1.
Speciation
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Speciation is the evolutionary process by which biological populations evolve to become distinct species. The biologist Orator F. Cook coined the term speciation in 1906 for the splitting of lineages or cladogenesis, Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species. He also identified sexual selection as a mechanism, but found it problematic. There are four modes of speciation in nature, based on the extent to which speciating populations are isolated from one another, allopatric, peripatric, parapatric. Speciation may also be induced artificially, through animal husbandry, agriculture, whether genetic drift is a minor or major contributor to speciation is the subject matter of much ongoing discussion. All forms of speciation have taken place over the course of evolution, however. During allopatric speciation, a population splits into two isolated populations. When the populations come back into contact, they have evolved such that they are isolated and are no longer capable of exchanging genes. Island genetics is the associated with the tendency of small. Examples include insular dwarfism and the changes among certain famous island chains. The Galápagos Islands are particularly famous for their influence on Charles Darwin, though the finches were less important for Darwin, more recent research has shown the birds now known as Darwins finches to be a classic case of adaptive evolutionary radiation. In peripatric speciation, a subform of allopatric speciation, new species are formed in isolated and it is related to the concept of a founder effect, since small populations often undergo bottlenecks. Genetic drift is often proposed to play a significant role in peripatric speciation, parapatric speciation may be associated with differential landscape-dependent selection. Even if there is a gene flow between two populations, strong differential selection may impede assimilation and different species may eventually develop, habitat differences may be more important in the development of reproductive isolation than the isolation time. Ecologists refer to parapatric and peripatric speciation in terms of ecological niches, a niche must be available in order for a new species to be successful. Ring species such as Larus gulls have been claimed to illustrate speciation in progress, the grass Anthoxanthum odoratum may be starting parapatric speciation in areas of mine contamination. Sympatric speciation refers to the formation of two or more descendant species from an ancestral species all occupying the same geographic location. Often-cited examples of sympatric speciation are found in insects that become dependent on different host plants in the same area, however, the existence of sympatric speciation as a mechanism of speciation remains highly debated
2.
Natural selection
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Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in heritable traits of a population over time, Charles Darwin popularised the term natural selection, and compared it with artificial selection. Variation exists within all populations of organisms and this occurs partly because random mutations arise in the genome of an individual organism, and offspring can inherit such mutations. Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits, the environment of a genome includes the molecular biology in the cell, other cells, other individuals, populations, species, as well as the abiotic environment. Individuals with certain variants of the trait may survive and reproduce more than individuals with other, less successful, variants, therefore, factors that affect reproductive success are also important, including sexual selection and fecundity selection. Over time, this process can result in populations that specialise for particular ecological niches, in other words, natural selection is a key process in the evolution of a population. Natural selection can be contrasted with artificial selection, in which humans intentionally choose specific traits, Natural selection is one of the cornerstones of modern biology. The concept of natural selection originally developed in the absence of a theory of heredity, at the time of Darwins writing. The union of traditional Darwinian evolution with subsequent discoveries in classical genetics formed the synthesis of the mid-20th century. The addition of molecular genetics has led to developmental biology. While genotypes can slowly change by random genetic drift, natural selection remains the primary explanation for adaptive evolution, empedocles idea that organisms arose entirely by the incidental workings of causes such as heat and cold was criticised by Aristotle in Book II of Physics. He posited natural teleology in its place, and believed that form was achieved for a purpose, nevertheless, he accepted in his biology that new types of animals, monstrosities, can occur in very rare instances. And in like manner as to the parts in which there appears to exist an adaptation to an end. Yet it is impossible that this should be the true view, for teeth and all other natural things either invariably or normally come about in a given way, but of not one of the results of chance or spontaneity is this true. We do not ascribe to chance or mere coincidence the frequency of rain in winter, but frequent rain in summer we do, nor heat in the dog-days, therefore action for an end is present in things which come to be and are by nature. The struggle for existence was later described by the Islamic writer Al-Jahiz in the 9th century, the classical arguments were reintroduced in the 18th century by Pierre Louis Maupertuis and others, including Darwins grandfather, Erasmus Darwin. Until the early 19th century, the view in Western societies was that differences between individuals of a species were uninteresting departures from their Platonic ideals of created kinds. However, the theory of uniformitarianism in geology promoted the idea that simple and this theory, Lamarckism, was an influence on the Soviet biologist Trofim Lysenkos antagonism to mainstream genetic theory as late as the mid 20th century
3.
