Captive breeding is the process of maintaining plants or animals in controlled environments, such as wildlife reserves, botanic gardens, other conservation facilities. It is sometimes employed to help species that are being threatened by human activities such as habitat loss, over hunting or fishing, predation and parasitism. In some cases a captive breeding program can save a species from extinction, but for success, breeders must consider many factors—including genetic, ecological and ethical issues. Most successful attempts involve the coordination of many institutions. Captive breeding techniques began with the first human domestication of animals such as goats, plants like wheat, at least 10,000 years ago; these practices were expanded with the rise of the first zoos, which started as royal menageries in Egypt and its popularity, which led to the increase in zoos worldwide. The first actual captive breeding programs were only started in the 1960s; these programs, such as the Arabian Oryx breeding program from The Phoenix Zoo in 1962, were aimed at the reintroduction of these species into the wild.
These programs expanded under The Endangered Species Act of 1973 of the Nixon Administration, which focused on protecting endangered species and their habitats to preserve biodiversity. Since research and conservation centers have been housed in zoos, such as the Institute for Conservation Research at the San Diego Zoo founded in 1975 and expanded in 2009, which have contributed to the successful conservation efforts of species such as the Hawaiian Crow; the breeding of species of conservation concern is coordinated by cooperative breeding programs containing international studbooks and coordinators, who evaluate the roles of individual animals and institutions from a global or regional perspective. These studbooks contain information on birth date, gender and lineage, which helps determine survival and reproduction rates, number of founders of the population, inbreeding coefficients. A species coordinator reviews the information in studbooks and determines a breeding strategy that would produce most advantageous offspring.
If two compatible animals are found at different zoos, the animals may be transported for mating, but this is stressful, which could in turn make mating less likely. However, this is still a popular breeding method among European zoological organizations. Artificial fertilization is another option, but male animals can experience stress during semen collection, the same goes for females during the artificial insemination procedure. Furthermore, this approach yields lower-quality semen, because shipping requires extending the life of the sperm for the transit time. There are regional programmes for the conservation of endangered species: Americas: Species Survival Plan SSP Europe: European Endangered Species Programme EEP Australasia: Australasian Species Management Program ASMP Africa: African Preservation Program APP Japan: Conservation activities of Japanese Association of Zoos and Aquariums JAZA South Asia: Conservation activities of South Asian Zoo Association for Regional Cooperation SAZARC South East Asia: Conservation activities of South East Asian Zoos Association SEAZA The objective of many captive populations is to hold similar levels of genetic diversity to what is found in wild populations.
As captive populations are small and maintained in artificial environments, genetics factors such as adaptation and loss of diversity can be a major concern. Adaptive differences between plant and animal populations arise due to variations in environmental pressures. In the case of captive breeding prior to reintroduction into the wild, it's possible for species to evolve to adapt to the captive environment, rather than their natural environment. Reintroducing a plant or animal to an environment dissimilar to the one they were from can cause fixation of traits that may not be suited for that environment leaving the individual disadvantaged. Selection intensity, initial genetic diversity, effective population size can impact how much the species adapts to its captive environment. Modeling works indicate that the duration of the programs is an important determinant of reintroduction success. Success is maximized for intermediate project duration allowing the release of a sufficient number of individuals, while minimizing the number of generations undergoing relaxed selection in captivity.
