Digest: Pelagic habitats promote speciation but constrain morphological evolution.

What happens when ecological factors predicted to promote evolutionary change coincide with factors predicted to constrain it? A recent study by Burress and Hart (2024) shows that the transition of North American minnows from a competitive and complex benthic habitat to a noncompetitive and homogeneous pelagic habitat is associated with an increase in speciation rates but a decrease in rates of morphological evolution. These results demonstrate that different dimensions of evolutionary change may respond to different ecological factors.