Eastern fence lizard
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The eastern fence lizard is a medium-sized species of lizard found along forest edges, rock piles, and rotting logs or stumps in the eastern United States. It is sometimes referred to as the lizard, fence swift, gray lizard. It is also referred to colloquially as the horn-billed lizard, the generic name, Sceloporus, is derived from the Greek skelos/σκελος, meaning leg, and the Latin porus, meaning hole, referring to the enlarged femoral pores found in this genus of lizards. The specific name, undulatus, is Latin for wave, referring to the dark crossbars on the backs of these lizards. Until 2002,10 subspecies of S. undulatus were recognized and these were reclassified as four distinct evolutionary species. The narrowed redefinition of S. undulatus has been suggested to contain two subspecies divided by the Appalachian Mountains. There are isolated populations outside this range in southeastern New York, the eastern fence lizard can grow from 4.0 to 7.5 inches long. It is typically colored in shades of gray or brown, and has keeled scales, a female is usually gray and has a series of dark, wavy lines across her back. The belly is white with black flecks, with pale blue on the throat. The male is brown, and during the summer, has a more greenish-blue and black coloration on the sides of the belly. The young look like the females, but are darker and duller and they closely resemble the western fence lizard, but differ slightly in coloration and live in a different area and habitat. Red fire ants serve a problem towards the eastern fence lizards as they occupy their microhabitats, moreover, according to a study published in 2016, artificial eastern fence lizard nests have shown that predation caused by the fire ants were much more vulnerable. Eastern fence lizards mate in spring, and lay 3 to 16 eggs in spring or early summer. The young hatch in summer and fall, male fence lizards often do push-ups to attract mates and to warn other males encroaching on their territory. Species Sceloporus undulatus at The Reptile Database Pictures and resource information on the eastern fence lizards Care sheet for pet owners of the fence lizard
4.
Homology (biology)
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In biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor, examples include the legs of a centipede, the maxillary palp and labial palp of an insect, and the spinous processes of successive vertebrae in a vertebral column. Sequence homology between protein or DNA sequences is defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either an event or a duplication event. Homology among proteins or DNA is inferred from their sequence similarity, significant similarity is strong evidence that two sequences are related by divergent evolution from a common ancestor. Alignments of multiple sequences are used to discover the homologous regions, the word homology, coined in about 1656, derives from the Greek ὁμόλογος homologos from ὁμός homos same and λόγος logos relation. Homology is the relationship between biological structures or sequences that are derived from a common ancestor, for example, many insects possess two pairs of flying wings. In beetles, the first pair of wings has evolved into a pair of hard wing covers, the same major forearm bones are found in fossils of lobe-finned fish such as Eusthenopteron. The opposite of homologous organs are analogous organs which do similar jobs in two taxa that were not present in their last common ancestor but rather evolved separately. For example, the wings of insects and birds evolved independently in widely separated groups, similarly, the wings of a sycamore maple seed and the wings of a bird are analogous but not homologous, as they develop from quite different structures. A structure can be homologous at one level, but only analogous at another, for example, in the pterosaurs, the wing involves both the forelimb and the hindlimb. Analogy is called homoplasy in cladistics, and convergent or parallel evolution in evolutionary biology, specialised terms are used in taxonomic research. Primary homology is that initially conjectured by a researcher based on similar structure or anatomical connections, secondary homology is implied by parsimony analysis, where a character that only occurs once on a tree is taken to be homologous. As implied in this definition, many cladists consider homology to be synonymous with synapomorphy, homologies provide the fundamental basis for all biological classification, although some may be highly counter-intuitive. The homologies between these have been discovered by comparing genes in evolutionary developmental biology, among insects, the stinger of the female honey bee is a modified ovipositor, homologous with ovipositors in other insects such as the Orthoptera, Hemiptera, and those Hymenoptera without stingers. The three small bones in the ear of mammals including humans, the malleus, incus. The malleus and incus develop in the embryo from structures that form jaw bones in lizards, both lines of evidence show that these bones are homologous, sharing a common ancestor. Among the many homologies in mammal reproductive systems, ovaries and testicles are homologous, in many plants, defensive or storage structures are made by modifications of the development of primary leaves, stems, and roots
5.
