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How Can Geography Lead To Reproductive Isolation

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How Can Reproductive Barriers Lead To Speciation


Reproductive isolation represents a breakdown in the ability to reproduce successfully with sexual partners of another type of organism and speciation requires a build up of reproductive isolation between diverging types of organism until gene flow is sufficiently rare or ineffective that the entities are considered

Evaluation Of Morphological Variation

Principal component axes I and II cumulatively explain 89% of the morphological variation in the characters measured. PC I explained 61% of the variance while PC II explained another 28%. The morphological gradient along PC I shifted from negative loadings for longest spine and spine count to positive loadings for head/total length PC axis II had a gradient of longest spine to head/total length . PerMANOVA on wildcaught amphipods showed that all five wildcaught amphipod populations were morphologically distinct . Wildcaught versus the commongarden amphipods showed that all commongarden amphipods differed significantly from their wildcaught ancestors except for the SMS population . Despite an apparent shift in morphology after five generations in captivity under essentially identical conditions, all commongarden populations remained morphologically distinct from each other at p < .05 . Distribution of centroids in PCA space was not found to be significantly correlated to genetic distance .

Phylomorpho plot of population centroids with phylogenetic relationship. Genetic similarity is not related to distribution of centroids in principal components analysis space. Decimals along branches represent the Bayesian model inferred number of substitutions

Reproductive Isolation As A Complex Trait

It is important to note that different mechanisms of reproductive isolation are not mutually exclusive. Between any population pair, many mechanisms may coincide such that total reproductive isolation is a composite of mechanisms that reduce the probability of mating between different populations, reduce the probability of fertilization should mating happen, and reduce the success of hybrids should fertilization happen. More over, as we will see below, the evolution of one reproductive isolation mechanism can profoundly impact the evolution of other reproductive barriers. Hence, it many natural systems it is critical not to just examine different mechanisms in isolation, but to also consider how different mechanisms interact to keep gene pools separated from one another.

Figure 11.11: Different mechanisms of reproductive isolation often act in concert and can influence each other evolutionarily.

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What Is A Species

  • Morphological species concept:Oak trees look like oak trees, tigers look like tigers. Morphology refersto the form and structure of an organism or any of its parts. The morphologicalspecies concept supports the widely held view that “members of a speciesare individuals that look similar to one another.” This school of thoughtwas the basis for Linneaus’ original classification, which is still broadlyaccepted and applicable today.

Mimicry complexes supplied furtherevidence against the concept, as organisms of the same species can lookvery different, depending upon where they are reared or their life cyclestage .

The morphological species conceptwas replaced by another viewpoint that puts more emphasis on the biologicaldifferences between species.

  • Biological species concept: Thisconcept states that “a species is a group of actually or potentially interbreedingindividuals who are reproductively isolated from other such groups.”

This concept also emphasized thata species is an evolutionary unit. Members share genes with other membersof their species, and not with members of other species.

Although this definition clearlyis attractive, it has problems. Can you test it on museum specimens orfossil data? Can it explain the existence of species in a line of descent,such as the well-known lineage of fossil horses? Obviously not.

So what is the best way to definea species?

How Does Geographic Isolation Contribute To Evolution

Reproductive Isolation

Geographic isolation of a group of organisms eventually stops gene flow from other groups of same species. Thus isolated group evolves by accumulating new mutations not to be found in members of related groups.


All members of a species form a single population. But all organisms of a single species would not be confined in a single geographic location though they may interact and interbreed occasionally.

In nature, organisms are distributed in different areas, forming separate subpopulations. Each subpopulation thus maintains a gene pool. When members of different subpopulations migrate and interbreed genes are exchanged between gene pools. Higher the gene flow, more alike are the two subpopulations.

Hence geographical isolation stops gene flow between subpopulations. New mutations may appear in such isolated subpopulation giving them unique identity.

