
s of shark
s and ichthyosaur
s).
s, the placentals and marsupial
s, which have followed independent evolutionary pathways following the break-up of land-masses such as Gondwanaland roughly 100 million years ago. In South America
, marsupials and placentals shared the ecosystem (prior to the Great American Interchange
); in Australia
, marsupials prevailed; and in the Old World the placentals won out. However, in all these localities mammals were small and filled only limited places in the ecosystem until the mass extinction of dinosaurs sixty-five million years later. At this time, mammals on all three landmasses began to take on a much wider variety of forms and roles. While some forms were unique to each environment, surprisingly similar animals have often emerged in two or three of the separated continents. Examples of these include the litopterns
and horse
s, whose legs are difficult to distinguish; the European sabre-toothed cat (Machairodontinae
) and the South American marsupial sabre-tooth (Thylacosmilus
); the Tasmanian wolf and the European wolf; likewise marsupial and placental moles
, flying squirrels
, and (arguably) mice
.
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s.
Parallel vs. convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
evolutionary trends can be strictly defined and clearly distinguished from one another.
When both descendants are similar in a particular respect, evolution is defined as parallel if the ancestors considered were also similar, and convergent if they were not.
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 is described by Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
in The Blind Watchmaker
The Blind Watchmaker
The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design is a 1986 book by Richard Dawkins in which he presents an explanation of, and argument for, the theory of evolution by means of natural selection. He also presents arguments to refute certain criticisms made on...
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. Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
describes many of the same examples as parallel evolution starting from the common ancestor of all marsupials and placentals. Many evolved similarities can be described in concept as parallel evolution from a remote ancestor, with the exception of those where quite different structures are co-opted to a similar function. For example, consider Mixotricha paradoxa
Mixotricha paradoxa
Mixotricha paradoxa is a species of protozoan that lives inside the termite species Mastotermes darwiniensis and has multiple bacterial symbionts. The name, given by the Australian biologist J.L. Sutherland, who first described Mixotricha in 1933,. means “the paradoxical being with mixed-up...
, an eukaryotic
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
microbe which has assembled a system of rows of apparent cilia and basal bodies
Basal body
A basal body is an organelle formed from a centriole, and a short cylindrical array of microtubules. It is found at the base of a eukaryotic undulipodium and serves as a nucleation site for the growth of the axoneme microtubules...
closely resembling that of ciliate
Ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...
s but which are actually smaller symbiont microorganisms, or the differently oriented tails of fish and whales. Conversely, any case in which lineages do not evolve together at the same time in the same ecospace might be described as convergent evolution at some point in time.
The definition of a trait is crucial in deciding whether a change is seen as divergent, or as parallel or convergent. In the image above, note that since serine
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
and threonine
Threonine
Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...
possess similar structures with an alcohol side chain, the example marked "divergent" would be termed "parallel" if the amino acids were grouped by similarity instead of being considered individually. As another example, if genes in two species independently become restricted to the same region of the animals through regulation by a certain transcription factor, this may be described as a case of parallel evolution - but examination of the actual DNA sequence will probably show only divergent changes in individual basepair positions, since a new transcription factor binding site can be added in a wide range of places within the gene with similar effect.
A similar situation occurs considering the homology
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
of morphological structures. For example, many insects possess two pairs of flying wings. In beetles, the first pair of wings is hardened into wing covers with little role in flight, while in flies the second pair of wings is condensed into small halteres
Halteres
Halteres are small knobbed structures modified from the hind wings in some two-winged insects. They are flapped rapidly and function as gyroscopes, informing the insect about rotation of the body during flight....
used for balance. If the two pairs of wings are considered as interchangeable, homologous structures, this may be described as a parallel reduction in the number of wings, but otherwise the two changes are each divergent changes in one pair of wings.
Similar to convergent evolution, evolutionary relay describes how independent species acquire similar characteristics through their evolution in similar ecosystems, but not at the same time (dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s of shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s and ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
s).
Parallel speciation
Defined as the repeated independent evolution of the same reproductive isolating mechanism (Schluter and Nagel 1995). An example of this may occur when a species colonizes several new areas which are isolated from, but environmentally similar to, each other. Similar selective pressures in these environments result in parallel evolution among the traits that confer reproductive isolation.Examples
- Coloration that serves as a warning to predators and for mating displays have evolved in many different species.
- In the plant kingdom, the most familiar examples of parallel evolution are the forms of leavesLeafA leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
, where very similar patterns have appeared again and again in separate genera and families. - In butterfliesButterflyA butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured...
, many close similarities are found in the patterns of wing colouration, both within and between families. - Old and New world porcupinePorcupinePorcupines are rodents with a coat of sharp spines, or quills, that defend or camouflage them from predators. They are indigenous to the Americas, southern Asia, and Africa. Porcupines are the third largest of the rodents, behind the capybara and the beaver. Most porcupines are about long, with...
s shared a common ancestor, both evolved strikingly similar quill structures; this is also an example of convergent evolutionConvergent evolutionConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
as similar structures evolved in hedgehogHedgehogA hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand . There are no hedgehogs native to Australia, and no living species native to the Americas...
s, echidnaEchidnaEchidnas , also known as spiny anteaters, belong to the family Tachyglossidae in the monotreme order of egg-laying mammals. There are four extant species, which, together with the platypus, are the only surviving members of that order and are the only extant mammals that lay eggs...
s and tenrecs. - Contemporaneous evolution of the extinct browsing-horsesEvolution of the horseThe evolution of the horse pertains to the phylogenetic ancestry of the modern horse from the small dog-sized, forest-dwelling Hyracotherium over geologic time scales...
and extinct paleotheresPalaeotheriumPalaeotherium is an extinct genus of primitive perissodactyl ungulate. George Cuvier originally described them as being a kind of tapir, and as such, Palaeotherium is popularly reconstructed as a tapir-like animal...
both of which shared the same environmental space. - Some extinct Archosaurs evolved an upright posture and likely were warm-blooded. These two characteristics are also found in most mammals. Interestingly, modern crocodiles have a four chambered heart and a crurotarsalCrurotarsalA crurotarsal joint is one that’s situated between the bones of crus, i.e. shin and the proximal tarsal bones, i.e. astragalus and calcaneum....
