How can isolation lead to the formation of new species

Scientists call such organisms members of the same biological species. A species is a group of individual organisms that interbreed and produce fertile, viable offspring.

According to this definition, one species is distinguished from another when, in nature, it is not possible for matings between individuals from each species to produce fertile offspring.

Members of the same species share both external and internal characteristics, which develop from their DNA. The closer relationship two organisms share, the more DNA they have in common, just like people and their families. Organisms of the same species have the highest level of DNA alignment and therefore share characteristics and behaviors that lead to successful reproduction.

For example, even though domestic dogs Canis lupus familiaris display phenotypic differences, such as size, build, and coat, most dogs can interbreed and produce viable puppies that can mature and sexually reproduce Figure 1. Figure 1. The a poodle and b cocker spaniel can reproduce to produce a breed known as c the cockapoo. In other cases, individuals may appear similar although they are not members of the same species.

For example, even though bald eagles Haliaeetus leucocephalus and African fish eagles Haliaeetus vocifer are both birds and eagles, each belongs to a separate species group Figure 2. If humans were to artificially intervene and fertilize the egg of a bald eagle with the sperm of an African fish eagle and a chick did hatch, that offspring, called a hybrid a cross between two species , would probably be infertile—unable to successfully reproduce after it reached maturity.

Different species may have different genes that are active in development; therefore, it may not be possible to develop a viable offspring with two different sets of directions. Thus, even though hybridization may take place, the two species still remain separate. Figure 2. The a African fish eagle is similar in appearance to the b bald eagle, but the two birds are members of different species. Fish and Wildlife Service. Populations of species share a gene pool: a collection of all the variants of genes in the species.

Again, the basis to any changes in a group or population of organisms must be genetic for this is the only way to share and pass on traits. When variations occur within a species, they can only be passed to the next generation along two main pathways: asexual reproduction or sexual reproduction. The change will be passed on asexually simply if the reproducing cell possesses the changed trait.

For the changed trait to be passed on by sexual reproduction, a gamete, such as a sperm or egg cell, must possess the changed trait. In other words, sexually-reproducing organisms can experience several genetic changes in their body cells, but if these changes do not occur in a sperm or egg cell, the changed trait will never reach the next generation. Only heritable traits can evolve. Therefore, reproduction plays a paramount role for genetic change to take root in a population or species.

In short, organisms must be able to reproduce with each other to pass new traits to offspring. The biological definition of species, which works for sexually reproducing organisms, is a group of actually or potentially interbreeding individuals. There are exceptions to this rule. Many species are similar enough that hybrid offspring are possible and may often occur in nature, but for the majority of species this rule generally holds.

In fact, the presence in nature of hybrids between similar species suggests that they may have descended from a single interbreeding species, and the speciation process may not yet be completed. Given the extraordinary diversity of life on the planet there must be mechanisms for speciation: the formation of two species from one original species. Darwin envisioned this process as a branching event and diagrammed the process in the only illustration found in On the Origin of Species Figure 3a.

Compare this illustration to the diagram of elephant evolution Figure 3b , which shows that as one species changes over time, it branches to form more than one new species, repeatedly, as long as the population survives or until the organism becomes extinct. Figure 3. The diagram shows similarities to phylogenetic charts that are drawn today to illustrate the relationships of species. For speciation to occur, two new populations must be formed from one original population and they must evolve in such a way that it becomes impossible for individuals from the two new populations to interbreed.

Biologists have proposed mechanisms by which this could occur that fall into two broad categories. Biologists think of speciation events as the splitting of one ancestral species into two descendant species. There is no reason why there might not be more than two species formed at one time except that it is less likely and multiple events can be conceptualized as single splits occurring close in time.

A geographically continuous population has a gene pool that is relatively homogeneous. Gene flow, the movement of alleles across the range of the species, is relatively free because individuals can move and then mate with individuals in their new location. Thus, the frequency of an allele at one end of a distribution will be similar to the frequency of the allele at the other end.

When populations become geographically discontinuous, that free-flow of alleles is prevented. When that separation lasts for a period of time, the two populations are able to evolve along different trajectories. Thus, their allele frequencies at numerous genetic loci gradually become more and more different as new alleles independently arise by mutation in each population.

Typically, environmental conditions, such as climate, resources, predators, and competitors for the two populations will differ causing natural selection to favor divergent adaptations in each group. Figure 4. The northern spotted owl and the Mexican spotted owl inhabit geographically separate locations with different climates and ecosystems. The owl is an example of allopatric speciation. Isolation of populations leading to allopatric speciation can occur in a variety of ways: a river forming a new branch, erosion forming a new valley, a group of organisms traveling to a new location without the ability to return, or seeds floating over the ocean to an island.

The nature of the geographic separation necessary to isolate populations depends entirely on the biology of the organism and its potential for dispersal. If two flying insect populations took up residence in separate nearby valleys, chances are, individuals from each population would fly back and forth continuing gene flow. However, if two rodent populations became divided by the formation of a new lake, continued gene flow would be unlikely; therefore, speciation would be more likely.