Eventually a geographically isolated subpopulation would become genetically very different. As a result members may fail to successfully interbreed with members of related parental group. Thus long geographical isolation may lead to reproductive isolation. In such case, the isolated subpopulation gets elevated to designation of a species.

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How Does Reproductive Isolation Cause Speciation

Gene flow occurs between populations of the same species but not between populations of different species. Members of a species can interbreed, so the species as a whole shares a common gene pool. On the other hand, members of different species usually do not interbreed. If they do, they will produce inviable or sterile offspring and will be unable to pass on their genes. This means that the presence or absence of gene flow can distinguish one species from another.

Reproductive isolation mechanisms limit or prevent gene flow between different species. This causes the allele frequencies of the groups to become more and more different from each other. If the groups do not interbreed for a long period of time, the differences between their alleles become greater because of the differences in their environment . Eventually, the groups will become genetically divergent, forming new species.

This process is illustrated in Figure 4 below. A single species population splits into two populations . The black lines represent gene flow. As we can see in the diagram, the two populations become reproductively isolated, and over time, they become two distinct species.

Figure 4. This diagram illustrates how reproductive isolation takes place in a population. Source: Andrew Z. Colvin, CC BY-SA 4.0, via Wikimedia Commons.

Where Is The Mystery In Speciation

The answer to this question is a topic for a different essay. However, it involves the second part of the speciation process, namely how characters evolve during the speciation process, or as I termed it above, the biology of speciation. Some species concepts, such as the BSC, require a complicated set of events to occur before two diagnostically different populations are recognized as two species, and therefore inferring that speciation has occurred . There is a myriad of ways in which two allopatric populations can acquire the character differences they need to be reproductively isolated. There are few if any generalities in this process across animals and plants, and what generalities exist are limited to specific groups. It is my opinion that because there are so few generalities, speciation has been considered mysterious. In short, if you realize that two species can become reproductively isolated by unique means, there is no mystery, only a lack of generality. The biology of speciation, then, is not a mystery either. It is just that the biology of speciation is more complex than the geography of speciation. This in my opinion does not qualify as a biological mystery, it just reveals once more the complex nature of biological variation that so intrigues us with understanding life in the first place.

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Evolution And Its Many Forms

The word “evolution” does not applyexclusively to biological evolution. The universe and our solar systemhave developed out of the explosion of matter that began our known universe.Chemical elements have evolved from simpler matter. Life has evolved fromnon-life, and complex organisms from simpler forms. Languages, religions,and political systems all evolve. Hence, evolution is an appropriate themefor a course on global change.

The core aspects of evolution are”change” and the role of history, in that past events have an influenceover what changes occur subsequently. In biological evolution this mightmean that complex organisms arise out of simpler ancestors – though beaware that this is an over-simplification not acceptable to a more advanceddiscussion of evolution.

A full discussion of evolution requiresa detailed explanation of genetics, because science has given us a goodunderstanding of the genetic basis of evolution. It also requires an investigationof the differences that characterize species, genera, indeed the entiretree of life, because these are the phenomena that the theory of evolutionseeks to explain.

We will begin with observed patternsof similarities and differences among species, because this is what Darwinknew about. The genetic basis for evolution only began to be integratedinto evolutionary theory in the 1930’s and 1940’s. We will add geneticsinto our understanding of evolution through a discussion activity.

Types Of Reproductive Isolation

Reproductive Isolation and Speciation in Lizards HHMI BioInteractive Video

This suggests a simple and usefuldichotomy, between pre-mating or prezygotic reproductive isolating mechanisms, and post-mating or postzygotic isolatingmechanisms. Remember that a zygote is the cell formed by the union of twogametes and is the basis of a developing individual.

