Speciation: Causes, Process, Types and Examples

Speciation is the evolutionary process in which populations evolve into different species. It is critical for understanding biodiversity and how life forms evolve from a common ancestor to adapt to varied surroundings.

It is a process by which one or more species diverge from an existing species. It happens when there is little to no gene flow between two populations due to their geographic and reproductive isolation.

But within the separated populations, inbreeding persists, giving rise to an increasing number of generations. These two groups’ members will eventually be unable to procreate with one another, even if they do come into contact. Different changes in a subpopulation are accumulated by genetic drift in subsequent generations. Additionally, the way natural selection functions in these various geographic regions may also vary. For instance, eagles may drive out crows from a subpopulation’s region.

However, in the other subpopulation, this might not hold true, and as a result, there will be a very high crow population. That’s why the green variety will be strongly selected at the second site but not selected at the first.

Causes of Speciation

1. Geographic Isolation (Allopatric): Physical barriers (mountains, rivers, or distance) prevent gene flow between populations, causing genetic divergence over time.
2. Reproductive Isolation: Barriers that prevent successful reproduction between populations, even when they are in the same location. These include:
   • Prezygotic Barriers: Prevent fertilization (e.g., behavioral differences, temporal isolation).
   • Postzygotic Barriers: Reduce the viability or fertility of offspring (e.g., hybrid sterility).
3. Genetic Drift: Random changes in allele frequencies can cause populations to diverge, especially in small populations.
4. Natural Selection: Differential survival and reproduction based on environmental pressures can drive populations to adapt to different niches, leading to speciation.
5. Mutation: New genetic variations arise from mutations, potentially creating new traits that contribute to divergence between populations.
6. Hybridization: When two distinct species interbreed, hybrids may form. If the hybrids are fertile and can adapt to an ecological niche, new species may arise.

Process of Speciation

1. Isolation: A population becomes isolated from others, either geographically or reproductively.
2. Divergence: Over time, genetic differences accumulate between the isolated populations due to mutation, genetic drift, and natural selection.
3. Reproductive Isolation: Eventually, the populations become so different that even if they come back into contact, they can no longer interbreed and produce fertile offspring.
4. Formation of New Species: At this stage, the isolated populations have evolved into distinct species.

Types of Speciation

1. Allopatric : Occurs when a population is geographically isolated, leading to the divergence of species.
   • Example: Darwin’s finches on the Galápagos Islands. Each species of finch evolved to have different beak shapes, adapted to different food sources.
2. Sympatric : Occurs without geographic isolation, typically through reproductive isolation, such as different behaviors or preferences within the same location.
   • Example: Apple maggot flies, which started to diverge based on the fruit they fed on (apples vs. hawthorns).
3. Peripatric Speciation: A subtype of allopatric, where a small group becomes isolated on the edge of a larger population. Due to the small size, genetic drift can play a more significant role.
   • Example: Polar bears evolved from a population of brown bears that became isolated in the Arctic region.
4. Parapatric Speciation: Occurs when populations are adjacent to each other but do not mate randomly across the population, often due to different environmental pressures or behaviors.
   • Example: Grass species that grow on contaminated soils vs. non-contaminated soils.

Examples of Speciation

1. Cichlid Fish in African Lakes:
   • Over hundreds of species of cichlid fish have evolved in Lake Victoria due to varying ecological niches and behavioral isolation.
2. Galápagos Tortoises:
   • Different species of giant tortoises evolved on different islands of the Galápagos, each adapted to the specific environment on their island.
3. Ensatina Salamanders (Ring Species):
   • In California, different populations of the Ensatina salamander exhibit varying degrees of reproductive isolation along a geographic ring, leading to the emergence of different species.

In summary, genetic alterations, reproductive isolation, and geographic isolation all work together to drive the complicated process of speciation. There are many examples of speciation in nature, and the types might differ depending on the mechanism of isolation and divergence.

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