Parapatric speciation

Parapatric speciation is a mode of speciation in which populations of a species that inhabit different parts of its geographical range become distinct species while maintaining a continuous distribution. Unlike allopatric speciation, which involves geographic separation, and sympatric speciation, where speciation occurs within a shared habitat without physical barriers, parapatric speciation involves partial geographic isolation where adjacent populations evolve into distinct species. This process often occurs when a population enters a new niche or habitat, leading to a gradient of environmental conditions across the population's range.

Mechanisms

The primary mechanism behind parapatric speciation is the combination of reduced gene flow and selection across an environmental gradient. This can lead to the evolution of a cline, a gradual change in a trait or genetic composition across the population's range. When the differences across the cline become significant, reproductive isolation may occur, leading to speciation. Key mechanisms include:

• Disruptive selection: Different environmental conditions in adjacent areas may favor different traits at each end of the distribution, leading to divergent evolution.
• Mate preference: Individuals may prefer mates that are phenotypically similar, which can enhance reproductive isolation.
• Hybrid zones: Regions where the ranges of the diverging populations meet and interbreed can form, but hybrids may have reduced fitness, reinforcing the separation.

Examples

One classic example of parapatric speciation is the ring species concept, where populations that are reproductively isolated coexist in adjacent habitats but can interbreed with physically closer populations. The Ensatina salamanders in California have been cited as an example, with distinct subspecies forming a ring around the Central Valley and only the terminal forms being reproductively isolated.

Implications for Conservation

Parapatric speciation highlights the importance of habitat gradients and transitional zones in biodiversity. Conservation efforts should consider these areas as potential hotspots for speciation and genetic diversity. Protecting these zones is crucial for maintaining the evolutionary potential of species facing environmental changes.

Challenges in Study

Studying parapatric speciation poses challenges, as it requires detailed knowledge of the genetic structure, environmental gradients, and reproductive barriers of populations. Moreover, distinguishing parapatric speciation from sympatric or allopatric speciation can be difficult due to the subtle differences in the mechanisms and outcomes of these processes.

See Also

• Speciation
• Allopatric speciation
• Sympatric speciation
• Peripatric speciation
• Evolutionary biology
• Population genetics