, the latter being also a characteristic of therian mammals. - The extinctExtinctionIn biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
pterosaurs and the birdBirdBirds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s both evolved wings as well as a distinct beak, but not from a recent common ancestor. - Internal fertilizationInternal fertilizationIn mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...
has evolved independently in sharkSharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, some amphibians and amniotes. - The PatagiumPatagium*In bats, the skin forming the surface of the wing. It is an extension of the skin of the abdomen that runs to the tip of each digit, uniting the forelimb with the body.*The patagium of a bat has four distinct parts:...
is a fleshy membrane that is found in gliding mammals such as: flying lemurs, flying squirrels, sugar gliders and the extinct Volaticotherium. These mammals acquired the patagiumPatagium*In bats, the skin forming the surface of the wing. It is an extension of the skin of the abdomen that runs to the tip of each digit, uniting the forelimb with the body.*The patagium of a bat has four distinct parts:...
independently. - PyrotheriaPyrotheriaPyrotheria is an order of extinct meridiungulate mammals. These mastodon-like ungulates include the genera Baguatherium, Carolozittelia, Colombitherium, Gryphodon, Propyrotherium, Proticia, and Pyrotherium....
ns have evolved a body plan similar to proboscideaProboscideaProboscidea is a taxonomic order containing one living family, Elephantidae, and several extinct families. This order was first described by J. Illiger in 1881 and encompasses the trunked mammals...
ns. - The eye of the octopus has the same complicated structure as the human eye. As a result, it is often substituted in studies of the eye when using a human eye would be inappropriate. As the two species diverged at the time animals evolved into vertebrates and invertabrates this is extraordinary.
Parallel evolution between marsupials and placentals
One of the most spectacular examples of parallel evolution is provided by the two main branches of the mammalMammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s, the placentals and marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s, which have followed independent evolutionary pathways following the break-up of land-masses such as Gondwanaland roughly 100 million years ago. In South America
Neotropic
In biogeography, the Neotropic or Neotropical zone is one of the eight terrestrial ecozones. This ecozone includes South and Central America, the Mexican lowlands, the Caribbean islands, and southern Florida, because these regions share a large number of plant and animal groups.It is sometimes used...
, marsupials and placentals shared the ecosystem (prior to the Great American Interchange
Great American Interchange
The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...
); in Australia
Australia (continent)
Australia is the world's smallest continent, comprising the mainland of Australia and proximate islands including Tasmania, New Guinea, the Aru Islands and Raja Ampat Islands...
, marsupials prevailed; and in the Old World the placentals won out. However, in all these localities mammals were small and filled only limited places in the ecosystem until the mass extinction of dinosaurs sixty-five million years later. At this time, mammals on all three landmasses began to take on a much wider variety of forms and roles. While some forms were unique to each environment, surprisingly similar animals have often emerged in two or three of the separated continents. Examples of these include the litopterns
Litopterna
Litopterna is an extinct order of fossil hoofed mammals from the Tertiary period that displays toe reduction. Three-toed, and even a one-toed horselike form developed....
and horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, whose legs are difficult to distinguish; the European sabre-toothed cat (Machairodontinae
Machairodontinae
Machairodontinae is an extinct carnivoran mammal subfamily of Felidae endemic to Asia, Africa, North America, South America, and Europe from the Miocene to Pleistocene living from c. 23 Ma until c...
) and the South American marsupial sabre-tooth (Thylacosmilus
Thylacosmilus
Thylacosmilus was a genus of sabre-toothed metatherian predators that first appeared during the Miocene. Remains of the animal have been found in parts of South America, primarily Argentina...
); the Tasmanian wolf and the European wolf; likewise marsupial and placental moles
Marsupial mole
Marsupial moles is a family of marsupials of the order Notoryctemorphia, consisting of only two extant species:* Notoryctes typhlops * Notoryctes caurinus ...
, flying squirrels
Sugar Glider
The sugar glider is a small gliding possum originating from the marsupial family.The sugar glider is native to eastern and northern mainland Australia and is also native to New Guinea and the Bismarck Archipelago.- Habitat :Sugar gliders can be found all throughout the northern and eastern parts of...
, and (arguably) mice
Antechinus
Antechinus is a genus of dasyurid marsupial that is indigenous to Australia and New Guinea. The majority of Antechinus species occur in Australia and only two species have been described in New Guinea...
.
External links
See also
- Convergent evolutionConvergent evolutionConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
- Evolutionary relay
- Homology (biology)Homology (biology)Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
- MimicMimicIn evolutionary biology, mimicry is the similarity of one species to another which protects one or both. This similarity can be in appearance, behaviour, sound, scent and even location, with the mimics found in similar places to their models....
ry