Convergent evolution
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Convergent evolution is the independent evolution of similar features in species of different lineages. 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 an example, as flying insects, birds. Functionally similar features that have arisen through convergent evolution are analogous, whereas homologous structures or traits have a common origin, 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 is divergent evolution, where related species evolve different traits, convergent evolution is similar to but different from parallel evolution. Many instances of convergent evolution are known in plants, including the development of C4 photosynthesis, seed dispersal by fleshy fruits adapted to be eaten by animals. In morphology, analogous traits arise when different species live in similar ways and/or a similar environment, when occupying similar ecological niches similar problems can lead to similar solutions. The British anatomist Richard Owen was the first to identify the difference between analogies and homologies. In biochemistry, physical and chemical constraints on mechanisms have caused some active site arrangements such as the 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 the same conditions were encountered again, evolution could take a very different course. In cladistics, a homoplasy is a trait shared by two or more taxa for any other than that they share a common ancestry. Taxa which do share ancestry are part of the same clade, homoplastic traits caused by convergence are therefore, from 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, such a re-emerged trait is called an atavism. From a mathematical standpoint, a gene has a steadily decreasing probability of retaining potential functionality over time. When two species are similar in a character, evolution is defined as parallel if the ancestors were also similar. When the ancestral forms are unspecified or unknown, or the range of traits considered is not clearly specified, 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 as a nucleophile. In order to activate that nucleophile, they orient an acidic, the chemical and physical constraints on enzyme catalysis have caused identical triad arrangements to evolve independently more than 20 times in different enzyme superfamilies
6.
Adaptation
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In biology, an adaptation, also called an adaptive trait, is a trait with a current functional role in the life of an organism that is maintained and evolved by means of natural selection. Adaptation refers to both the current state of being adapted and to the evolutionary process that leads to the adaptation. Adaptations enhance the fitness and survival of individuals, organisms face a succession of environmental challenges as they grow and develop and are equipped with an adaptive plasticity as the phenotype of traits develop in response to the imposed conditions. The developmental norm of reaction for any given trait is essential to the correction of adaptation as it affords a kind of insurance or resilience to varying environments. Adaptation is, first of all, a process, to rather be with the animal, an internal parasite can illustrate the distinction, such a parasite may have a very simple bodily structure, but nevertheless the organism is highly adapted to its specific environment. From this we see that adaptation is not just a matter of visible traits, in such parasites critical adaptations take place in the life cycle, however, as a practical term, adaptation often refers to a product, those features of a species which result from the process. Many aspects of an animal or plant can be correctly called adaptations, by using the term adaptation for the evolutionary process, and adaptive trait for the bodily part or function, one may distinguish the two different senses of the word. Adaptation is one of the two processes that explain the diverse species found in biology, such as the different species of Darwins finches. The other process is speciation, caused by geographical isolation or some other mechanism, a favorite example used today to study the interplay of adaptation and speciation is the evolution of cichlid fish in African lakes, where the question of reproductive isolation is much more complex. Adaptation is not always a simple matter where the ideal phenotype evolves for an external environment. An organism must be viable at all stages of its development and this places constraints on the evolution of development, behavior and structure of organisms. However, it is not clear what relatively small should mean, the origin of eukaryotic symbiosis exemplifies a more dramatic example. All adaptations help organisms survive in their ecological niches, the adaptive traits may be structural, behavioral or physiological. Structural adaptations are features of an organism. Behavioral adaptations are composed of inherited behavior chains and/or the ability to learn, behaviors may be inherited in detail, examples, searching for food, mating, vocalizations. Adaptation, then, affects all aspects of the life of an organism, the following definitions are mainly due to Theodosius Dobzhansky. Adaptation is the process whereby an organism becomes better able to live in its habitat or habitats. Adaptedness is the state of being adapted, the degree to which an organism is able to live, an adaptive trait is an aspect of the developmental pattern of the organism which enables or enhances the probability of that organism surviving and reproducing
7.