Biologists group allopatric processes into two categories: dispersal and vicariance. Dispersal is when a few members of a species move to a new geographical area, and vicariance is when a natural situation arises to physically divide organisms.

Scientists have documented numerous cases of allopatric speciation taking place. For example, along the west coast of the United States, two separate sub-species of spotted owls exist.

The northern spotted owl has genetic and phenotypic differences from its close relative: the Mexican spotted owl, which lives in the south Figure 4. Additionally, scientists have found that the further the distance between two groups that once were the same species, the more likely it is that speciation will occur. This seems logical because as the distance increases, the various environmental factors would likely have less in common than locations in close proximity.

Consider the two owls: in the north, the climate is cooler than in the south; the types of organisms in each ecosystem differ, as do their behaviors and habits; also, the hunting habits and prey choices of the southern owls vary from the northern owls. These variances can lead to evolved differences in the owls, and speciation likely will occur. Mayr, E. Systematics and the Origin of Species. The Evolutionary Synthesis.

Niemiller, M. Recent divergence with gene flow in Tennessee cave salamanders Plethodontidae: Gyrinophilus inferred from gene genealogies. Molecular Ecology 17 , — Nosil, P. Host-plant adaptation drives the parallel evolution of reproductive isolation. Nature , — Ecological explanations for incomplete speciation. Divergent selection and heterogeneous genomic divergence. Molecular Ecology 18 , — Panhuis, T.

Sexual selection and speciation. Ramsey, J. Pathways, mechanisms and rates of polyploid formation in flowering plants. Annual Review of Ecology, Evolution, and Systematics 29 , — Ritchie, M.

Annual Review of Ecology, Evolution, and Systematics 38 , 79— Rundle, H. Ecological speciation. Ecology Letters 8 , — Schluter, D. Ecology and the origin of species. Evidence for ecological speciation and its alternative.

Science , — Seehausen, O. Speciation through sensory drive in cichlid fish. Turner, T. Genomic islands of speciation in Anopheles gambiae. PLoS Biology 3 , e On the origin of species by natural and sexual selection. Via, S. Sympatric speciation in animals: The ugly duckling grows up. The Hardy-Weinberg Principle.

Evolution Introduction. Life History Evolution. Mutations Are the Raw Materials of Evolution. Speciation: The Origin of New Species. Avian Egg Coloration and Visual Ecology. The Ecology of Avian Brood Parasitism. The Maintenance of Species Diversity. Neutral Theory of Species Diversity. Population Genomics.

Semelparity and Iteroparity. Geographic Mosaics of Coevolution. Comparative Genomics. Cybertaxonomy and Ecology. Ecological Opportunity: Trigger of Adaptive Radiation. Evidence for Meat-Eating by Early Humans. Resource Partitioning and Why It Matters. The Evolution of Aging. Citation: Safran, R. Nature Education Knowledge 3 10 How do new species form? Like most areas of Evolutionary Biology, research related to the formation of new species - 'speciation ' - is rich in historical and current debate.

Here, we review both early and modern views on speciation, starting with Darwin and finishing with current genomics-era insights. Aa Aa Aa. Darwin's "Mystery of Mysteries". The Modern Synthesis. Barriers to reproduction. The role of geography in speciation. Biologists have long been fascinated with — and sought to explain — the origin and maintenance of biological diversity within and among species. Natural selection is generally recognized as a central mechanism of evolutionary change within species.

Thus, natural selection plays a major role in generating the array of phenotypic and genetic diversity observed in nature. But to what extent is selection also responsible for the formation of new species i. To what extent do phenotypic and species diversity arise via the same processes, as proposed by Darwin? Figure 4. Ecological speciation in host-plant associated populations of Timema cristinae walking-stick insects individual populations feed on either the Ceanothus spinosus host plant or on Adenostoma fasciculatum.

The role of sexual selection in speciation. A view that is becoming increasingly popular is that sexual selection, or selection related to variation in reproductive success, plays a role in speciation Panhuis et al.

This model suggests that differential patterns of trait variation related to reproductive success within populations contribute to the reproductive isolation among populations. A compelling example is related to the explosive radiation of cichlid fishes in the African Rift Lakes, where populations with overlapping distributions are diverging as a function of the differential preference of male color in mate selection Seehausen et al.

Some models of speciation do not include a role for selection of any sort, but rather invoke a key role for chance events. Current views: Mutation-order vs. A lack of strong examples for speciation by genetic drift, yet evidence for ecologically-similar species pairs Price , has led to the development of a powerful alternative mechanism to ecological speciation. Prezygotic barriers block reproduction prior to formation of a zygote, whereas postzygotic barriers block reproduction after fertilization occurs.

For a new species to develop, something must cause a breach in the reproductive barriers. Sympatric speciation can occur through errors in meiosis that form gametes with extra chromosomes polyploidy.

