Thursday, April 18, 2024

What Is The Biological Species Concept

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Genetic Similarity And Barcode Species

The Biological Species Concept

In microbiology, genes can move freely even between distantly related bacteria, possibly extending to the whole bacterial domain. As a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%.

DNA-DNA hybridisation is outdated, and results have sometimes led to misleading conclusions about species, as with the pomarine and great skua. Modern approaches compare sequence similarity using computational methods.

DNA barcoding has been proposed as a way to distinguish species suitable even for non-specialists to use. The so-called barcode is a region of mitochondrial DNA within the gene for cytochrome c oxidase. A database, Barcode of Life Data Systems , contains DNA barcode sequences from over 190,000 species. However, scientists such as Rob DeSalle have expressed concern that classical taxonomy and DNA barcoding, which they consider a misnomer, need to be reconciled, as they delimit species differently. Genetic introgression mediated by endosymbionts and other vectors can further make barcodes ineffective in the identification of species.

Species Concepts In Phytoplankton

The species concept for most phycologists is based on the morphological characters and hence the term species means morphospecies. On the other hand, for evolutionary biologists the term means biological species that can be defined as a reproductive community of populations that occupy a specific niche in Nature. If we accept the above definition of species, any talk about biological species in groups where sexual reproduction has not been observed yet is meaningless. Nevertheless, recent concepts argue that it would be unproductive and inconvenient to restrict the term species exclusively to one or the other.

James H. Thorp, … Walter W. Dimmick, in, 2015

Iib4phylogenetic Evolutionary And Genealogical Species Concepts

Other more recently derived species concepts rely more heavily on a retrospective view by defining a species in a strictly historical sense as a separate evolutionary lineage that is internally connected through time , the evolutionary species concept , and the genealogical species concept for a good overview, see Harrison article in Howard and Berlocher, 1998). These species concepts are less oriented toward process and identifying specific biological traits that maintain cohesion within species or promote divergence between species and instead are more oriented toward the final evolutionary resultlineage divergence. That is not to say that process cannot be usefully inferred from looking at historical patterns of lineage sorting and splitting , but the emphasis in these particular species concepts is clearly on pattern rather than on trying to incorporate a variety of biological processes into the species definitions themselves.

Hope Hollocher, in, 2013

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How Can We Look At Speciation In Action

We can study the process of speciation in the natural world without focussing on the reproductive isolation element of species identity as well. For many species, we are unlikely to have the detail required to study speciation at this level in any case. Instead, we might choose to focus on the different factors that are currently influencing the process of speciation, such as how the environmental, demographic or adaptive contexts of populations plays a role in the formation of new species. Many of these questions fall within the domain of phylogeography particularly, how the historical environment has shaped the diversity of populations and species today.

A variety of different analytical techniques can be used to build a picture of the speciation process for closely related or incipient species. A good starting point for any speciation study is to look at how the different study populations are adapting is there evidence that natural selection is pushing these populations towards different genotypes or ecological niches? If so, then this might be a precursor for speciation, and we can build on this inference with other complementary analyses.

Species Delimitation Based On Interfertillity


To construct the mating network for the adult trees, we made use of a progeny test involving 3046 offspring resulting from open pollination, harvested from 51 mother-trees distributed across the entire stand . A paternity analysis was conducted by genotyping all the offspring from the test and all the adults trees for which DNA was available, using 12 multiplexed microsatellite markers developed by Guichoux et al. . According to the paternity analysis, 1575 offspring had only one possible father in the stand, 54 offspring had several potential fathers in the stand and 1417 offspring had no father in the stand . Based on the offspring for which only a single father was found, we identified 198 father-trees in the stand. These trees included 43 trees that were also mothers, because oak trees are monoecious. Based on these results, we reconstructed 1629 mating events between 206 adult trees within the stand. These mating events allowed us to identify 751 couples of trees that mated at least once, indicating that they were interfertile under natural conditions. These data were represented by an undirected and unweighted network in which each of the 206 nodes corresponded to an adult tree and each of the 751 links corresponded to at least one mating event between two trees.

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Speciation Is A Process

Speciation, or the process that results in new species, occurs when an ancestral population splits into two or more descendant species which are genetically distinct and unable to interbreed . Speciation is all about gene flow or lack thereof. The less gene flow, the more likely speciation is to occur. There are two different mechanisms of speciation, based on the mechanism that prevents gene flow: allopatric speciation and sympatric speciation.Allopatric speciation can occur when two populations are physically isolated from each other , creating the absence of gene flow. In the figure below, geographic isolation occurs when a beetle population is divided by a body of water that prevents interbreeding between the two populations. Small changes occur in each isolated population over time, and if changes occur that prevent successful production of fertile offspring, then when the isolating barrier is removed, the two populations can no longer interbreed.

