Biology – Evolution | e-Consult

Sympatric speciation occurs when new species arise within the same geographic area. This is a more complex process than allopatric speciation, as it requires mechanisms to prevent gene flow between diverging populations while they are in close proximity. The key mechanisms driving sympatric speciation are:

• Disruptive Selection: Within a single population, there is variation in traits. Environmental conditions favor extreme phenotypes (e.g., very large or very small body size). This leads to the divergence of the population into two or more distinct groups, each adapted to a different niche. Over time, these groups may become reproductively isolated.
• Sexual Selection: Differences in mate choice can drive reproductive isolation. If individuals with certain traits are more attractive to potential mates, those traits will become more common. This can lead to the evolution of reproductive isolation based on mate preferences. For example, if females prefer males with a specific plumage colour, males with different colours may be less successful at mating, leading to reproductive isolation.
• Ecological Specialization: Populations may specialize on different resources within the same environment. This can lead to reproductive isolation if the specialized populations develop different mating rituals or timing of reproduction.

Reproductive isolation can arise through various mechanisms in sympatric speciation, including:

• Changes in Mating Signals: Differences in courtship displays or signals can prevent interbreeding.
• Changes in Timing of Reproduction: Differences in breeding seasons can prevent interbreeding.
• Development of Different Niche Requirements: Populations may evolve to occupy different ecological niches, leading to reproductive isolation.

Example: Apple maggot flies (Rhagoletis pomonella) are a good example of sympatric speciation. The ancestor of this species laid its eggs on hawthorn fruits. However, a new population arose that began laying its eggs on apples, which are less attractive to the hawthorn-laying ancestor. This difference in host preference has led to reproductive isolation and the formation of two distinct species.