The incidental response to uniform natural selection

Area of Science:

• Evolutionary biology
• Microbial adaptation
• Genetics

Background:

• Populations exposed to novel environments often adapt.
• Adaptation to new conditions can lead to reduced fitness in ancestral environments.
• Genetic drift and founder effects can influence trait variation in newly founded populations.

Purpose of the Study:

• To investigate adaptation in a unicellular organism under novel growth conditions.
• To examine the consequences of adaptation on fitness in the original environment.
• To explore the role of sampling error in generating trait variation.

Main Methods:

• Utilized 240 replicate lines of Chlamydomonas, a unicellular chlorophyte.
• Initiated cultures from photoautotrophic ancestors.
• Cultured all lines as heterotrophs in the dark for several hundred generations.

Main Results:

• All replicate lines successfully adapted to heterotrophic dark growth.
• Adapted lines showed impaired performance in light conditions.
• Significant variation in colony morphology, uncorrelated with fitness, emerged across lines.

Conclusions:

• Adaptation to novel environments can result in trade-offs and reduced ancestral fitness.
• Random genetic variation among founders (sampling error) likely explains uncorrelated trait diversification.
• Divergence between closely related species may arise from sampling error, not solely natural selection.