Genetic isolate

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A genetic isolate is a population of organisms that has little to no genetic mixing with other organisms of the same species due to geographic isolation or other factors that prevent reproduction. Genetic isolates form new species through an evolutionary process known as speciation. All modern species diversity is a product of genetic isolates and evolution.[ citation needed ]

Contents

The current distribution of genetic differences and isolation within and among populations is also influenced by genetic processes. The resulting genetic diversity within a species' distribution range is frequently unequally distributed, and significant disparities can occur when population dispersion and isolation are critical for species survival. [1]

The interrelationship of genetic drift, gene flow, and natural selection determines the level and dispersion of genetic differences between populations and among species assemblages. [2] Geographic and natural elements may likewise add to these cycles and lead to examples of hereditary variety, such as genetic differences that cause genetic isolation. [3] Genetic variations are often unequally distributed over a species' geographic distribution, with differences between populations at the geographic center and the range's extremities. [4]

Significant gene flow occurs in core populations, resulting in genetic uniformity. In contrast, low gene flow, severe genetic drift, and diverse selection conditions occur in range periphery populations, enhancing genetic isolation and heterogeneity among people. [5] Genetic differentiation resulting from genetic isolation occurs as significant alterations in genetic variations, such as fluctuations in allelic frequencies, accumulate over time.[ citation needed ]

Significant genetic diversity can be detected toward the limits of a species range, where population fragmentation and isolation are more likely to affect genetic processes. Regional splitting is produced by a variety of factors, including environmental processes that regularly change a species' indigenous distribution. [6] For example, human-caused environmental changes such as deforestation and land degradation can result in rapid changes in a species' distribution, leading to population decrease, segmentation, and regional isolation. [7]

Definition

Genetic isolation is a population of organisms that has little to no genetic mixing with other organisms of the same species. Such isolation may lead to speciation, but this is not guaranteed. Genetic isolates may form new species in several ways:

Human-driven genetic isolates include restricted breeding of dogs or a community living secluded away from others, such as Tristan da Cunha or the Pitcairn Islands. More significant and less secluded human genetic isolates include groups of people like the Sardinians or the Finns.[ citation needed ]

Genetic isolation, in combination with diminishing habitat quality and a limited population density, is likely to result in a population's collapse and ultimate extinction. [8] Random mutation rate, drift, high rates of inbreeding, restricted gene flow, and regional extinction have all been shown to increase with isolation. Varying climatic conditions, such as particular geographic climatic changes, can cause pressures that drastically change a species' genetic composition, yielding genetic differences through different selection processes [9] as well as leading to increased genetic isolation within populations. [10]

Environmental heterogeneity has historically been identified as a vital source of genetic variations and distinctions due to isolation, and several studies have found correlations between neutral genetic differences, ecological heterogeneity, and genetic isolation. The genetic isolation and different associations in regional heterogeneity could be cited as evidence of diversifying selection working across entire genomes, encompassing manifestly neutral genes. They can be used to predict the long-term effects of environmental factors on genetic diversity and isolation. [11]

Genetic isolation by environment or distance

Strong gene flow across populations can help local adaptation by bringing new genetic variations into population groups, but it can also impede adaptation by overwhelming locally beneficial genes. Population size, genetic diversity, and the environment can all affect the outcome. Isolation by distance (IBD), wherein population growth rates and immigration numbers are inversely proportional to population distance, may correlate gene flow patterns with geographic distance. Gene flow may also follow patterns of isolation by habitat, with higher rates of gene flow among an increasingly common form. Moreover, gene flow may be greatest across dissimilar areas. [12] When the population size is limited, and individuals are subjected to strong selection, gene flow can boost population numbers, even if the phenotypes that arise are generally mis-adapted. This can lead to increases in genetic differences that lead to isolation, allowing new adaptations to take hold. [13]

The Influence of dispersal and diet on patterns of genetic isolation

Gene flow across populations is considered key in evolving local adaptations and speciation. Assessing genetic separation by distance is necessary to determine the impacts of dispersal ability and food breadth on genetic population structure. Strong dispersers have a mild IBD (isolation by distance) because of the homogenizing effects of gene flow, whereas stationary species have limited gene flow, which permits nearly all populations to isolate. Genetic uniformity is achieved at small geographical scales in intermediate dispersers, whereas limited dispersal increases genetic variability across vast distances.[ citation needed ] IBD is also thought to rise with decreasing food breadth, putting the theory that specialization promotes speciation by affecting population genetic subdivision to the test. In studies of IBD, the number of people is more essential than the number of multiple alleles per locus. [14]

