Reproductive isolation: definition, causes. Forms of reproductive isolation: examples

Panmictic organisms (reproducing sexually) is a kind of – is a set of organisms similar in a whole range of signs, are able to freely interbreed with the formation of fertile offspring. The concept of insulation is applied in the context of microevolution, as it is called, is speciation. Reproductive isolation starts the process of formation of new species and finishes it. But not all forms of this phenomenon will lead to the emergence of a new kind, as not every final isolation leads to reproductive isolation of populations.

Isolating mechanisms in the evolution

Within a species, there are groups-populations. It population as the unit of microevolution serve as material for the formation of new species, different from the original. Within a species, between populations there is an exchange of genetic material during reproduction. That is called reproductive ability of organisms. When, for whatever-reason, this exchange between populations within a species is limited or impossible, they say, that it was reproductive isolation. The definition of this evolutionary mechanism is that individuals from different populations are unable to produce offspring. The history of the emergence of a new kind of – is a chain of different types of reproductive isolation, successive or overlapping each other, making the separation of the population irreversible.

Reproductive Isolation: classification

There are several concepts in the classification of the varieties of isolation of populations. The different criteria taken for the main feature, lend some confusion to this issue. Accept that reproductive isolation as a permanent limitation of panmixia (free crossing) - this is the last stage, the final speciation. Supporters of this view on the species forming the insulation was known to evolutionary biologists F. G. Dobzhansky(1900-1975), E. Mayr (1904-2005.). Mechanisms of reproductive isolation in this approach are divided into three groups:

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• Spatial separation (geographic);
• Environmental isolation (mechanisms of the environment);
• Actually the reproductive mechanism, including compulation (before the formation of the zygote) and posleoperazionny (mating occurs but the egg is fertilized or not, or dies, or the hybrids are sterile) barriers.

When any mechanism is achieved by limiting panmixia: full or partial. Briefly, each group will examine the forms of reproductive isolation. The examples that illustrate them, will help to understand the essence of a form.

Spatial mechanisms, isolation of populations

The isolation Mechanism is associated with various changes in the landscape (the emergence of obstacles in the form of mountain ranges or rivers) or in its distribution over vast territories. In violation of gene flow between the separated populations reproductive isolation occurs. The most famous example of this phenomenon with the formation of new species can be considered Bunkov island species of the Galapagos Islands, which became one of Charles Darwin's “the Origin of species by means of natural selection”. Or example blue magpies, one population of which lives in China and another in Spain.

Ecological mechanisms of isolation

The Reasons for the reproductive isolation of this type is associated with the difference of the conditions of reproduction of populations of the same species living symmetrically, that is in the same area. For example, breeding seasons or flowering do not coincide. On the California coast symmetrically there are two kinds of pine trees: one species of pollen is showered in February and another in April. Seasonal environmental isolation for them to become reproductive. An example of reproductive isolation, but resulting from different forage bases, demonstrate three species of Antarctic seals that have occurred from one phylogenetic ancestor. Seal Wedelia eats only fish, sea leopard – penguins and seals, and the seal Ross-cephalopods.

Compulation forms of reproductive isolation

Mechanical insulation – the failure of pairing caused by the different structure of the reproductive or copulatory organs. For example, different types of sage have different shapes of the flower and pollinated by other bees. The same correlation between orchids and hummingbirds. Interspecific mating of Drosophila leads to injury or even death of a partner.

Ethological isolation – not mating due to differences in sexual behavior (courtship, singing, dancing, luminosity, or the difference of pheromones). For example, closely related species of fireflies while inviting females to mate different flash (with different frequency and duration). You can also mention in this context species-specific songs of sparrows and frogs. And about the mating rituals of birds they know everything.

GENETIChESKAYa insulation – the lack of interaction of gametes or destruction of gametes. The existence of this type of insulation is proven experimentally. For example, two species of sea urchins with external fertilization crossed American genetics Denis and Brachet. The egg was fertilized but the embryo died at an early stages of gastrulation.

Posleoperazionny forms of reproductive isolation

This refers to the inviability of the fertilized egg and the death of the embryo in the early stages of ontogenesis. Or the death of a born baby (or individuals) to achieve sexual maturity. A very close concept to geneticheskoi isolation.

The Sterility of hybrid individuals

The majority of the surviving animals interspecific hybrids are sterile, i.e. not able to produce offspring. The exception may be polistirolnye hybrids. The mechanism of this phenomenon is quite complicated, based on genetic, chromosomal, or cytological reasons. We will give only examples of interspecific hybrids, which are known to all.

A hybrid of a donkey and a Mare-mule. He's bigger than a donkey and smaller horses, in addition, animals are easier to contain. Hybrids of closely related subspecies of dog and wolf (volkosob, poluvolk) possess more developed intuition and stamina than an ordinary dog. Many of aquarium fish – hybrid forms (colorful aulonocara). They are beautiful, larger than the parent forms, but at purchase it is necessary to clarify the origin of the fish, otherwise, can't wait for offspring. Everyone knows that the seeds of cultivated plants (tomatoes, cucumbers), marked with symbol F-1 is a hybrid form. The fruits of these plants are not left on the seeds.