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Section 25_1: Identification of Species

Page history last edited by Teddy Kozlowski 10 years, 7 months ago

Grading Sheet (Teddy)


General Summary:

This chapter will examine how different species come into existence, we will talk about evolutionary changes that result in new species or a group that includes many species, a term known as macroevolution. There are various mechanisms that biologists use to determine what constitutes a new species. Scientists use specific criterion to divide populations into species, subspecies, or in the case of prokaryotes, ecotypes. Separating populations into distinct categories can sometimes be a difficult task, and often becomes arbitrary when analyzing a group of organisms that have minute differences in their characteristics. Being able to identify a species has multiple practical uses. It allows for scientists to create a preservation plan to protect an endangered species, and is important when a medical professional is trying to determine the bacterial species that is causing a certain disease, so he may prescribe the proper medication. Prezygotic barriers prevent the formation of a zygote by various mechanisms geared towards isolating distinct populations or ensuring that the egg is not fertilized. Postzygotic mechanisms allow for the formation of a zygote, but do not allow for development beyond the early stages of development. When two species do successfully interbreed, the offspring is known as an interspecies hybrid.


Detailed Summary:

The first part of this section talks about the process in which scientists determine how to classify populations.

In natural populations, it is sometimes difficult to determine what constitutes a new species. When two or more geographically restricted groups of the same species have only a few traits that differ, but is not enough to warrant placement into a new species, scientists classify such groups into a sub-species. When we apply this concept to bacterial species, they are known as ecotypes. An ecotype is a genetically distinct population that is adapted to its local environment. Each species is determined using characteristics and history that separates it from other species. When dealing with sexually reproducing organisms, it is common knowledge that members of different species usuallycan not successfully interbreed. Members of the same species also share a distinct evolutionary history, or ancestral lineage. The most commonly used characteristics to identify a species are morphological traits, ability to interbreed, molecular features, ecological factors, and evolutionary relationships. Morphological traits refers to an organisms obvious appearance. Molecular features are focused on comparing DNA sequences withing genes. This is accomplished by comparing gene placement on along chromosomes, chromosome structure, and chromosome number. Ecological factors uses factors of an organisms habitat to distinguish one species from another. For example, whether an organism searches for food on the ground or primarily in small trees can be indicative of a separate species. This method is especially helpful for distinguishing bacterial species, as members of the same species are likely to use the same type of resources. Evolutionary relationships are based on an analysis of a fossil record and DNA sequences. This method is often useful when attempting to construct evolutionary trees that will explain the relationship between ancestral species and modern species.


Reproductive Isolation is a term meaning that two organisms of different species are unable to reproduce with one another to form a viable and fertile offspring. In the 1920's, the idea that each species is reproductively isolated from other species was proposed by Theodosius Dobzhansky. This method is commonly used to differentiate plants and animal species that are metamorphically similar, but can not interbreed.


The species concept is a way to define the concept of a species and/or provide an approach to distinguish one species from another.  The biological species concept states that a species is a group of individuals whose members have the ability to interbreed with one another to produce a viable and fertile offspring, but can not successfully interbreed with members of a different species. This idea emphasizes reproductive isolation as the primary criterion for determining a species. The ecological species concept proposes that each species occupies an ecological niche, which is the unique set of habitat resources that a species requires, as well as its' influence on the environment and other species. This concept depicts the characterization of ecological factors to determine a species with emphasis on the ideal environment for an organism to survive in.


Reproductive Isolating Mechanisms are the mechanisms that prevent interbreeding between different species. This can be accomplished in two general ways. Prezygotic Isolating Mechanisms prevent the formation of a zygote. These include habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, and gametic isolation.  Mechanical Isolation and Gametic isolation are examples of attempted but failed mating attempts. Postzygotic Isolating Mechanisms allow for fertilization of the egg, but block the development of a viable and fertile offspring beyond that point. These methods include hybrid inviability, hybrid sterility, and hybrid break down. All have which been discussed in detail.