Genetic isolation in sympatric species

Adaptation to diverse positions and climatic conditions could be a significant source of genetic differences and population isolation. Pleiotropic-induced sexual selection between individuals of these genetically diverse populations can be caused by biological features selected for in each habitat. Such conditions could make sympatric speciation easier. For example, successful host transitions in phytophagous insects provide compelling evidence for ecological diversification in sympatric speciation. [15]

Current patterns of genetic isolation on islands

The genetic structure of species on an isolated island is influenced by a range of environmental variables, with some species being influenced by single contours and others being influenced by many species. Sister species and congenerics have various contributing elements to isolation within species. [16] Individuals from several vegetation types on an island are often genetically connected, demonstrating that ecological and climatic factors have a role in determining gene flow configurations on a small island.[ citation needed ]

Genetic isolation in fragmented populations

The link between statistical genetic differences and population size has received scant scientific attention, even though small populations have less genetic variation at marker loci. Researchers have shown that in smaller fragmented meta-populations, both neutral and quantifiable genetic variation is reduced, and both drift and selection change is amplified. [17]

Genetic isolation and the burden of genetic diversity

Species with enormous ecological amplitudes, on the whole, have a lot of genetic diversity. On the other hand, more specialized species with small ecological amplitude and frequency have minimal genetic diversity. Inbreeding depressions may pose the greatest threat to species with moderate habitat demands and substantial genetic diversity. [18]

Advantages

In most situations, highly specialized species are constrained to a small portion of the accessible environment. [19] This ecological specialization, and consequently geographical constraint of indigenous populations, is frequently accompanied by a reduction in gene flow, resulting in small population sizes and genetic differentiation. As a result, due to genetic isolation, such species can only survive if they are suited to minimal genetic isolation. [20] [21]

In the search for lethal genes, genetic isolates with a background of a small founding population, long-term isolation, and population bottlenecks are invaluable resources. Specific rare, monogenic disorders get enhanced, and families with numerous sick members become common enough to be employed in locus-identifying linkage analyses. Besides that, most cases are caused by the same mutation, and diseased alleles expose the linkage of disequilibrium with molecular markers over strong genetic distances, making disease locus recognition easier in small study samples with few individuals affected using a similarity search for a shared genotype. The presence of disequilibrium linkage in disease alleles enhances linkage analysis and aids in determining the precise position of the disease locus on the genome sequence. [22]

Disadvantages

Many species fall somewhere between generalist and specialist on the generalist-specialist range. Such species generally exhibit moderate environmental specialization, being neither pure generalists nor pure specialists, resulting in fluid changes that must be evaluated when categorizing species. Despite their considerable habitat specialization, environmentally transitional species generally do not exhibit the low genetic diversity seen in pure specialists, but instead exhibit species-specific genetic differences on the scale with generalists. Conversely, these taxa are categorized as far more endangered than their degree of specialization would suggest. This scenario can be harmful in the progression of population decline and may be one of the promoters of extinction in this instance, owing to the genomic instability of populations and unpredictable aggregation of detrimental genes. [23]

See also

Related Research Articles

<span class="mw-page-title-main">Evolution</span> Change in the heritable characteristics of biological populations

Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation.

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 On the Origin of Species. He also identified sexual selection as a likely mechanism, but found it problematic.

<span class="mw-page-title-main">Gene flow</span> Transfer of genetic variation from one population to another

In population genetics, gene flow is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent allele frequencies and therefore can be considered a single effective population. It has been shown that it takes only "one migrant per generation" to prevent populations from diverging due to drift. Populations can diverge due to selection even when they are exchanging alleles, if the selection pressure is strong enough. Gene flow is an important mechanism for transferring genetic diversity among populations. Migrants change the distribution of genetic diversity among populations, by modifying allele frequencies. High rates of gene flow can reduce the genetic differentiation between the two groups, increasing homogeneity. For this reason, gene flow has been thought to constrain speciation and prevent range expansion by combining the gene pools of the groups, thus preventing the development of differences in genetic variation that would have led to differentiation and adaptation. In some cases dispersal resulting in gene flow may also result in the addition of novel genetic variants under positive selection to the gene pool of a species or population

Allopatric speciation – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow.

<span class="mw-page-title-main">Sympatric speciation</span> Evolution of a new species from an ancestor in the same location

In evolutionary biology, sympatric speciation is the evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region. In evolutionary biology and biogeography, sympatric and sympatry are terms referring to organisms whose ranges overlap so that they occur together at least in some places. If these organisms are closely related, such a distribution may be the result of sympatric speciation. Etymologically, sympatry is derived from Greek συν (sun-) 'together', and πατρίς (patrís) 'fatherland'. The term was coined by Edward Bagnall Poulton in 1904, who explains the derivation.