Can be minimized by reducing the number of generations in captivity, minimizing selection for captive adaptations by creating environment similar to natural environment and maximizing the number of immigrants from wild populations. One consequence of small captive population size is the increased impact of genetic drift, where genes have the potential to fix or disappear by chance, thereby reducing genetic diversity. Other factors that can impact genetic diversity in a captive population are bottlenecks and initial population size. Bottlenecks, such as rapid decline in the population or a small initial population impacts genetic diversity. Loss can be minimized by establishing a population with a large enough number of founders to genetically represent the wild population, maximize population size, maximize ratio of effective population size to actual population size, minimize the number of generations in captivity. Inbreeding is when organisms mate with related individuals
In evolutionary genetics, Muller's ratchet is a process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner. Muller proposed this mechanism as one reason why sexual reproduction may be favored over asexual reproduction; the negative effect of accumulating irreversible deleterious mutations may not be prevalent in organisms, while they reproduce asexually undergo other forms of recombination. This effect has been observed in those regions of the genomes of sexual organisms that do not undergo recombination. Although Muller discussed the advantages of sexual reproduction in his 1932 talk, it does not contain the word "ratchet". Muller first introduced the term "ratchet" in his 1964 paper, the phrase "Muller's ratchet" was coined by Joe Felsenstein in his 1974 paper, "The Evolutionary Advantage of Recombination". Asexual reproduction compels genomes to be inherited as indivisible blocks so that once the least mutated genomes in an asexual population begin to carry at least one deleterious mutation, no genomes with fewer such mutations can be expected to be found in future generations.
This results in an eventual accumulation of mutations known as genetic load. In theory, the genetic load carried by asexual populations becomes so great that the population goes extinct. In sexual populations, the process of genetic recombination allows the genomes of the offspring to be different from the genomes of the parents. In particular, progeny genomes with fewer mutations can be generated from more mutated parental genomes by putting together mutation-free portions of parental chromosomes. Among protists and prokaryotes, a plethora of asexual organisms exists. More and more are being shown to exchange genetic information through a variety of mechanisms. In contrast, the genomes of mitochondria and chloroplasts do not recombine and would undergo Muller's ratchet were they not as small as they are. Indeed, the probability that the least mutated genomes in an asexual population end up carrying at least one mutation depends on the genomic mutation rate and this increases more or less linearly with the size of the genome.
However, reductions in genome size in parasites and symbionts, can be caused by direct selection to get rid of genes that have become unnecessary. Therefore, a smaller genome is not a sure indication of the action of Muller's ratchet. In sexually reproducing organisms, nonrecombining chromosomes or chromosomal regions such as the mammalian Y chromosome should be subject to the effects of Muller's ratchet; such nonrecombining sequences tend to evolve quickly. However, this fast evolution might be due to these sequences' inability to repair DNA damage via template-assisted repair, equivalent to an increase in the mutation rate for these sequences. Ascribing cases of genome shrinkage or fast evolution to Muller's ratchet alone is not easy; because Muller's ratchet relies on genetic drift, it turns faster in smaller populations and is thought to set limits to the maximum size of asexual genomes and to the long-term evolutionary continuity of asexual lineages. However, some asexual lineages are thought to be quite ancient.
However, rotifers were found to possess a substantial number of foreign genes from possible horizontal gene transfer events. It has been argued. Early RNA replicators capable of recombination may have been the ancestral sexual source from which asexual lineages could periodically emerge. Recombination in the early sexual lineages may have provided a means for coping with genome damage. Muller's ratchet under such ancient conditions would have impeded the evolutionary persistence of the asexual lineages that were unable to undergo recombination. Evolution of sexual reproduction Genetic hitchhiking Mutational meltdown Hill-Robertson effect
Fiordland is a geographic region of New Zealand in the south-western corner of the South Island, comprising the western-most third of Southland. Most of Fiordland is dominated by the steep sides of the snow-capped Southern Alps, deep lakes, its steep, glacier-carved and now ocean-flooded western valleys; the name "Fiordland" comes from a variant spelling of the Scandinavian word for this type of steep valley, "fjord". The area of Fiordland is dominated by, roughly coterminous with, Fiordland National Park, New Zealand's largest National Park. Due to the steep terrain and high amount of rainfall supporting dense vegetation, the interior of the Fiordland region is inaccessible; as a result, Fiordland was never subjected to notable logging operations, attempts at whaling, seal hunting, mining were on a small scale and shortlived also because of the challenging weather. Today, Fiordland contains by far the greatest extent of unmodified vegetation in New Zealand and significant populations of endemic plants and threatened animals, in some cases the only remaining wild populations.
