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    speciation in apple maggot flies is occurring through adaptation to different host plants that occur side by side in the same region. what is the name of the type of speciation represented by this event?

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    Species & speciation (article)

    What defines a species. How new species can arise from existing species.

    Speciation

    Species & speciation

    What defines a species. How new species can arise from existing species.

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    Key points

    According to the biological species concept, organisms belong to the same species if they can interbreed to produce viable, fertile offspring.

    Species are separated from one another by prezygotic and postzygotic barriers, which prevent mating or the production of viable, fertile offspring.

    Speciation is the process by which new species form. It occurs when groups in a species become reproductively isolated and diverge.

    In allopatric speciation, groups from an ancestral population evolve into separate species due to a period of geographical separation.

    In sympatric speciation, groups from the same ancestral population evolve into separate species without any geographical separation.

    Introduction

    On some level, the idea of a species is pretty intuitive. You don't need to be a zoologist to classify organisms like humans, giant pandas, or sunflowers into groups based on their appearance. This method works well when the species in question look very different from one another. You probably wouldn’t mistake a panda for a sunflower—unless you really needed your glasses!

    But when we get right down to it, what really make a species a species? Organisms that look alike often belong to the same species, but this isn’t always the case. I for one can't tell the African fish eagle and the bald eagle apart from the photos below. But they are, in fact, different species.

    Some species appear similar to one another. For instance, the African fish eagle and bald eagle are different species that look remarkably alike.

    Image credit: modified from Formation of new species: Figure 2 by OpenStax College, Biology CC BY 4.0

    On the flip side, organisms that belong to the same species can look very different from one another. For instance, dogs come in all shapes and sizes—from tiny Chihuahuas to massive Great Danes—but they all belong to the same species: Canis familiaris, the domestic dog.

    Individuals belonging to the same species can vary in their physical appearance. For example, the Great Dane and Chihuahua both belong to the same species, the domestic dog, though the former is much larger than the latter.

    Image credit: Big and little dog by Ellen Levy Finch, CC BY-SA 3.0

    If appearance doesn’t reliably define a species, then what does? For most eukaryotes—such as animals, plants, and fungi—scientists tend to define a species based on reproductive compatibility. That is, organisms are usually considered to be members of the same species if they can successfully reproduce with one another.

    In this article, we will explore how species are defined in greater detail. We'll also look at speciation, the process by which new species arise.

    The biological species concept

    According to the most widely used species definition, the biological species concept, a species is a group of organisms that can potentially interbreed, or mate, with one another to produce viable, fertile offspring.

    In this definition, members of the same species must have the potential to interbreed. However, that doesn't mean they have to be part of the same interbreeding group in real life. For instance, a dog living in Australia and a dog living in Africa are unlikely to meet but could have puppies if they did.

    In order to be considered to be a single species in the biological species concept, a group of organisms must produce healthy, fertile offspring when they interbreed. In some case, organisms of different species can mate and produce healthy offspring, but the offspring are infertile, can’t reproduce.

    For example, when a female horse and a male donkey mate, they produce hybrid offspring called mules. Although a mule, pictured below, is perfectly healthy and can live to a ripe old age, it is infertile and cannot have its own offspring. Because of this, we consider horses and donkeys separate species.

    Hybrids are the offspring of two species. A mule is the hybrid offspring of a female horse and male donkey. Because mules are sterile, they are not classified as a distinct species.

    Image credit: Juancito by Dario u, public domain

    The biological species concept connects the idea of a species to the process of evolution. Because members of a species can interbreed, the species as a whole has a common gene pool, a collection of gene variants.

    On the other hand, genes are not exchanged between different species. Even if organisms of different species combine their DNA to make offspring, the offspring will be sterile, unable to pass on their genes. Because of this restricted gene flow, each species evolves as a group distinct from other species.

    Source : www.khanacademy.org

    Speciation

    Speciation

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    For the electrochemical phenomenon, see Ion speciation.

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    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.[1][2][3] Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book .[4] He also identified sexual selection as a likely 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, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry, agriculture, or laboratory experiments.[] Whether genetic drift is a minor or major contributor to speciation is the subject of much ongoing discussion.

    Rapid sympatric speciation can take place through polyploidy, such as by doubling of chromosome number; the result is progeny which are immediately reproductively isolated from the parent population. New species can also be created through hybridization, followed by reproductive isolation, if the hybrid is favoured by natural selection.

    Contents

    1 Historical background

    1.1 Darwin's dilemma: why species exist

    1.2 Effect of sexual reproduction on species formation

    2 Modes 2.1 Allopatric 2.2 Peripatric 2.3 Parapatric 2.4 Sympatric

    3 Methods of selection

    3.1 Reinforcement 3.2 Ecological

    3.3 Sexual selection

    4 Artificial speciation

    5 Genetics

    5.1 Speciation via polyploidy

    5.2 Hybrid speciation

    5.3 Gene transposition

    6 Rates

    6.1 Punctuated evolution

    7 See also 8 References 9 Bibliography 10 Further reading 11 External links

    Historical background[edit]

    Main article: History of speciation

    In addressing the origin of species, there are two key issues:

    the evolutionary mechanisms of speciation

    how the separateness and individuality of species is maintained

    Since Charles Darwin's time, efforts to understand the nature of species have primarily focused on the first aspect, and it is now widely agreed that the critical factor behind the origin of new species is reproductive isolation.[5]

    Darwin's dilemma: why species exist[edit]

    In (1859), Darwin interpreted biological evolution in terms of natural selection, but was perplexed by the clustering of organisms into species.[6] 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?

