Speciation

Rucete ✏ Biology In a Nutshell

1. What Is Speciation?

Speciation is the evolutionary process by which new species arise from a common ancestor.
It involves the accumulation of genetic differences that prevent interbreeding.

2. Allopatric Speciation

• Occurs when a population is geographically separated (e.g., by mountains or rivers).
• Physical isolation prevents gene flow, leading to genetic divergence over time.
• Eventually, the separated populations become reproductively isolated and form new species.

3. Sympatric Speciation

• Occurs without geographic separation.
• New species evolve from a single ancestral species living in the same area.

a) Balanced Polymorphism

• Different phenotypes within a population prefer different niches or mates, leading to reproductive isolation.

b) Polyploidy

• Occurs mainly in plants.
• Results from an error in cell division that produces extra sets of chromosomes (e.g., 4n instead of 2n).
• Polyploid individuals are reproductively isolated from diploid relatives.

c) Hybridization

• Two different species mate and produce hybrid offspring.
• If hybrids are fertile and reproductively isolated, new species may form.

4. Adaptive Radiation

• A single ancestral species rapidly evolves into many new species, each adapted to a specific environment or niche.
• Often occurs after colonization of new areas or mass extinction events.
• Example: Darwin’s finches in the Galápagos Islands.