What was once a continuous population is divided into two or more smaller populations. 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

Post-zygotic reproductive isolation can include:

Reproductive Isolation Through Dmis

The reproductive incompatibility of two populations is often intrinsically linked to the genetic make-up of those two species. Some conflicts in the genetics of Population 1 and Population 2 may mean that a hybrid having half Population 1 genes and half Population 2 genes will have serious fitness problems . Dramatic genetic differences, particularly a difference in the number of chromosomes between the two sources, is a significant component of reproductive isolation and is usually to blame for sterile hybrids such as ligers, zorse and mules.

However, subtler genetic differences can also have a strong effect: for example, the unique combination of Population 1 and Population 2 genes within a hybrid might interact with one another negatively and cause serious detrimental effects. These are referred to as Dobzhansky-Müller Incompatibilities and are expected to accumulate as the two populations become more genetically differentiated from one another. This can be a little complicated to imagine , but the basis of the concept is that some combinations of gene variants have never, over evolutionary history, been tested together as the two populations diverge. Hybridisation of these two populations suddenly makes brand new combinations of genes, some of which may be have profound physiological impacts .

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Explains The Importance Of Reproduction In The Perpetuation Of Species

For species to continue to survive, they need to undergo reproduction. And that is what the biological species concept is mainly about: reproduction. According to the concept, individuals continually look for other individuals as potential partners in order to continue the existence of their species.

The Future Of Speciation Genomics


Although these can help answer some questions related to speciation, new tools are constantly needed to provide a clearer picture of the process. Understanding how and why new species are formed is a critical aspect of understanding the worlds biodiversity. How can we predict if a population will speciate at some point? What environmental factors are most important for driving the formation of new species? How stable are species identities, really? These questions remain elusive for a wide variety of life on Earth.

This is Part 1 of a four part miniseries on the process of speciation how we get new species, how we can see this in action, and the end results of the process. This week, well start with a seemingly obvious question: what is a species?

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The Sex And Gender Arguments

The most commonly used argument against alternative concepts of either gender of sex the binary states of a man with a male body and a female with a female body is often based on some perception of biologically reality. As a biologist, let me make this apparently clear that such confidence and clarity of reality in many, if not all, biological subdisciplines is absurd . Biologists commonly acknowledge the realisation that life in all of its constructs is unfathomably diverse, unique, and often difficult to categorise. Any impression of being able to do so is a part of the human limitation to process concepts without boundaries.

The Biological Species Concept

By far the most well-known species concept is the biological species concept, which was proposed by evolutionary biologist Ernst Mayr. The biological species concept states that a species is a group of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups. Reproductive isolation can occur in several ways individuals of different groups may not mate with each other, their mating may not produce offspring, or the offspring produced may not be viable or fertile .

In some cases, the biological species concept is straightforward and easy to apply. For instance, the western meadowlark and the eastern meadowlark , both shown in Figure 1, respectively inhabit the western and eastern halves of North America. Despite the fact that their breeding ranges overlap throughout many upper midwestern states, including Michigan, Wisconsin, Illinois, Iowa, Missouri and Minnesota, the two groups do not interbreed. The courtship songs of the males of each species are distinctly different and females of each species respond to the songs of the males of their own species, leading to strong reproductive isolation between the two groups despite a high degree of similarity in appearance.

Figure \:Males of the western meadowlark, Sturnella neglecta and the eastern meadowlark Sturnella magna .Images from Wikimedia Commons1,2

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Species Delimitation Based On Multilocus Genotypes

Guichoux et al. used genotypic similarity as a criterion to assign the trees of the study site to species. These authors genotyped the adult trees with the multiplex of 12 SSRs developed by Guichoux et al. and with a chip of 262 single-nucleotide polymorphisms enriched with markers highly differentiated between species . They used the software structure to group the individuals into genotypic clusters but did not formally determine the optimal number of genotypic clusters in the stand before performing the clustering. Here we used the K statistic to identify the number of genetically different groups. The optimal number of clusters was two , as previously assumed by Guichoux et al. . The adult trees were therefore classified in two purebred groups and one genetically intermediate class. Among the 206 adult trees included in the mating and relatedness networks, 78 trees were assigned to the first purebred group , 118 to the second purebred group and 10 to the genetically intermediate class .

Why Do We Need To Identify Organisms

Ecological Species Concept

In microbial ecology, the identification of microorganisms helps us characterize biodiversity. Because the clinical samples will most likely contain many microorganisms, both normal flora and pathogens, it is important to isolate the pathogen in a pure culture using various types of selective and differential media.