Fiordland features a number of fiords, which in this area are named sounds though geologically they are not. Of the twelve major fiords on Fiordland's west coast, Milford Sound is the most famous and the only one accessible by road. Doubtful Sound, much larger, is a tourist destination, but is less accessible as it requires a boat trip over Lake Manapouri and bus transfer over Wilmot Pass. Situated within Fiordland are Browne Falls and Sutherland Falls, which rank among the tallest waterfalls in the world, New Zealand's three deepest lakes, Lake Hauroko, Lake Manapouri, Lake Te Anau. Several other large lakes lie nearby, Fiordland and the surrounding parts of Southland and Otago Regions are referred to as the Southern Lakes. Only a handful of Fiordland's lakes are accessible by road - Lake Poteriteri is the largest lake in New Zealand with no road access. Many of the region's lakes are not accessible via tramping tracks; this part of New Zealand to the west of the mountain divide of the Southern Alps, has a wet climate with annual average of 200 rainy days and annual rainfall varying from 1,200 millimetres in Te Anau to 8,000 millimetres in Milford Sound.
The prevailing westerly winds blow moist air from the Tasman Sea onto the mountains, resulting in high amounts of precipitation as the air rises and cools down. Fiordland has never had any significant permanent population; the Maori people, whose livelihood was present in this region, arrived temporarily, for hunting, fishing and to collect the precious stone pounamu from Anita Bay and the mouth of Milford Sound. In Maori legend, demi-god Tu-te-raki-whanoa carved the fiords from rock using his adze, perfecting his technique as he progressed from south to north, with the last fiord, Piopiotahi being his greatest achievement. In 1773, Captain James Cook and his crew were the first Europeans to visit Fiordland, anchored in Dusky Sound for five weeks; the expedition's maps and descriptions of the area attracted whalers and seal hunters, but it was not until the mid-19th century that surveyors and prospectors began exploring Fiordland's interior. Between 1897 and 1908, two attempts at establishing a mining operation in the remote area of Preservation Island failed, by 1914, the isolated small settlement of Cromartie had been abandoned.
The area was administered as Fiord County from 1876 until it was absorbed into neighbouring Wallace County in 1981. Since 1989 it has been part of Southland District, the wider Southland Region. There are varying definitions for the boundary of the Fiordland region; the eastern boundary of Fiordland according to Statistics New Zealand stretches from Sand Hill Point on the western end of Te Waewae Bay more or less straight north, cutting through Lake Hauroko, Lake Monowai, Lake Manapouri, Lake Te Anau's South Fiord, before veering northwest and ending with the southern side of George Sound. By that definition, the Fiordland region is entirely within the Fiordland National Park, except for small pockets near the two southernmost lakes, but the area does not include the three northernmost fiords Milford Sound, Southerland Sound, Bligh Sound; the much more widespread definition of "Fiordland" has an eastern boundary that follows that of the Fiordland National Park for all but the northernmost end.
This area contains all fiords as well as the Hollyford Valley and includes the area around Big Bay, which lies to the north outside of the Fiordland National Park, but still belongs to the Southland Region. This definition of the Fiordland region is used by tourism organisations and the Department of Conservation; the towns of Te Anau and Manapouri are also referred to as being within the Fiordland region though they are outside of the boundary of the national park. In geographical terms, the Fiordland region contains the huge mountainous regions west of the line from Te Waewae Bay to Monowai to Te Anau, includes the valleys of the Eglinton River and Hollyford River; the area is identical to that of the Fiordland National Park, is marked by U-shaped valleys and fiords along the coast and steep mountains with foundations of hard rocks like gneiss, schist and diorite, with the softer rock having been carved out by multiple glaciations. Fiordland contains New Zealand's oldest known plutonic rocks and is dominated by the southernmost extent of the Southern Alps as the peaks reduce in height from north to south.
