Speciation

Unit : Natural selection

Chapter: Speciation

Reference: Speciation, Speciation Causes, Natural selection

Genetic drift, Migration, Natural causes, Types of speciation, Allopatric Speciation, Example of allopatric speciation, Sympatric Speciation, Examples of sympatric speciation

 

Learning objectives

  • To describe the conditions under which new species may arise.
  • To describe the rate of evolution and speciation under different ecological conditions.
  • To explain the processes and mechanisms that drive speciation.
  •  

Speciation, the formation of new and distinct species during evolution.

Speciation occurs in two ways:

  • Transformation of old species into new species over time.
  • Splitting of a single species into several, that is the multiplication of species.

Speciation Causes

Speciation occurs as a result of several factors which are:

Natural selection

  • As explained by Charles Darwin, different individuals in a species might develop specific distinct characteristics which are advantageous and affect the genetic makeup of the individual.
  • Under such conditions, these characteristics will be conserved, and over time, new species might be formed.
  • However, in this case, the essential aspect of this factor is that speciation occurs only when a single species splits into several species resulting in the multiplication of species.

Genetic drift

  • Genetic drift is the change in the allele frequencies in a population as a result of “sampling error” while selecting the alleles for the next generation from the gene pool of the current population.
  • It has been, however, argued that genetic drift doesn’t result in speciation and just results in evolution, that is, change from one species to another, which cannot be considered speciation.

Migration

  • When a certain number of species from a population migrate from one geographical region to another, the species might accumulate characteristics which are different from that of the original population.
  • Migration usually results in geographical isolation and ultimately leads to speciation.

Natural causes

  • Sometimes, natural events imposed by the environment like a river or a mountain range might cause the separation of what once a continuous population is divided into two or smaller populations.
  • These events result in geographical isolation of the incipient species followed by reproductive isolation leading to speciation.

Types of speciation

Allopatric Speciation

  • Allopatric speciation is the mode of speciation in which the original population is divided into two by a barrier resulting in reproductive isolation.
  • It is based on the concept that new species arise when some physical geographic barrier divides the large population of a species into two or more small populations.
  • The individuals of these isolated populations cannot interbreed because of their physical isolation.

Example of allopatric speciation– The classic example of allopatric speciation is that of Darwin’s finches. The divergent populations of finches inhabiting the Galapagos Islands were observed to have differences in features such as body size, colour, and beak length or shape.

Sympatric Speciation

  • Sympatric speciation is the process of the formation of new species from an original population that are not geographically isolated.
  • It is based on the establishment of new populations of a species in different ecological niches and the reproductive isolation of founders of the new population from the individuals of the source population.

Examples of sympatric speciation:

The North American apple maggot fly is a classic example. As their name indicates, North American apple maggot flies may eat and mate on apple trees. On the other hand, the hawthorn tree was the initial host plant of these insects. It was not until around 200 years ago, when European settlers planted apple trees, that certain flies in the population began to use apples as a food source instead.

Practice question

Example 1. A flash flood carried a raft of Amazon ants away from their original population. There is enough distance between the two groups, that they will never meet in nature again. What type of reproductive barrier is this?

a) behavioural isolation b) temporal isolation

c) gametic isolation d) geographical isolation 

Solution 1: d. The example stated above is geographical isolation.

Example 2. When has speciation occurred?

a) When populations no longer look the same

b) When populations no longer have the same frequency of alleles

c)When populations are living in different environments

d) When populations can no longer interbreed  

Solution 2: Speciation occurs when populations can no longer interbreed.                               

Summary  

  • Speciation is an evolutionary process that results in the emergence of a new species.
  • Allopatric, Peripatric, Parapatric, and sympatric are the four geographic modalities of speciation in nature, depending on the extent to which speciating populations are secluded from each other.
  • The process of speciation in which the original population is separated by a barrier, resulting in reproductive isolation, is known as allopatric speciation.
  • The development of new species from an initial population that is not geographically separated is known as sympatric speciation.

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