Species: A group of related organisms that maintains a distinctive set of attributes in nature 

Speciation: The formation of new species through the divergence of an ancestral species

Subspecies:When two or more geographically restricted groups of the same species display one or more traits that are somewhat different but not enough to warrant their placement into different species.

Ecotype: (Pertaining to subdivision of bacterial cells) A genetically distinct population adapted to its local environment.

Reproductive Isolation: Prevents one species from successfully interbreeding with another species.

Species Concept: A way to define the concept of a species and/or provide an approach to distinguish one species from another.

Lineage:A series of species that forms a line of descent, with each new species the direct result of speciation from an immediate ancestral species

Reproductive Isolating Mechanisms: Mechanisms that prevent interbreeding between different species


Useful Materials:


This Website Provides an excellent overview on a wide array of topics covered in this section. When you first enter this page, you will find yourself at the Biological Species Concept. It explains this concept further, and how morphological appearances are not always the determining factor when deciding how to group an organisms into a species. It continues on the same page to talk about how separating organisms into species can sometimes be a very difficult and almost arbitrary task. I especially like this page because it further explains examples from our books while also including their own unique animated situations.


This website also include information on other species concepts that have not been covered in this section. For those who are having trouble with the concept of speciation, this website has an entire page dedicated to fun animations that will help you understand. The website continues on to talk about the concept of macroevolution and what it really means. It is an easy and fun read that will definitely be beneficial if you are struggling with some of the main ideas or just want to have a better understanding of the topic.


This is another website from a top state university. I find it to be very informative when dealing with reproductive isolating mechanisms. This page breaks down each isolating method and gives examples using pictures as well as an explanation to go along with it. It also links to two different pages that provide additional examples and explanations of interspecies hybrid.


The links that they provide are helpful when trying to understand why an interspecies hybrid is sterile. It explains the affect that the uneven number of chromosomes inherited can have on an organism. The original webpage also talks about species reinforcement. Species reinforcement will most probably be a topic talked about during our class discussion on Friday. So I would strongly advise you to read up on it and look for other websites that explain the information further.


The abstract of this article alone is a great tool for understanding some of the species concepts. This article focuses on genetic isolation rather than reproductive isolation as the method that separates two species. The Genetic Isolation Concept is different from the Biological Species Concept. The GSC focus on genetic isolation where as BSC focuses on the fact that members of different species are reproductively isolated from  one another.


A lot of this article is extracurricular reading, but I am sure many of you will find it interesting. The GSC uses genetic information from both the mitochondria and nucleus as a way to determine where to draw the line between species. "The definition of the GSC is more compatible with a description of biodiversity in mammals rather than is reproductively isolated species".



This is a funny video that ties together and further explains prezygotic and postzygotic barriers. It is helpful in understanding these isolation mechanisms as sometimes just reading text is not enough of an explanation. It is a humorous video, and sometimes when someone explains something in a unique way it can make it much easier to remember. Therefore, I think everyone should watch this quick video.


Primary Literature:





This link brings you to a database that talks more about how the 16s rRNA gene plays an important role when trying to classify different strains of bacteria. It begins by talking about how other mechanisms used in the past to distinguish different strains of bacteria are inefficient when trying to identify a large number of species. The paper also includes detailed charts that visually explain their results.


It discusses how this gene sequence came to be particularly important when classifying bacteria. The results from the study proved that 5' end of the gene was the Hyper Variant region, and that each of these regions were genetically distinct when comparing the members of one species to another species. This proved a useful way of classifying different strains, especially since each HV region was conserved withing the species.


Creating a database of the sequence has been more of a break through than it may appear. In our lectures, we discussed the many complications that come along with classifying an organism into a species. Often times, it is arbitrary how we decide to group different organisms or populations. Classification becomes especially difficult when dealing with bacteria, a microorganism that participates in Horizontal Gene Transfer. There are such minute differences that it becomes hard to decide where to draw the line. Sequencing this gene gave biologist a way to group organisms into their correct species. If the gene sequence of the 16s rRNA gene of two populations are very similar, they are likely to be grouped into the same species. Where as if two populations have gene sequences that vary greatly, it may warrant placement into their own distinct species.








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