The tallest mountain in the Fiordland region is Mount Tutoko at 2,723 metres, one of several peaks over 2,000 meters in the Darren Mountains. Southeast of t
Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are related genetically. By analogy, the term is used in human reproduction, but more refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity. Inbreeding results in homozygosity, which can increase the chances of offspring being affected by deleterious or recessive traits; this leads to at least temporarily decreased biological fitness of a population, its ability to survive and reproduce. An individual who inherits such deleterious traits is colloquially referred to as inbred; the avoidance of expression of such deleterious recessive alleles caused by inbreeding, via inbreeding avoidance mechanisms, is the main selective reason for outcrossing. Crossbreeding between populations often has positive effects on fitness-related traits, but sometimes leads to negative effects known as outbreeding depression.
However increased homozygosity increases probability of fixing beneficial alleles and slightly decreases probability of fixing deleterious alleles in population. Inbreeding can result in purging of deleterious alleles from a population through purifying selection. Inbreeding is a technique used in selective breeding. For example, in livestock breeding, breeders may use inbreeding when trying to establish a new and desirable trait in the stock and for producing distinct families within a breed, but will need to watch for undesirable characteristics in offspring, which can be eliminated through further selective breeding or culling. Inbreeding helps to ascertain the type of gene action affecting a trait. Inbreeding is used to reveal deleterious recessive alleles, which can be eliminated through assortative breeding or through culling. In plant breeding, inbred lines are used as stocks for the creation of hybrid lines to make use of the effects of heterosis. Inbreeding in plants occurs in the form of self-pollination.
Inbreeding can influence gene expression which can prevent inbreeding depression. Offspring of biologically related persons are subject to the possible effects of inbreeding, such as congenital birth defects; the chances of such disorders are increased when the biological parents are more related. This is because such pairings have a 25% probability of producing homozygous zygotes, resulting in offspring with two recessive alleles, which can produce disorders when these alleles are deleterious; because most recessive alleles are rare in populations, it is unlikely that two unrelated marriage partners will both be carriers of the same deleterious allele. It should be noted that for each homozygous recessive individual formed there is an equal chance of producing a homozygous dominant individual — one devoid of the harmful allele. Contrary to common belief, inbreeding does not in itself alter allele frequencies, but rather increases the relative proportion of homozygotes to heterozygotes. In the short term, incestuous reproduction is expected to increase the number of spontaneous abortions of zygotes, perinatal deaths, postnatal offspring with birth defects.
The advantages of inbreeding may be the result of a tendency to preserve the structures of alleles interacting at different loci that have been adapted together by a common selective history. Malformations or harmful traits can stay within a population due to a high homozygosity rate, this will cause a population to become fixed for certain traits, like having too many bones in an area, like the vertebral column of wolves on Isle Royale or having cranial abnormalities, such as in Northern elephant seals, where their cranial bone length in the lower mandibular tooth row has changed. Having a high homozygosity rate is problematic for a population because it will unmask recessive deleterious alleles generated by mutations, reduce heterozygote advantage, it is detrimental to the survival of small, endangered animal populations; when deleterious recessive alleles are unmasked due to the increased homozygosity generated by inbreeding, this can cause inbreeding depression. There may be other deleterious effects besides those caused by recessive diseases.
