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10:04
Mating and Tetrad Separation of Chlamydomonas reinhardtii for Genetic Analysis
Published on: August 13, 2009
Genetic Predisposition Toward Multicellularity in Chlamydomonas reinhardtii
I-Chen Kimberly Chen1, Shania Khatri1, Matthew D Herron1
1School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA.
Genome Biology and Evolution
|May 17, 2025
Summary
Simple multicellularity evolved in green algae under predation but not settling selection. Ancestral genotype and environment determined the evolutionary transition, with specific founders predisposed to multicellularity.
Area of Science:
- Evolutionary biology
- Cellular biology
- Genetics
Background:
- The transition from unicellular to multicellular life is a major evolutionary event enabling complex adaptations.
- While laboratory evolution has demonstrated the emergence of simple multicellularity from unicellular ancestors, the roles of ancestral genotype and environmental conditions remain underexplored.
Purpose of the Study:
- To investigate how ancestral genotype and environmental context influence the evolution of simple multicellularity.
- To determine if specific genetic backgrounds predispose unicellular organisms to evolve multicellular traits under different selective pressures.
Main Methods:
- Conducted 24 evolution experiments using Chlamydomonas reinhardtii, with each population founded by 10 different strains.
- Applied two distinct selection regimes: predation by Paramecium tetraurelia and settling selection via centrifugation.
- Monitored populations for 40 transfers (approximately 600 generations) and performed whole-genome sequencing on evolved multicellular isolates.
Main Results:
- Heritable multicellular structures evolved in 4 of 12 predation-selected populations, resulting in 6 multicellular isolates.
- No multicellular structures evolved in any of the 12 settling selection populations.
- Whole-genome analysis revealed that all multicellular isolates originated from only two specific ancestral strains.
- Observed variation in cell cluster size among evolved strains, even those derived from the same ancestor.
Conclusions:
- Both deterministic factors (ancestral genotype) and stochastic factors (random mutations and environmental interactions) play crucial roles in the evolution of simple multicellularity.
- Specific genotypes within a genetically diverse unicellular population exhibit a higher propensity to evolve multicellularity under certain environmental conditions.
- Predation pressure appears to be a more effective selective force than passive settling for driving the evolution of multicellularity in this model system.
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