Main Difference – Anagenesis vs Cladogenesis
Anagenesis and cladogenesis are two types of evolutionary mechanisms. Both anagenesis and cladogenesis lead to speciation. Anagenesis is the transformation of a particular lineage of organisms to a different state, which can be justified as a new species from its ancestral species. Cladogenesis is the splitting of an ancestral species into several, new species. The main difference between anagenesis and cladogenesis is that anagenesis is a type of phyletic evolution, which occurs only within a single species whereas cladogenesis is a type of branching evolution. In other words, in anagenesis, one gene pool is converted into another gene pool. In contrast, in cladogenesis, a single gene pool is split into several gene pools.
Key Areas Covered
1. What is Anagenesis
– Definition, Characteristics, Role
2. What is Cladogenesis
– Definition, Characteristics, Role
3. What are the Similarities Between Anagenesis and Cladogenesis
– Outline of Common Features
4. What is the Difference Between Anagenesis and Cladogenesis
– Comparison of Key Differences
Key Terms: Adaptations, Anagenesis, Cladogenesis, Evolution, Natural Selection, Phyletic Evolution, Speciation
What is Anagenesis
Anagenesis is an evolutionary change of a single lineage where one taxon is replaced by another without branching. Anagenesis is called phyletic evolution or progressive evolution. Anagenesis occurs due to the specialization of individuals in a particular species in response to stimuli of the external environment. Natural selection promotes the adaptations of the individuals in relation to the existing conditions. The increase of the complexity and the perfection of the adaptations is a biological process, which occurs continuously, promoting a particular species to a higher level.
Characteristics of Anagenesis
- The increased complexity and the rationalization of organs to improve the function
- The division of labour in body parts
- The increased complexity of the central nervous system
- The increased resistance to the changes in the external environment
Anagenesis degenerates the unnecessary organs in parasites, increasing the parasitic nature. The serially-repeated body parts of organisms such as arthropods and crustaceans show a high tendency towards specialization via anagenesis. The segmental ganglia are centralized in the brain during anagenesis. It was anagenesis that resulted in the increased complexity and rationalisation of the brain in ape-like ancestors.
Figure 1: Increased Length of the Neck in Giraffe
Three types of anagenesis can be identified based on the speed of the process; tachytely, horotely, and bradytely. The very rapid anagenesis is called the tachytely. The moderate anagenesis is called the horotely while the very slow anagenesis is called the bradytely. The bradytely occurs in stable environments. The increased length of the neck in giraffe is an example of anagenesis.
What is Cladogenesis
Cladogenesis is an evolutionary change of a particular species in which new species are branched off from a common ancestral species. Cladogenesis is the most common mode of speciation in response to the changes in the conditions of the environment. Since more than one species are produced from a single species during cladogenesis, cladogenesis brings biological diversity to the environment. Therefore, cladogenesis is an active evolutionary process than anagenesis. Cladogenesis is also called the branching evolution. Both anagenesis and cladogenesis are shown in figure 2.
Figure 2: Anagenesis vs Cladogenesis
The three types of cladogenesis classified based on the speed of the process are tachyschizia, horoschizia, and bradyschizia. The tachyschizia is the rapid splitting of lineages, which occurs due to their invasion of a new habitat or due to the extinction of competitors. When new opportunities are available for the population to increase their number in a particular habitat, they rapidly diversify to adapt to that environment. In horoschizia, cladogenesis occurs at a moderate rate when the environmental conditions are not very harsh. The bradyschizia occurs very slowly.
Similarities Between Anagenesis and Cladogenesis
- Both anagenesis and cladogenesis are types of evolutionary mechanisms.
- Both anagenesis and cladogenesis occur in response to the changes in the environment.
- Both anagenesis and cladogenesis lead to the speciation.
- Both anageneis and cladogenesis ca be categorized based on the speed of occurrence of each process.
Difference Between Anagenesis and Cladogenesis
Definition
Anagenesis: Anagenesis is an evolutionary change of a single lineage in which one taxon replaces by another without branching.
Cladogenesis: Cladogenesis is an evolutionary change of a particular species in which new species are branched off from a common ancestral species.
Branching
Anagenesis: No branching of the lineage occurs in the anagenesis.
Cladogenesis: The branching of the lineage occurs in the cladogenesis.
Type of Evolution
Anagenesis: Anagenesis is an evolution within a lineage.
Cladogenesis: Cladogenesis is an evolution which results in the splitting of a lineage.
Alternative Name
Anagenesis: Anagenesis is called the phyletic evolution or the progressive evolution.
Cladogenesis: Cladogenesis is called the branching evolution.
Gene Pool
Anagenesis: In anagenesis, one gene pool is converted into another gene pool.
Cladogenesis: In cladogenesis, a single gene pool is split into several gene pools.
Biological Diversity
Anagenesis: Anagenesis does not promote biological diversity.
Cladogenesis: Cladogenesis promotes biological diversity since it increases the number of species.
Types
Anagenesis: The three modes of the anagenesis are tachytely, horotely, and bradytely.
Cladogenesis: The three modes of the cladogenesis are tachyschizia, horoschizia, and bradyschizia.
Conclusion
Anagenesis and cladogenesis are two evolutionary processes, which occur in response to the changes in the environmental conditions. Both anagenesis and cladogenesis lead to speciation. Anagenesis occurs in a single lineage. In cladogenesis, several distinct species occur from a single species. The main difference between anagenesis and cladogenesis is the mechanism of each type of the evolutionary process.
References:
1.“Anagenesis & Cladogenesis .” IASZoology.com, Available here. Accessed 2 Oct. 2017
Image Courtesy:
1. “Dibujo explicativo” By Sandritaverooka – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Speciation cladogram subtype” By Faustino Núñez Hernández – Own work (CC BY-SA 3.0) via Commons Wikimedia
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