Autopolyploidy occurs within a single species, whereas allopolyploidy occurs between closely related species. Which variable increases the likelihood of allopatric speciation taking place more quickly? Which condition is the basis for a species to be reproductively isolated from other members?

Which situation is not an example of a prezygotic barrier? Why do island chains provide ideal conditions for adaptive radiation to occur? Organisms of one species can arrive to an island together and then disperse throughout the chain, each settling into different niches and exploiting different food resources to reduce competition. Two species of fish had recently undergone sympatric speciation.

The males of each species had a different coloring through which the females could identify and choose a partner from her own species. After some time, pollution made the lake so cloudy that it was hard for females to distinguish colors.

What might take place in this situation? It is likely the two species would start to reproduce with each other. Depending on the viability of their offspring, they may fuse back into one species. The formation of gametes with new n numbers can occur in one generation. After a couple of generations, enough of these new hybrids can form to reproduce together as a new species.

Skip to content Evolution and the Origin of Species. Learning Objectives By the end of this section, you will be able to: Define species and describe how species are identified as different Describe genetic variables that lead to speciation Identify prezygotic and postzygotic reproductive barriers Explain allopatric and sympatric speciation Describe adaptive radiation. Species and the Ability to Reproduce A species is a group of individual organisms that interbreed and produce fertile, viable offspring.

The a poodle and b cocker spaniel can reproduce to produce a breed known as c the cockapoo. The a African fish eagle is similar in appearance to the b bald eagle, but the two birds are members of different species. Fish and Wildlife Service. Speciation The biological definition of species, which works for sexually reproducing organisms, is a group of actually or potentially interbreeding individuals. The diagram shows similarities to phylogenetic charts that are drawn today to illustrate the relationships of species.

Allopatric Speciation A geographically continuous population has a gene pool that is relatively homogeneous. The northern spotted owl and the Mexican spotted owl inhabit geographically separate locations with different climates and ecosystems. The owl is an example of allopatric speciation. Adaptive Radiation In some cases, a population of one species disperses throughout an area, and each finds a distinct niche or isolated habitat.

The honeycreeper birds illustrate adaptive radiation. From one original species of bird, multiple others evolved, each with its own distinctive characteristics.

Link to Learning. Sympatric Speciation Can divergence occur if no physical barriers are in place to separate individuals who continue to live and reproduce in the same habitat? Art Connection. Aneuploidy results when the gametes have too many or too few chromosomes due to nondisjunction during meiosis. Autopolyploidy results when mitosis is not followed by cytokinesis. Alloploidy results when two species mate to produce viable offspring.

In the example shown, a normal gamete from one species fuses with a polyploidy gamete from another. Two matings are necessary to produce viable offspring. Reproductive Isolation Given enough time, the genetic and phenotypic divergence between populations will affect characters that influence reproduction: if individuals of the two populations were to be brought together, mating would be less likely, but if mating occurred, offspring would be non-viable or infertile.

These two related frog species exhibit temporal reproductive isolation. Speciation can occur when two populations occupy different habitats. The habitats need not be far apart. The cricket a Gryllus pennsylvanicus prefers sandy soil, and the cricket b Gryllus firmus prefers loamy soil. The two species can live in close proximity, but because of their different soil preferences, they became genetically isolated. The shape of the male reproductive organ varies among male damselfly species, and is only compatible with the female of that species.

Reproductive organ incompatibility keeps the species reproductively isolated. Some flowers have evolved to attract certain pollinators. The a wide foxglove flower is adapted for pollination by bees, while the b long, tube-shaped trumpet creeper flower is adapted for pollination by humming birds.

Habitat Influence on Speciation Sympatric speciation may also take place in ways other than polyploidy. Cichlid fish from Lake Apoyeque, Nicaragua, show evidence of sympatric speciation. Lake Apoyeque, a crater lake, is years old, but genetic evidence indicates that the lake was populated only years ago by a single population of cichlid fish. Nevertheless, two populations with distinct morphologies and diets now exist in the lake, and scientists believe these populations may be in an early stage of speciation.

Section Summary Speciation occurs along two main pathways: geographic separation allopatric speciation and through mechanisms that occur within a shared habitat sympatric speciation. Review Questions Which situation would most likely lead to allopatric speciation? A storm causes several large trees to fall down. A mutation causes a new trait to develop.

An injury causes an organism to seek out a new food source. What is the main difference between dispersal and vicariance? One leads to allopatric speciation, whereas the other leads to sympatric speciation. One involves the movement of the organism, and the other involves a change in the environment.

One depends on a genetic mutation occurring, and the other does not. One involves closely related organisms, and the other involves only individuals of the same species. What is the main difference between autopolyploid and allopolyploid? Which reproductive combination produces hybrids?

It does not share its habitat with related species. It does not exist out of a single habitat. It does not exchange genetic information with other species.