Prezygotic isolating mechanisms

  • Ecological isolation: Species occupydifferent habitats. The lion and tiger overlapped in India until 150 yearsago, but the lion lived in open grassland and the tiger in forest. Consequently,the two species did not hybridize in nature .
  • Temporal isolation: Species breed atdifferent times. In North America, five frog species of the genus Ranadiffer in the time of their peak breeding activity.
  • Behavioral isolation: Species engagein distinct courtship and mating rituals .
  • Mechanical isolation: Interbreedingis prevented by structural or molecular blockage of the formation of thezygote. Mechanisms include the inability of the sperm to bind to the eggin animals, or the female reproductive organ of a plant preventing thewrong pollinator from landing.
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    How Does Geographical And Reproductive Isolation Lead To Speciation

    The geographical isolation is the physical separation of two populations by the geographical barriers. This occurs through adaptive radiation and allopatric speciation. The reproductive isolation is the separation of two populations of the same species preventing interbreeding and production of a fertile offspring.

    Polyploidization And Instantaneous Speciation

    Polyploidization is a form of mutation that leads to the duplication of entire genomes, typically due to meiotic errors leading to unreduced gametes. Fertilization of unreduced gametes with other unreduced gametes causes the formation of fertile polyploid lineages . Polyploid lineages are immediately isolated from their ancestral lineage because of dysfunctional chromosome complements in crosses between individuals of different ploidy. Such auto-polyploid speciation is particularly common in plants and other organisms for which self-fertilization is possible, because the combination of two unreduced gametes is a strong limiting factor in the formation of polyploids. Accordingly, up to 4 % of plant species are thought to have arisen through auto-polyploid speciation , while this phenomenon is rare in animals.

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    What Is Geographic Isolation In Evolution

    Geographic isolation is a term that refers to a population of animals, plants, or other organisms that are separated from exchanging genetic material with other organisms of the same species. Typically geographic isolation is the result of an accident or coincidence.

    What is the role of geography in evolution?

    Patterns pertaining to the geographic distribution of organisms and patterns in the fossil record played a fundamental role in convincing Darwin and other scientists that evolution had happened, and they still play an important role today in providing insights into the evolutionary process.

    Which one is the important consequence of geographical isolation?

    Origin of new specie from ancestral specie because of geographical isolation followed by Reproductive isolation is known as Allopatric speciation. So, the correct answer is Speciation through reproductive isolation.

    How Can Geographic Isolation Lead To Evolution Of New Species

    Genomics of Divergence along a Continuum of Parapatric Population ...

    The development of new species due to geographical separation is known as allopatric speciation. With the two groups of organisms no longer interbreeding, their gene pools become separate. Genes are no longer exchanged between the two groups, allowing them to diverge into two different species.

    How does geographic isolation affect species?

    Islands epitomize allopatric speciation, where geographic isolation causes individuals of an original species to accumulate sufficient genetic differences to prevent them breeding with each other when they are reunited.

    How does geographic isolation contribute to speciation quizlet?

    The geographic isolation of the finches on different islands meant that each islands environment selected for traits that were beneficial on that particular island. Over time, genetic differences accumulated in the isolated populations, leading to many distinct finch species.

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    What Is The Difference Between Geographic And Reproductive Isolation

    The geographic isolation is one of the types of reproductive isolation. Therfore, there is not much difference between geographic isolation and reproductive isolation other than the specific categorization due to the mechanism of isolation. Geographic isolation separates individuals of the closely related species from mating by geographical barriers such as mountains, water bodies, etc. Reproductive isolation is a collection of mechanisms, which is critical for speciation in order to prevent different species from producing fertile offspring.

    What Can Cause Geographic Isolation

    This can occur when rivers change course, mountains rise, continents drift, or organisms migrate. The geographic barrier isnt necessarily a physical barrier that separates two or more groups of organisms it might just be unfavorable habitat between the two populations that keeps them from mating with one another.

    How does reproductive isolation play a role in speciation?

    Reproductive isolation is instrumental in speciation as it is necessary for the genetic integrity of emerging species. Fungi do not always adhere to this biological species concept, which defines species according to their reproductive boundaries.

