The potential connection (phylogenetic relationship) between several groups of species is graphically represented by a cladogram. It is used in phylogenetic analysis to ascertain the evolutionary link between species.
The Greek terms clados and gramma, which indicate branch and characters respectively, are whence the word cladogram gets its name. It is a depiction of a phylogenetic study that is not scaled and in which only the topography of the diagram is significant. It is a straightforward diagram that summarises a pattern of traits across several creatures, but it lacks a time axis. Although a cladogram involves fictitious ancestors to determine a link, it serves as the basis for more investigation.
Features of a cladogram
- The cladistic approach produces trees, which are relative assertions of kinship rather than indications of ancestors or descendants. For instance, it suggests that mammals and birds are linked, although neither mammals nor birds are thought to have evolved from one another.
- A cladogram’s branch lengths have no phylogenetic significance, since they are not proportionate to the number of evolutionary changes.
- A cladogram’s external taxa are arranged neatly in a row or column.
- Cladograms are created by analysing DNA or RNA sequencing data and the morphological characteristics of the species. Recently, however, the merging of the already-existing features for the creation of cladograms has also included computational phylogenetics.
- The presumptions used to create phylogenetic trees are called cladograms.
- Cladograms come in a variety of designs, but they always include lines that diverge from other lines to depict the alleged ancestors of various creatures.
Parts of a cladogram
A cladogram is a diagram made up of the sections listed below:
- The earliest common ancestors of any and all organisms in a cladogram are referred to as their roots.
- Every cladogram has a root that serves as its origin. The root, however, could also suggest that it originates from some other, more substantial clades.
- Every node represents a hypothetical progenitor that gave rise to at least two daughter taxa.
- Nodes in all cladograms reflect the branching point of divergence.
- As a result, there is a node at each location where a group of organisms splits or separates into other groups.
- Clades are groups of organisms or genes that contain both the latest common ancestor of their members and their offspring.
- An ancestor and all of its offspring constitute a clade.
- It contains a specific node and every branch that connects to it.
Taxon / Outgroup
- Taxon or outgroup refers to the most distantly connected species of animal that is not usually a clade.
- This serves as a benchmark or point of comparison for the other nodes in the cladogram.
- A cladogram’s branches are the lines that link each of the other elements.
- In certain instances, the branch length reflects the degree of divergence or the degree of connection between several species.
How to make a cladogram (Building cladograms)
- As previously mentioned, cladograms may be produced using either morphological traits or molecular data such as DNA, RNA, or protein sequencing.
- Consequently, they may be created in one of two ways based on the characters used in the cladograms:
1. Using structural and morphological characteristics
Step 1. Determine the specified characters that will be utilised
- The first phase in phylogenetic analysis is to determine if a trait is evolved or primitive (innate).
- In this situation, it is best to choose characters who are not affected by their surroundings.
- The main technique for creating cladograms or other types of trees is the outgroup comparison approach.
- As in outgroup technique, a feature about an organism is selected when the creature is not a member of the family of animals must be classified but the trait is shared by a few of the group’s organisms. This characteristic may then be used as a specified character.
- The organisms being classed are the ingroup in this instance, while the external organism is referred to as the outgroup.
- Other traits are now chosen from the group to further divide the organisms in the ingroup.
|Two pairs of limbs||X||X||X|
- In this case, the outgroup is represented by the creature with the fewest traits in common. Shark is the outgroup in the table above.
Step 2: Arrange the creatures into groups based on their similarities.
- A Venn diagram for the grouping of the creatures may be created before creating a cladogram.
- Begin by putting the character present in every category on the outside of the Venn diagram.
- Next, create a cladogram from the Venn diagram.
B, Using molecular characters
Step 1: Selection of the molecular evidence common among the selected organisms
- The initial stage in phylogenetic synthesis with molecular data is deciding whether to utilise DNA or protein sequences.
- In most situations, protein sequences are preferred.
- However, DNA is the preferred marker for research on recent evolution.
- Two instances of proteins that are found in several different kinds of animals are haemoglobin and cytochrome c.
Step 2: Collect and run the multiple sequence alignment to compare the molecular sequences (DNA or amino acid) for each of the organisms selected.
- Software for multiple sequence alignment, such as Clustal Omega, may be used to compare and contrast various DNA or amino acid sequences.
- In comparison to creatures that are distantly linked, closely related organisms will have more sequence similarities.