<span class="mw-page-title-main">Biological dispersal</span> Movement of individuals from their birth site to a breeding site

Biological dispersal refers to both the movement of individuals from their birth site to their breeding site, as well as the movement from one breeding site to another . Dispersal is also used to describe the movement of propagules such as seeds and spores. Technically, dispersal is defined as any movement that has the potential to lead to gene flow. The act of dispersal involves three phases: departure, transfer, and settlement. There are different fitness costs and benefits associated with each of these phases. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution. Understanding dispersal and the consequences, both for evolutionary strategies at a species level and for processes at an ecosystem level, requires understanding on the type of dispersal, the dispersal range of a given species, and the dispersal mechanisms involved. Biological dispersal can be correlated to population density. The range of variations of a species' location determines expansion range.

<span class="mw-page-title-main">Sympatry</span> Biological concept

In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sharing a common range exemplifies sympatric speciation. Such speciation may be a product of reproductive isolation – which prevents hybrid offspring from being viable or able to reproduce, thereby reducing gene flow – that results in genetic divergence. Sympatric speciation may, but need not, arise through secondary contact, which refers to speciation or divergence in allopatry followed by range expansions leading to an area of sympatry. Sympatric species or taxa in secondary contact may or may not interbreed.

<span class="mw-page-title-main">Molecular ecology</span> Field of evolutionary biology

Molecular ecology is a field of evolutionary biology that is concerned with applying molecular population genetics, molecular phylogenetics, and more recently genomics to traditional ecological questions. It is virtually synonymous with the field of "Ecological Genetics" as pioneered by Theodosius Dobzhansky, E. B. Ford, Godfrey M. Hewitt, and others. These fields are united in their attempt to study genetic-based questions "out in the field" as opposed to the laboratory. Molecular ecology is related to the field of conservation genetics.

<span class="mw-page-title-main">Parapatric speciation</span> Speciation within a population where subpopulations are reproductively isolated

In parapatric speciation, two subpopulations of a species evolve reproductive isolation from one another while continuing to exchange genes. This mode of speciation has three distinguishing characteristics: 1) mating occurs non-randomly, 2) gene flow occurs unequally, and 3) populations exist in either continuous or discontinuous geographic ranges. This distribution pattern may be the result of unequal dispersal, incomplete geographical barriers, or divergent expressions of behavior, among other things. Parapatric speciation predicts that hybrid zones will often exist at the junction between the two populations.

<span class="mw-page-title-main">Hybrid zone</span> Population genetics term

A hybrid zone exists where the ranges of two interbreeding species or diverged intraspecific lineages meet and cross-fertilize. Hybrid zones can form in situ due to the evolution of a new lineage but generally they result from secondary contact of the parental forms after a period of geographic isolation, which allowed their differentiation. Hybrid zones are useful in studying the genetics of speciation as they can provide natural examples of differentiation and gene flow between populations that are at some point on the continuum between diverging populations and separate species with reproductive isolation.

The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species.

In biology, a cline is a measurable gradient in a single characteristic of a species across its geographical range. Clines usually have a genetic, or phenotypic character. They can show either smooth, continuous gradation in a character, or more abrupt changes in the trait from one geographic region to the next.

<span class="mw-page-title-main">Isolation by distance</span>

Isolation by distance (IBD) is a term used to refer to the accrual of local genetic variation under geographically limited dispersal. The IBD model is useful for determining the distribution of gene frequencies over a geographic region. Both dispersal variance and migration probabilities are variables in this model and both contribute to local genetic differentiation. Isolation by distance is usually the simplest model for the cause of genetic isolation between populations. Evolutionary biologists and population geneticists have been exploring varying theories and models for explaining population structure. Yoichi Ishida compares two important theories of isolation by distance and clarifies the relationship between the two. According to Ishida, Sewall Wright's isolation by distance theory is termed ecological isolation by distance while Gustave Malécot's theory is called genetic isolation by distance. Isolation by distance is distantly related to speciation. Multiple types of isolating barriers, namely prezygotic isolating barriers, including isolation by distance, are considered the key factor in keeping populations apart, limiting gene flow.

<span class="mw-page-title-main">Ecological speciation</span>

Ecological speciation is a form of speciation arising from reproductive isolation that occurs due to an ecological factor that reduces or eliminates gene flow between two populations of a species. Ecological factors can include changes in the environmental conditions in which a species experiences, such as behavioral changes involving predation, predator avoidance, pollinator attraction, and foraging; as well as changes in mate choice due to sexual selection or communication systems. Ecologically-driven reproductive isolation under divergent natural selection leads to the formation of new species. This has been documented in many cases in nature and has been a major focus of research on speciation for the past few decades.

