Which mode of speciation occurs when two populations have continuous distributions and some phenotypes are more favorable in different parts?

• A. Allopatric speciation
• B. Sympatric speciation
• C. Parapatric speciation
• D. Recognition species concept

Answer: (C)

This scenario illustrates parapatric speciation. In a continuous range, neighboring populations experience different environmental conditions, so distinct phenotypes are favored in different parts of the range. Gene flow still occurs between adjacent populations, but selection creates a gradient that pushes populations toward different adaptations. Over time, this divergent selection can lead to reproductive isolation, especially if hybrids have lower fitness in the contact zone or if assortative mating develops, solidifying the split despite ongoing gene flow. The other options don’t fit: geographic separation without contact points describes allopatric, divergence within a single area without a spatial gradient describes sympatric, and the recognition species concept is about mate recognition rather than a mode of speciation.