Allopatric speciation in riverine fishes is often assumed to be ecologically neutral, with divergence driven primarily by geographic isolation and genetic drift. However, recent work on darters from the Central Highlands of the United States reveals that ecological divergence during allopatry is highly variable and context dependent. By integrating phylogenomics, morphology, diet, and environmental data, Stokes et al. (2026) demonstrate that phenotypic divergence can arise in allopatrically distributed riverine fish species. However, the degree of phenotypic disparity is not predicted by divergence time, genomic isolation, or geographic distance, highlighting a contingent role for ecology in shaping evolutionary outcomes under allopatry.
Delmondes et al. (Mon,) studied this question.