    How can isolation lead to the formation of new species?

    Both geographical and reproductive isolation lead to the speciation in which an ancestral species to divide into new, distinct species. Both geographical and reproductive isolation can occur due to the separation of two populations by geographical barriers.

    What does reproduction isolation within a species cause?

    Reproductive isolation driving evolution of species. Also, speciation can occur due to reproductive isolation. This can be caused by mating differences, sterility or environmental barriers that eventually lead to the adaptive splitting into two species. However, reproductive isolation is not sufficient but internal barriers to gene flow are required for speciation to evolve.

    What is reproductive isolation caused by?

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    A Randomized Sampling Of Phenotypic Variation

    To characterize standing phenotypic variation, individuals growing at least 5 meters apart were sampled at several sites per canga . For flower size and shape measurements, a single flower per individual was collected sepals, anthers, and styles were removed. Intact flower corollas or dissected flowers were photographed from the front and the side next to a ruler. Digital flower images were used for trait measurements. For the leaf length/width ratio, five leaves per individual were measured with a ruler for the leaf lamina length along midvein and maximal width. The sample sizes are summarized in Supplementary Table .

    Practical Skills: Interpreting Structure Plots


    From a coding perspective, there are no new graph types you need to learn about for this exercise you will be able to apply skills that you have already learned over the past chapters. However, you will have a chance to explore some population genetic data that are commonly used to investigate ongoing speciation with gene flow. Specifically, analyses of population structure use genetic data from multiple loci to test hypotheses about the most likely number of genetically distinct clusters in a set of samples. These analyses try to identify the systematic differences in allele frequencies that arise between subpopulations as a consequence of nonrandom mating. Results from analyses of population structure are typically visualized using stacked bar plots, where each bar corresponds to an individual, and bar segments are proportional to the probability of an individual belonging to a particular cluster . Sounds abstract? Lets look at some concrete scenarios.

    At the other end of the extreme, we might find very strong population structure, with two randomly mating populations but no interbreeding between them. In that case, we may be able to assign each individual to one of two clusters with 100 % probability. This scenario is illustrated in Figure 11.24B individuals from each habitat are distinct and clearly assignable to one of two clusters based on their multilocus genotype.

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    What Types Of Reproductive Isolation May Have Been

    These include temporal isolation, ecological isolation, behavioral isolation, and mechanical isolation.

    How did geographic isolation affect the diversity?

    Geographic isolation is known to contribute to divergent evolution, resulting in unique phenotypes. Oftentimes morphologically distinct populations are found to be interfertile while reproductive isolation is found to exist within nominal morphological species revealing the existence of cryptic species.

    What are the 3 types of reproductive isolation?

    These mechanisms include physiological or systemic barriers to fertilization.

    • Temporal or habitat isolation.
    • Gametic isolation.

    How the geographical and reproductive isolation of organisms gradually leads to speciation?

    Geographical and reproductive isolation of organisms gradually leads to speciation. Solution : Every species survives in specific geographical conditions. The requirements of food and habitat is specific for each species. Their reproductive ability and period is also different .

    Temperament And Temporal Reproductive Isolation

    Reproductive isolation can occur when individuals or populations exhibit differences in the timing of various activities, including foraging or mating . Well known examples include differences in hatching schedule in Enchenopa treehoppers found on different host plants and differences in spawning seasonality in salmon . Individuals with different personalities are predicted to become reproductively isolated when personality influences temporal activity, and when the timing of these activities in turn results in a reduction in mating encounters. For example, individuals that have bold behavioral types might be more likely to feed, or to mate, during times of high-predation risk than individuals with shy temperament types that are less likely to be active during risky periods. Unfortunately, little work has explored the relationship between personality and temporal activity levels, and no work to my knowledge has explored the connection between personality-dependent differences in the timing of activity and reproductive isolation. This offers a promising area for future research.

    D. Ortiz-Barrientos, in, 2016

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