During long-term growth in static liquid culture,  Pseudomonas fluorescens diversifies into distinct colony types with the following characteristics: wrinkly spreaders that form biofilms at the oxygen-rich surface, smooth morphs that grow freely in the oxygen-poor bottom layer, and fuzzy types that colonise the intermediate zone. Which one of the following evolutionary processes best explains this ecological diversification?

Correct option is B

Correct Answer:  (b)
Explanation: The diversification of  Pseudomonas fluorescens into multiple morphotypes occupying distinct oxygen-defined niches reflects adaptation to different microhabitats within the same environment. Each morph exhibits traits that enhance fitness in its specific zone, such as biofilm formation at the surface or free-living growth in low-oxygen regions. This pattern is characteristic of adaptive radiation, where a single ancestral population rapidly diversifies into ecologically specialized forms under divergent selection pressures.
Information Booster
· Adaptive radiation occurs when ecological opportunity allows diversification into multiple niches.
· The static liquid culture creates strong spatial gradients, especially of oxygen.
· Wrinkly spreaders gain fitness by forming biofilms at the air–liquid interface.
· Smooth morphs are better adapted to planktonic growth in oxygen-poor zones.
· Natural selection, not chance alone, drives the maintenance of these distinct morphs.
Additional Knowledge
Genetic drift is unlikely to consistently produce morphs precisely suited to specific microhabitats, making option (a) inappropriate. Coevolution implies reciprocal evolutionary change between interacting lineages, which is not required to explain this pattern. Convergent evolution involves unrelated species independently evolving similar traits, whereas the observed diversity arises within a single bacterial species. Thus, adaptive radiation best explains the observed ecological diversification.