Step 3: Generate a cladogram from the obtained data of the multiple sequence alignment
- The next step is to choose a suitable replacement model that incorporates the outcomes of multiple sequence alignment to produce estimates of the link between the organisms.
- The Jukes-Cantor and Kimura models of nucleotide substitution are often used.
- The PAM and JTT models are the two most commonly used models for amino acid replacement.
How to read a cladogram? (Interpreting cladograms)
- Even though a cladogram just offers a rough outline of how various creatures are related to one another, it nonetheless helps identify relationships.
- Let’s take the following cladogram example into consideration for its interpretation.
- The cladogram above examines four phylogenetic traits.
- This indicates that kangaroos and people are more closely connected than bullfrogs and people.
- This cladogram is not scaled, therefore it cannot be used to gauge the size of the connection.
- Both the direction of the lines and the arrangement of the animals are irrelevant.
- Similar to the cladogram, the relationships between the creatures decrease as we travel to the right of the picture. More distantly related to humans than bulldogs are sharks.
- All cladograms are hypothetical, hence they do not list the potential ancestors of the creatures.
- The shark is the outgroup in the figure above, while the human and kangaroo constitute a clade.
Different styles of cladograms
- Depending on the branch shapes and branch orientations, there are several cladogram styles.
- The size, length, and orientation of the branches are unimportant since a cladogram is an unscaled depiction of a phylogenetic study.
- Here are some examples of cladogram drafting techniques:
- Two phylogenetic features that show the same connection between the three creatures are examined in both of the provided figures.
- Cladograms may be used to distinguish between several creatures based on certain particular common traits.
- Examples of cladograms that may be used to separate species into several groups according to their morphological characteristics include the following:
Cladogram of primates
- Based on a few distinctive characteristics, primates may be divided into several taxa.
- Lemurs and lorises are regarded as the outgroup in the cladogram above, whereas the remainder are thought to be in the ingroup.
- The clade that includes lemurs and lorises also has a common node.
- The interior nodes of the cladogram represent fictitious ancestors of various groupings.
- The groupings are also more closely connected to one another the closer they are to one another.
Cladogram of vertebrates
- Vertebrates may also be further classified into groups according to a variety of traits.
- The cladogram shown above illustrates how vertebrates vary from one another depending on their ventrolateral muscle layers.
- Each group in the cladogram has at least two muscle layers in common.
- As we climb higher towards the top, the taxa are divided according to whether the ventrolateral body wall has four layers or not.
- The bony fish constitute the outgroup in this situation, whereas the other species are included in the ingroup.
- Crocodiles and birds also share a common ancestor and belong to the same clade.
- Like in all previous cladograms, the closer the creatures are to one another in the cladogram, the more similar to one another they are morphologically.
Cladogram vs. Phylogenetic tree (Phylogram)
- The diagrammatic depiction of phylogenetic analysis includes both the cladogram and the phylogenetic tree.
- These two provide a connection between various assemblages of creatures.
- Both the cladogram and the phylogenetic tree employ the same characteristics, which are constructed in a similar manner.
- However, the cladogram is often regarded as the first stage in the creation of a phylogenetic tree.
Differences between a cladogram and phylogenetic tree (phylogram)
|Characteristics||Cladogram||Phylogenetic tree (phylogram)|
|Nature||Cladograms are mostly simple and can be used for the general classification of organisms.||Phylogenetic trees are more complex and are mostly used to determine the evolutionary relationship between different groups of organisms.|
|Representation||Cladograms do not represent the evolutionary relationships between different groups of the organism and thus is not an evolutionary tree.||A phylogenetic tree is an evolutionary tree that shows the evolutionary relationships between different groups of animals.|
|Use||Cladograms give a hypothetical picture of the actual evolutionary history of the organisms.||Phylogenetic trees give an actual representation of the evolutionary history of the organisms.|
|Length of the branches||All the branches in a cladogram are of equal length as they do not represent any evolutionary distance between different groups.||The branches in a phylogenetic tree usually are of different lengths as they represent the evolutionary distance between the groups.|
|Evolutionary time||The separation of the organism in a cladogram is solely based on the defined characters. Thus, the distance doesn’t indicate the evolutionary time of the groups.||A phylogenetic tree indicates the duration of evolution and the relative divergence time of the branches based on the distance between the groups.|
|Position of external taxa||The external taxa of a cladogram line up neatly in a row or a column.||The external taxa of a phylogenetic tree might or might not line up in a row or a column.|
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