Signalling theory
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Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals, both within species and across species. The central question is when organisms with conflicting interests, such as in sexual selection, mathematical models describe how signalling can contribute to an evolutionarily stable strategy. Signals are given in such as mate selection by females. Signals thus evolve because they modify the behaviour of the receiver to benefit the signaller, signals may be honest, conveying information which usefully increases the fitness of the receiver, or dishonest. An individual can cheat by giving a dishonest signal, which might briefly benefit that signaller, amotz Zahavi suggested that cheating could be controlled by the handicap principle, where the best horse in a handicap race is the one carrying the largest handicap weight. According to Zahavis theory, signallers such as male peacocks have tails that are genuinely handicaps, the system is evolutionarily stable as the large showy tails are honest signals. Biologists have attempted to verify the handicap principle, but with inconsistent results, the evolutionary equilibrium depends sensitively on the balance of costs and benefits. When animals choose mates, traits such as signalling are subject to evolutionary pressure, for example, the male gray tree frog, Hyla versicolor, produces a call to attract females. Once a female chooses a mate, this selects for a style of male calling. The signal can be the call itself, the intensity of a call, its style, its repetition rate. Various hypotheses seek to explain why females would select for one call over the other, signallers have sometimes evolved multiple sexual ornaments, and receivers have sometimes evolved multiple trait preferences. In biology, signals are traits, including structures and behaviours, traits or actions that benefit the receiver exclusively are called cues. When an alert bird deliberately gives a call to a stalking predator and the predator gives up the hunt. When a foraging bird inadvertently makes a sound in the leaves that attracts predators and increases the risk of predation. Signalling systems are shaped by mutual interests between signallers and receivers, when the predator gives up, the signaller can get back to other tasks such as feeding. Once the stalking predator is detected, the prey and receiving predator thus have a mutual interest in terminating the hunt. Within species, mutual interests increase with kinship, kinship is central to models of signalling between relatives, for instance when broods of nestling birds beg and compete for food from their parents. The term honesty in communication is controversial because in non-technical usage it implies intent
8.
Anti-predator adaptation
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Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, the first line of defence consists in avoiding detection, through mechanisms such as camouflage, living underground, or nocturnality. Some prey species are capable of fighting back against predators, whether with chemicals, through communal defence, Animals may avoid becoming prey by living out of sight of predators, whether in caves, underground, or by being nocturnal. Nocturnality is an animal behavior characterized by activity during the night and this is a behavioral form of crypsis that can be used by animals to either avoid predation or to enhance prey hunting. Predation risk has long recognized as critical in shaping behavioral decisions. For example, this risk is of prime importance in determining the time of evening emergence in echolocating bats. Although early access during brighter times permits easier foraging, it leads to a higher predation risk from bat hawks. This results in an optimum evening emergence time that is a compromise between the conflicting demands, another nocturnal adaptation can be seen in kangaroo rats, which exhibit moonlight avoidance. These rodents forage in open habitats and reduce their activity outside their nest burrows in response to moonlight. During a full moon, they shift their activity towards areas of dense cover to compensate for the extra brightness. In controlled experiments, artificial moon-like illumination stimulates similar responses in their foraging behavior, camouflage uses any combination of materials, coloration, or illumination for concealment to make the organism hard to detect by sight. It is common in terrestrial and marine animals. Animals such as the horned lizard of North America have evolved to eliminate their shadow. The bodies of these lizards are flattened, and their sides thin towards the edge and this body form, along with the white scales fringed along their sides, allows the lizards to effectively hide their shadows. Additionally, these lizards hide any remaining shadows by pressing their bodies to the ground, many species make use of behavioral strategies to deter predators. Pursuit-deterrent signals are signals used by prey that convince predators not to pursue them. For example, gazelles stot, jumping high with stiff legs and this is thought to signal to predators that they have a high level of fitness and can outrun the predator. As a result, predators may choose to pursue a different prey that is likely to outrun them
9.