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What Are 4 Ways A New Species Can Develop

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.

Is Reproductive Isolation Naturally Selected For Or Just A Consequence

A fundamental aspect of studies of speciation is a chicken or the egg-type paradigm: does natural selection directly select for rapid reproductive isolation, preventing interbreeding or as a secondary consequence of general adaptive differences, over a long history of evolution? This might be a confusing distinction, so well dive into it a little more.

Of the two proposed models of speciation, the by-product of natural selection has been the more favoured. Simply put, this expands on Darwins theory of evolution that describes two populations of a single species evolving independently of one another. As these become more and more different, both in physical and genetic characteristics, there comes a turning point where they are so different that an individual from one population could not reasonably breed with an individual from the other to form a fertile offspring. This could be due to genetic incompatibilities #Mechanisms_of_reproductive_isolation” rel=”nofollow”> different chromosome numbers), physiological differences , or behavioural conflicts .

A) B)C)D) E)

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C Tends To Ignore Hybridization

This phenomenon occurs when there is a mating between two genetically distinct species that creates a new organism.

  • The offspring, often infertile , then has inherited the characteristics of both of its parents.
  • Example: A hybrid between a horse and a donkey a mule. Basically, these infertile species are incapable of mating with either of the parent species. And as alluded earlier in the previous items, the definition of a species based on the concept is invalid and inapplicable to this phenomenon.

Mayr’s Biological Species Concept

Biological Species Concept

Ernst Mayr‘s 1942 book was a turning point for the species problem. In it, he wrote about how different investigators approach species identification, and he characterized their approaches as species concepts. He argued for what came to be called the Biological Species Concept , that a species consists of populations of organisms that can reproduce with one another and that are reproductively isolated from other populations, though he was not the first to define “species” on the basis of reproductive compatibility. For example, Mayr discusses how Buffon proposed this kind of definition of “species” in 1753.Theodosius Dobzhansky was a contemporary of Mayr and the author of a classic book about the evolutionary origins of reproductive barriers between species, published a few years before Mayr’s. Many biologists credit Dobzhansky and Mayr jointly for emphasizing reproductive isolation.

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Species Delimitation Based On Morphology

The morphological similarity criterion has previously been used by Bacilieri et al. to identify all trees from the study site. These authors performed a factorial discriminant analysis based on 31 leaf morphological traits to delimit the species. Their study revealed the presence of two groups of individuals differing in their morphology. The first axis of the FDA accounted for 33% of the total variance and was highly correlated to the morphological markers traditionally used by taxonomists to distinguish Q. robur from Q. petraea. The distribution of the individuals along this axis was used to assign, graphically, the individuals to two pure morphological groups and to a morphologically intermediate class . Among the 206 adult trees included in the mating and relatedness networks, 123 trees were assigned to M1, 80 to M2 and 3 to Mi .

Phylogenetic Or Cladistic Species

Unlike the biological species concept, a cladistic species does not rely on reproductive isolation â its criteria are independent of processes that are integral in other concepts. Therefore, it applies to asexual lineages. However, it does not always provide clear cut and intuitively satisfying boundaries between taxa, and may require multiple sources of evidence, such as more than one polymorphic locus, to give plausible results.

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What Is A Biological Species Concept

The Biological Species Concept defines a species taxon as a group of organisms that can successfully interbreed and produce fertile offspring. According to that concept, a species‘ integrity is maintained by interbreeding within a species as well as by reproductive barriers between organisms in different species.

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B Does Not Take Into Consideration The Changes That Happen Over Time

  • The very concept seems to be widely problematic especially when applied to the field of paleontology.
  • Paleontologists study organisms that are separated by thousands of years hence it would be difficult to determine whether such organisms were once part of the same reproductive community.
  • Example: In case of the dinosaurs, since no more species of dinosaurs are existing at present, it would be absolutely impossible to trace their mating pattern or part in the reproductive community. Hence, field of paleontology requires a different concept to define a species

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D Has Problems Regarding Classifying Non

In the kingdoms of biological organisms, it is apparent that some organisms are classified as neither males nor females.

  • Several modes of uni-parental births have already been recorded and such have been geared of evolutionary significance. The definition of a species according to the biological species concept tends to be inapplicable in many cases in the biological world.
  • Example: Many species of bacteria reproduce through asexual process and are assigned to each species based on their chemical and structural characteristics. Again, the Biological Species concept requires organisms to mate with each other and exchange their genetic material in order to be called a species.
  • Bacteria deviate from this definition, hence, other species concept should be used.

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