    —  (1859), chapter 6[6]

    This dilemma can be described as the absence or rarity of transitional varieties in habitat space.[7]

    Another dilemma,[8] 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 clearly defined species actually do exist in nature in both space and time implies that some fundamental feature of natural selection operates to generate and maintain species.[6]

    Effect of sexual reproduction on species formation[edit]

    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.[9][10][11][12][13] The cost of rarity arises as follows. If, on a resource gradient, a large number of separate species evolve, each exquisitely adapted to a very narrow band on that gradient, each species will, of necessity, consist of very 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 (at the expense of one or other of its neighboring species, if the environment is saturated), this will immediately 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, and therefore form pairs less frequently than the larger species. This has a snowball effect, with large species growing at the expense of the smaller, rarer species, eventually driving them to extinction. Eventually, only a few species remain, each distinctly different from the other.[9][10][12] The cost of rarity not only involves the costs of failure to find a mate, but also indirect costs such as the cost of communication in seeking out a partner at low population densities.

    Source : en.wikipedia.org

    BIOL2007

    BIOL 2007 - THE ORIGINS OF SPECIESHow does speciation happen?

    There are many definitions of species, but they all boil down to the fact that species are different at a number of gene loci. A pair of different species, even when in contact, usually form a (i.e. two clusters of individuals); they can clearly be distinguished from one another by some morphological, genetic, ecological or behavioural traits, though there may be some overlap and/or hybridization between them. In contrast, members of a single species when in contact present a distribution (only one group of organisms can be distinguished).

    How are these bimodal distributions of genotypes and phenotypes caused?

    : The origins of species, (speciation), might be due to either random forces, such as mutation and drift, or deterministic forces, i.e. natural selection.: Speciation might also occur in various kinds of geographical situations: sympatric, parapatric, or allopatric. Whatever people may have told you before, these geographical situations are not "mechanisms of speciation", they simply tell you where, not how they occur.

    We will here explore both the evolutionary causes of speciation, and geographical milieu in which they can occur. Here is a brief summary of what we know (this is a kind of lecture summary):

    (my opinion - you may disagree!)

    Deeply suspect! If occurs, probably slow, needs allopatry

    (polyploidy) Known

    Known Known, but rare? Suspected

    Possible, contested Dubious, contested

    (my opinion - you may disagree!) Known, but rare?  Maybe not! Known to give partial isolation; complete would not be surprising Known; slow?

    The lecture will attempt to explain how we know (or not!) these things.

    General rules of speciation

    Evidence so far (see , and lectures) tells us that:

    1) Speciation is (usually), and involves . We know this because hybrid zones often separate forms that differ at many loci (allozyme and molecular differences, as well as chromosomal, morphological, ecological and behavioural differences), even though we do NOT consider these hybridizing forms to be separate species, but instead geographical races or subspecies. Species can overlap without losing their identity in a parapatric hybrid zone or in sympatry, whereas hybridizing races do not, it stands to reason that species should differ at even more loci than races. Ayala's work in the 1970s showed this to be true for enzyme proteins in .  Since then, many other molecular studies have shown the same thing.

    A major exception to this "gradual speciation" rule is speciation via polyploidy, which is sudden (see Biodiversity and Species).  See also the interesting website "Observed instances of speciation" for rapid examples that have been seen to occur recently.  Most cases were plant polyploidy (see below), which is an exception to the general gradual rule.  See also the case of the apple maggot fly, below.

    2) Speciation involves . In order to maintain a bimodal distribution of phenotypes/genotypes of two species in sympatry, multilocus intermediates must be either unfit or never produced. For example, and have high fitness, whereas and genotypes are less fit.  So and collaborate, or are in their effects on fitness.

    3) A third general rule is that there is rule for speciation. Species differ at loci that cause or selection against hybrids, as well as at loci affecting . Speciation must have required evolution at these same loci. To remind you, selection is caused by geographic variation in the ; selection may be caused by , against rare forms, and, perhaps most importantly, on many loci.Variation at mate choice loci may be affected by sexual selection among other factors. These are the types of selection acting on loci that affect .

    Cline theory predicts that loci under selection may diverge over quite short distances, small multiples of cline widths, = 1.73/measures gene flow distance, and measures the strength of selection. So, there is no particular reason why these might not diverge in . This is also true in nature; although strong selection in N. Wales keeps peppered moths peppery-coloured, and strong selection in Liverpool keeps peppered moths melanic, no was required for divergence to take place. All that was required was that the spatial scale of selection was somewhat greater than

    4) I have stressed repeatedly that . There is no fundamental difference between species and races and morphs; species just have more of the same type of genetic divergence we have already encountered in this course. The only difference is that in species, genetic divergence and selection is sufficiently intense so that two distinct populations can be maintained in sympatry.

    Additional potential evolutionary causes of speciation

    I would like here to mention four important potential causes of speciation, in addition to the ordinary forces already studied:

    1) . We have already treated this in Chromosomal doubling has the capability for instantaneously producing new species. The speciation is sympatric.

    In polyploidy, a failure of cell division can lead, at a stroke, to a new species that produces sterile triploid hybrids with all diploids. The new species is, however, a . Without selfing, it has no-one with whom to mate. Plants and more amorphous animals are predominant among polyploids because their development is perhaps more resilient to disturbance, and because they can self. However, some sexual animals, such as most of the Salmonidae (trout and salmon family) are also polyploids.

    Source : www.ucl.ac.uk

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