Aposematism
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Aposematism was a new term coined by Edward Bagnall Poulton for Alfred Russel Wallaces concept of warning coloration. It describes a family of antipredator adaptations in which a signal is associated with the unprofitability of a prey item to potential predators. Aposematism always involves an advertising signal, the warning signal may take the form of conspicuous animal coloration, sounds, odours or other perceivable characteristics. Aposematic signals are beneficial for both the predator and prey, since both avoid potential harm, aposematism is exploited in Müllerian mimicry, where species with strong defences evolve to resemble one another. By mimicking similarly coloured species, the signal to predators is shared. Warning signals do not necessarily require that a species actually possesses chemical or physical defences to deter predators, the evolution of a warning signal by a mimicking species that resembles a species that possesses strong defences is known as Batesian mimicry. The term aposematism was coined by the English zoologist Edward Bagnall Poulton in his 1890 book The Colours of Animals and he based the term on the Ancient Greek words ἀπό apo away, ση̑μα sēma sign, referring to signs that warn other animals away. The function of aposematism is to prevent attack, by warning potential predators that the animal has defences such as being unpalatable or poisonous. The easily detected warning is a defence mechanism, and the non-visible defences are secondary. Aposematic signals are primarily visual, using bright colours and high-contrast patterns such as stripes, Warning signals are honest indications of noxious prey, because conspicuousness evolves in tandem with noxiousness. Thus, the brighter and more conspicuous the organism, the more toxic it usually is, the most common and effective colours are red, yellow, black and white. These colours provide strong contrast with green foliage, resist changes in shadow and lighting, have strong contrast, are highly chromatic, Warning colouration evolves in response to background, light conditions, and predator vision. Visible signals may be accompanied by odours, sounds or behaviour to provide a signal which is more effectively detected by predators. Unpalatability, broadly understood, can be created in a variety of ways, tiger moths advertise their unpalatability by either producing ultrasonic noises which warn bats to avoid them, or by warning postures which expose brightly coloured body parts, or exposing eyespots. Velvet ants such as Dasymutilla occidentalis both have bright colours and produce audible noises when grabbed, which serve to reinforce the warning, among mammals, predators can be dissuaded when a smaller animal is aggressive and able to defend itself, as for example in honey badgers. Aposematism is widespread in insects, but less so in vertebrates, being confined to a smaller number of reptile, amphibian. Perhaps the most numerous aposematic vertebrates are the dart frogs. Some plants are thought to employ aposematism to warn herbivores of unpalatable chemicals or physical defences such as prickled leaves or thorns, many insects, such as cinnabar moth caterpillars, acquire toxic chemicals from their host plants
10.
Apparent death
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Apparent death, colloquially known as playing dead, feigning death, or playing possum, is a behavior in which an animal takes on the appearance of being dead. This form of deception is an adaptive behavior also known as tonic immobility or thanatosis. Apparent death can be used as a mechanism or as a form of aggressive mimicry. When induced by humans, the state is sometimes known as animal hypnosis. According to Gilman et al. the investigation of animal hypnosis dates back to the year 1646 in a report by Athanasius Kircher, tonic immobility is a behaviour in which some animals become apparently temporarily paralysed and unresponsive to external stimuli. Some sharks can be induced into tonic immobility by inverting them and restraining them by hand, e. g. dogfish sharks, lemon sharks and reef sharks. For tiger sharks, tonic immobility can be induced by placing their hands lightly on the sides of the animals snout in the area surrounding the eyes. During tonic immobility in sharks, the dorsal fins straighten, and this state persists for an average of 15 minutes before recovery and the resumption of active behaviour. Tonic immobility can also be used as a form of anesthesia during experimental manipulations of sharks. Scientists also believe that tonic immobility can be an experience for sharks. By measuring blood chemistry samples when the shark is immobile, it has suggested that tonic immobility can actually put stress on the shark. However, it has also proposed that sharks have a series of compensatory mechanisms that work to increase respiration rates. Goldfish, trout, rudd, tench, brown bullhead, medaka, paradise fish, oscars seem to go into shock when they are stressed, they lie on their side, stop moving their fins, start to breathe more slowly and deeply, and lose colour. A similar behavior has been reported for convict tangs in the field, in 1997, it was reported that around the Farallon Islands off the coast of California, a female orca was seen apparently inducing tonic immobility in a great white shark. The orca held the shark upside down to induce TI and kept the shark still for 15 minutes and this was the first recorded case of predation on a great white shark in the wild by a species other than humans. Another case of orcas apparently inducing TI has been observed with stingrays in New Zealand, in this context, the orcas turn themselves upside down before attacking, trap the stingrays in their mouths then quickly right themselves. This inverts the stingray thereby inducing TI, rendering the fish helpless, tonic immobility can be reliably induced in iguanas by a combination of inversion, restraint and moderate pressure. During TI, there are changes in respiration including a decline in respiration rate, the rhythm becomes sporadic
Gulick, John T. (September 1888). "Divergent Evolution through Cumulative Segregation". Journal of the Linnean Society of London, Zoology. 20 (120): 189–274. doi:10.1111/j.1096-3642.1888.tb01445.x. Retrieved 26 September 2011. (subscription required)