Thus, similar immune systems may be more vulnerable to infectious diseases. Inbreeding history of the population should be considered when discussing the variation in the severity of inbreeding depression between and within species. With persistent inbreeding, there is evidence that shows that inbreeding depression becomes less severe; this is associated with the unmasking and elimination of deleterious recessive alleles. However, inbreeding depression is not a temporary phenomenon because this elimination of deleterious recessive alleles will never be complete. Eliminating deleterious mutations through inbreeding under moderate selection is not as effective. Fixation of alleles most occurs through Muller's ratchet, when an asexual population's genome accumulates deleterious mutations that are irreversible. Despite all its disadvantages, inbreeding can have a variety of advantages, such as reducing the recombination load, allowing the expression of recessive advantageous phenotypes, it has been proposed th
Genetic variation describes the difference in DNA among individuals. There are multiple sources including Mutation and Genetic recombination. Genetic variation can be identified at a many levels, it is possible to identify genetic variation from observations of phenotypic variation in either quantitative traits or discrete traits. Genetic variation can be identified by examining variation at the level of enzymes using the process of protein electrophoresis. Polymorphic genes have more than one allele at each locus. Half of the genes that code for enzymes in insects and plants may be polymorphic, whereas polymorphisms are less common among vertebrates. Genetic variation is caused by variation in the order of bases in the nucleotides in genes. New technology now allows scientists to directly sequence DNA which has identified more genetic variation than was detected by protein electrophoresis. Examination of DNA has shown genetic variation in both coding regions and in the non-coding intron region of genes.
Genetic variation will result in phenotypic variation if variation in the order of nucleotides in the DNA sequence results in a difference in the order of amino acids in proteins coded by that DNA sequence, if the resultant differences in amino acid sequence influence the shape, thus the function of the enzyme. Geographic variation means genetic differences in populations from different locations; this is caused by genetic drift. Genetic variation within a population is measured as the percentage of gene loci that are polymorphic or the percentage of gene loci in individuals that are heterozygous. Random mutations are the ultimate source of genetic variation. Mutations are to be rare and most mutations are neutral or deleterious, but in some instances, the new alleles can be favored by natural selection. Polyploidy is an example of chromosomal mutation. Polyploidy is a condition. Crossing over and random segregation during meiosis can result in the production of new alleles or new combinations of alleles.
Furthermore, random fertilization contributes to variation. Variation and recombination can be facilitated by transposable genetic elements, endogenous retroviruses, LINEs, SINEs, etc. For a given genome of a multicellular organism, genetic variation may be acquired in somatic cells or inherited through the germline. Genetic variation can be divided into different forms according to the size and type of genomic variation underpinning genetic change. Small-scale sequence variation indels. Large-scale structural variation can be chromosomal rearrangement. Genetic variation and recombination by transposable elements and endogenous retroviruses sometimes is supplemented by a variety of persistent viruses and their defectives which generate genetic novelty in host genomes. Numerical variation in whole chromosomes or genomes can be either aneuploidy. A variety of factors maintain genetic variation in populations. Harmful recessive alleles can be hidden from selection in the heterozygous individuals in populations of diploid organisms.
Natural selection can maintain genetic variation in balanced polymorphisms. Balanced polymorphisms may occur when heterozygotes are favored or when selection is frequency dependent. Genetic diversity Genetic variability Human genetic variation Mayr E.: Populations and evolution – An abridgment of Animal species and evolution. The Belknap Press of Harvard University Press, Cambridge and London, England, ISBN 0-674-69013-3. Dobzhansky T.: Genetics of the evolutionary process. Columbia, New York, ISBN 0-231-02837-7. McGinley, Mark. 2008. "Genetic variation." In: Encyclopedia of Earth. Washington, D. C.: National Council for Science and the Environment. "Genetic Variation" in Griffiths, A. J. F. Modern Genetic Analysis, Vol 2. P. 7 "How is Genetic Variation Maintained in Populations" in Sadava, D. et al. Life: The Science of Biology, p. 456 Nevo, E.. "Genetic variation in nature". Scholarpedia, 6:8821. Doi:10.4249/scholarpedia.8821 Hedrick P.: Genetics of populations. Jones & Bartlett Learning, ISBN 978-0-7637-5737-3.
