What is the Difference Between Dichotomous Key and Phylogenetic Tree

The main difference between dichotomous key and phylogenetic tree is that dichotomous key guides towards the final identification of an organism through several steps with two statements which describe certain characteristics whereas phylogenetic tree describes the evolutionary path organisms follow to become unique species, starting with a common ancestor. Furthermore, the leads of the dichotomous key always represent many organisms, while each branching point represents an individual organism in the phylogenetic tree. 

Dichotomous key and phylogenetic tree are two types of diagrams which represent a group of organisms. Generally, both of them provide relationships between organisms in the group. 

Key Areas Covered 

1. What is Dichotomous Key
     – Definition, Features, Importance
2. What is a Phylogenetic Tree
     – Definition, Features, Importance
3. What are the Similarities Between Dichotomous Key and Phylogenetic Tree
     – Outline of Common Features
4. What is the Difference Between Dichotomous Key and Phylogenetic Tree
     – Comparison of Key Differences

Key Terms 

Common Ancestor, Couplet, Dichotomous Key, Lead, Leaf, Node, Phylogenetic Tree

What is Dichotomous Key 

A dichotomous key is a diagram which allows the identification of a group of organisms by dividing them into two categories repeatedly. These categories are called ‘leads’ while a set of leads at a given point is called a ‘couplet’. When an organism no longer shares its selected characteristics with any other organism, it has been identified. However, the above-selected characteristics have to be immutable, or in other words, they do not change. As examples, coloration, size, and behavioral features may vary among individuals as well as throughout their lifetime. However, physical structures such as the number of limbs and biochemical processes such as reproduction methods are better characteristics.

Figure 1: Dichotomous Tree of Extant Shark Orders

Furthermore, two types of dichotomous keys are there based on the method of representation. They are the diagrammatic representation as a branching flowchart and descriptive representation as a series of paired statements laid out in numbers. However, the dichotomous key does not provide any kind of trustworthy phylogenetic relationships of organisms in the diagram. 

What is Phylogenetic Tree 

A phylogenetic tree is a diagram that represents the evolutionary pathway of closely-related organisms descended from a common ancestor. Generally, it depends on the similarities and differences in the physical and genetic characteristics. Significantly, the descending points from the common ancestor are shown by nodes while leaves represent each entity. Furthermore, there are two main types of phylogenetic trees. They are rooted and unrooted phylogenetic trees. 

Figure 2: Phylogenetic Tree

Moreover, in the rooted phylogenetic tree, each node with descendants represents the most common ancestor. Also, it is a taxonomic unit. In addition to these, the edge length of some trees interprets the time taken for evolution. However, unrooted trees only interpret the relatedness of a group of organisms. But, they do not make assumptions about ancestry. 

Similarities Between Dichotomous Key and Phylogenetic Tree  

• Dichotomous key and phylogenetic tree are two types of branching diagrams, representing a group of closely-related organisms.  
• Both allow character-based identification of organisms. 

Difference Between Dichotomous Key and Phylogenetic Tree 

Definition 

Dichotomous key refers to a diagram constructed using contrasting characteristics to divide the organisms in the key into smaller and smaller groups while phylogenetic tree refers to a diagram showing the evolutionary relationships among various biological species. 

Purpose 

The main purpose of the dichotomous key is to identify individuals while the main purpose of the phylogenetic tree is to describe the evolutionary relationships of organisms to their common ancestor. 

Significance 

The dichotomous key contains several steps with two statements which describe certain characteristics while the phylogenetic tree contains several steps, which shows the degree of divergence of an organism from its common ancestor. 

Components 

The dichotomous key contains alternatives called “leads” and the set of leads at a given point called a “couplet” while phylogenetic tree contains leaves and nodes. 

Representation 

Many leads of the dichotomous key represent a group of organisms with similar characteristics while each branching point represents an individual organism in the phylogenetic tree. 

Conclusion 

A dichotomous key is a diagram which helps to identify each individual in a group of organisms through a selection process of two statements. It also consists of leads and couplets. In contrast, a phylogenetic tree is a diagram, which helps to describe the evolutionary relationships of a group of related organisms. However, it consists of leaves and nodes. Therefore, the main difference between the dichotomous key and phylogenetic tree is the purpose of the diagram. 

References:

1. Cornell, Brent. “Dichotomous Keys.” BioNinja, Available Here.
2. “Phylogenetic Trees.” Khan Academy, Khan Academy, Available Here.

Image Courtesy:

1. “Extant Shark Orders (illustrated)” By Chris huh (Public Domain) via Commons Wikimedia   
2. “Phylogenetic tree” By This vector version: Eric Gaba (Sting – fr:Sting) – NASA Astrobiology Institute, found in an article (Public Domain) via Commons Wikimedia