Local adaptation is a mechanism in evolutionary biology whereby a population of organisms evolves to be more well-suited to its local environment than other members of the same species that live elsewhere. Local adaptation requires that different populations of the same species experience different natural selection. For example, if a species lives across a wide range of temperatures, populations from warm areas may have better heat tolerance than populations of the same species that live in the cold part of its geographic range.

<span class="mw-page-title-main">Reinforcement (speciation)</span> Process of increasing reproductive isolation

Reinforcement is a process of speciation where natural selection increases the reproductive isolation between two populations of species. This occurs as a result of selection acting against the production of hybrid individuals of low fitness. The idea was originally developed by Alfred Russel Wallace and is sometimes referred to as the Wallace effect. The modern concept of reinforcement originates from Theodosius Dobzhansky. He envisioned a species separated allopatrically, where during secondary contact the two populations mate, producing hybrids with lower fitness. Natural selection results from the hybrid's inability to produce viable offspring; thus members of one species who do not mate with members of the other have greater reproductive success. This favors the evolution of greater prezygotic isolation. Reinforcement is one of the few cases in which selection can favor an increase in prezygotic isolation, influencing the process of speciation directly. This aspect has been particularly appealing among evolutionary biologists.

This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. Overlapping and related terms can be found in Glossary of cellular and molecular biology, Glossary of ecology, and Glossary of biology.

Eukaryote hybrid genomes result from interspecific hybridization, where closely related species mate and produce offspring with admixed genomes. The advent of large-scale genomic sequencing has shown that hybridization is common, and that it may represent an important source of novel variation. Although most interspecific hybrids are sterile or less fit than their parents, some may survive and reproduce, enabling the transfer of adaptive variants across the species boundary, and even result in the formation of novel evolutionary lineages. There are two main variants of hybrid species genomes: allopolyploid, which have one full chromosome set from each parent species, and homoploid, which are a mosaic of the parent species genomes with no increase in chromosome number.

Allochronic speciation is a form of speciation arising from reproductive isolation that occurs due to a change in breeding time that reduces or eliminates gene flow between two populations of a species. The term allochrony is used to describe the general ecological phenomenon of the differences in phenology that arise between two or more species—speciation caused by allochrony is effectively allochronic speciation.

In biology, parallel speciation is a type of speciation where there is repeated evolution of reproductively isolating traits via the same mechanisms occurring between separate yet closely related species inhabiting different environments. This leads to a circumstance where independently evolved lineages have developed reproductive isolation from their ancestral lineage, but not from other independent lineages that inhabit similar environments. In order for parallel speciation to be confirmed, there is a set of three requirements that has been established that must be met: there must be phylogenetic independence between the separate populations inhabiting similar environments to ensure that the traits responsible for reproductive isolation evolved separately, there must be reproductive isolation not only between the ancestral population and the descendent population, but also between descendent populations that inhabit dissimilar environments, and descendent populations that inhabit similar environments must not be reproductively isolated from one another. To determine if natural selection specifically is the cause of parallel speciation, a fourth requirement has been established that includes identifying and testing an adaptive mechanism, which eliminates the possibility of a genetic factor such as polyploidy being the responsible agent.

References

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  15. ↑ Thomas, Yan; Bethenod, Marie-Thérèse; Pelozuelo, Laurent; Frérot, Brigitte; Bourguet, Denis (February 2003). "Genetic Isolation Between Two Sympatric Host-Plant Races of the European Corn Borer, Ostrinia Nubilalis Hubner I. Sex Pheromone, Moth Emergence Timing, and Parasitism". Evolution. 57 (2): 261–273. doi: 10.1111/j.0014-3820.2003.tb00261.x . ISSN   0014-3820. PMID   12683523. S2CID   221734366.
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  18. ↑ Habel, Jan Christian; Schmitt, Thomas (March 2012). "The burden of genetic diversity". Biological Conservation. 147 (1): 270–274. Bibcode:2012BCons.147..270H. doi:10.1016/j.biocon.2011.11.028. ISSN   0006-3207.
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  23. ↑ Habel, Jan Christian; Schmitt, Thomas (March 2012). "The burden of genetic diversity". Biological Conservation. 147 (1): 270–274. Bibcode:2012BCons.147..270H. doi:10.1016/j.biocon.2011.11.028. ISSN   0006-3207.
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