Albers P. K. and McVean G.: Dating genomic variants and shared ancestry in population-scale sequencing data. BioRxiv: 416610. Doi:10.1101/416610. Rieger R. Michaelis A. Green M. M.: Glossary of genetics and cytogenetics: Classical and molecular. Springer-Verlag, Heidelberg - New York, ISBN 3-540-07668-9. Griffiths, A. J. F.. An Introduction to genetic analysis. W. H. Freeman, San Francisco, ISBN 0-7167-3520-2. Cavalli-Sforza L. L. Bodmer W. F.: The genetics of human populations. Dover, New York, ISBN 0-486-40693-8. Genetic variation[[pl:Zmienność genetyczna
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages. Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species, he identified sexual selection as a mechanism, but found it problematic. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are isolated from one another: allopatric, peripatric and sympatric. Speciation may be induced artificially, through animal husbandry, agriculture, or laboratory experiments. Whether genetic drift is a minor or major contributor to speciation is the subject matter of much ongoing discussion. Rapid sympatric speciation can take place through polyploidy, such as by doubling of chromosome number. New species can be created through hybridisation followed, if the hybrid is favoured by natural selection, by reproductive isolation.
In addressing the question of the origin of species, there are two key issues: what are the evolutionary mechanisms of speciation, what accounts for the separateness and individuality of species in the biota? Since Charles Darwin's time, efforts to understand the nature of species have focused on the first aspect, it is now agreed that the critical factor behind the origin of new species is reproductive isolation. Next we focus on the second aspect of the origin of species. In On the Origin of Species, Darwin interpreted biological evolution in terms of natural selection, but was perplexed by the clustering of organisms into species. Chapter 6 of Darwin's book is entitled "Difficulties of the Theory." In discussing these "difficulties" he noted "Firstly, why, if species have descended from other species by insensibly fine gradations, do we not everywhere see innumerable transitional forms? Why is not all nature in confusion instead of the species being, as we see them, well defined?" This dilemma can be referred to as the rarity of transitional varieties in habitat space.
Another dilemma, related to the first one, is the absence or rarity of transitional varieties in time. Darwin pointed out that by the theory of natural selection "innumerable transitional forms must have existed," and wondered "why do we not find them embedded in countless numbers in the crust of the earth." That defined species do exist in nature in both space and time implies that some fundamental feature of natural selection operates to generate and maintain species. It has been argued that the resolution of Darwin's first dilemma lies in the fact that out-crossing sexual reproduction has an intrinsic cost of rarity; the cost of rarity arises. If, on a resource gradient, a large number of separate species evolve, each exquisitely adapted to a narrow band on that gradient, each species will, of necessity, consist of few members. Finding a mate under these circumstances may present difficulties when many of the individuals in the neighborhood belong to other species. Under these circumstances, if any species’ population size happens, by chance, to increase, this will make it easier for its members to find sexual partners.
The members of the neighboring species, whose population sizes have decreased, experience greater difficulty in finding mates, therefore form pairs less than the larger species. This has a snowball effect, with large species growing at the expense of the smaller, rarer species driving them to extinction. Only a few species remain, each distinctly different from the other; the cost of rarity not only involves the costs of failure to find a mate, but indirect costs such as the cost of communication in seeking out a partner at low population densities. Rarity brings with it other costs. Rare and unusual features are seldom advantageous. In most instances, they indicate a mutation, certain to be deleterious, it therefore behooves sexual creatures to avoid mates sporting unusual features. Sexual populations therefore shed rare or peripheral phenotypic features, thus canalizing the entire external appearance, as illustrated in the accompanying illustration of the African pygmy kingfisher, Ispidina picta.
This uniformity of all the adult members of a sexual species has stimulated the proliferation of field guides on birds, reptiles and many other taxa, in which a species can be described with a single illustration. Once a population has become as homogeneous in appearance as is typical of most species, its members will avoid mating with members of other populations that look different from themselves. Thus, the avoidance of mates displaying rare and unusual phenotypic features leads to reproductive isolation, one of the hallmarks of speciation. In the contrasting case of organisms that reproduce asexually, there is no cost of rarity. Thus, asexual organisms frequently show the continuous variation in form that Darwin expected evolution to produce, making their classification into "species" difficult. All forms of natural speciation have taken place over the course of evolution.
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary. Genetic diversity serves as a way for populations to adapt to changing environments. With more variation, it is more that some individuals in a population will possess variations of alleles that are suited for the environment; those individuals are more to survive to produce offspring bearing that allele. The population will continue for more generations because of the success of these individuals; the academic field of population genetics includes several hypotheses and theories regarding genetic diversity. The neutral theory of evolution proposes that diversity is the result of the accumulation of neutral substitutions. Diversifying selection is the hypothesis that two subpopulations of a species live in different environments that select for different alleles at a particular locus; this may occur, for instance, if a species has a large range relative to the mobility of individuals within it.
Frequency-dependent selection is the hypothesis that as alleles become more common, they become more vulnerable. This occurs in host–pathogen interactions, where a high frequency of a defensive allele among the host means that it is more that a pathogen will spread if it is able to overcome that allele. A study conducted by the National Science Foundation in 2007 found that genetic diversity and biodiversity are dependent upon each other — i.e. that diversity within a species is necessary to maintain diversity among species, vice versa. According to the lead researcher in the study, Dr. Richard Lankau, "If any one type is removed from the system, the cycle can break down, the community becomes dominated by a single species." Genotypic and phenotypic diversity have been found in all species at the protein, DNA, organismal levels. The interdependence between genetic and species diversity is delicate. Changes in species diversity lead to changes in the environment, leading to adaptation of the remaining species.
Changes in genetic diversity, such as in loss of species, leads to a loss of biological diversity. Loss of genetic diversity in domestic animal populations has been studied and attributed to the extension of markets and economic globalization. Variation in the populations gene pool allows natural selection to act upon traits that allow the population to adapt to changing environments. Selection for or against a trait can occur with changing environment – resulting in an increase in genetic diversity or a decrease in genetic diversity. Hence, genetic diversity plays an important role in the adaptability of a species; the capability of the population to adapt to the changing environment will depend on the presence of the necessary genetic diversity The more genetic diversity a population has, the more likelihood the population will be able to adapt and survive. Conversely, the vulnerability of a population to changes, such as climate change or novel diseases will increase with reduction in genetic diversity.
For example, the inability of koalas to adapt to fight Chlamydia and the koala retrovirus has been linked to the koala’s low genetic diversity. This low genetic diversity has geneticists concerned for the koalas ability to adapt to climate change and human-induced environmental changes in the future. Large populations are more to maintain genetic material and thus have higher genetic diversity. Small populations are more to experience the loss of diversity over time by random chance, called genetic drift; when an allele drifts to fixation, the other allele at the same locus is lost, resulting in a loss in genetic diversity. In small population sizes, inbreeding, or mating between individuals with similar genetic makeup, is more to occur, thus perpetuating more common alleles to the point of fixation, thus decreasing genetic diversity. Concerns about genetic diversity are therefore important with large mammals due to their small population size and high levels of human-caused population effects.
A genetic bottleneck can occur when a population goes through a period of low number of individuals, resulting in a rapid decrease in genetic diversity. With an increase in population size, the genetic diversity continues to be low if the entire species began with a small population, since beneficial mutations are rare, the gene pool is limited by the small starting population; this is an important consideration in the area of conservation genetics, when working toward a rescued population or species, genetically-healthy. Random mutations generate genetic variation. A mutation will increase genetic diversity in the short term, as a new gene is introduced to the gene pool. However, the persistence of this gene is dependent of selection. Most new mutations either have a neutral or negative effect on fitness, while some have a positive effect. A beneficial mutation is more to persist and thus have a long-term positive effect on genetic diversity. Mutation rates differ across the genome, larger populations have greater mutation rates.
In smaller populations a mutation is less to persist because it is more to be eliminated by drift. Gene flow by migration, is the movement of genetic material. Gene flow can introduce novel alleles to a population; these alleles