Experimental sexual selection in Chlamydomonas.

Area of Science:

• Evolutionary biology
• Microbial genetics
• Algal research

Background:

• Chlamydomonas reinhardtii is a model organism for studying sexual reproduction and evolution.
• Understanding the drivers of sexual isolation and speciation is crucial in evolutionary biology.

Purpose of the Study:

• To investigate the effects of long-term sexual and asexual selection on Chlamydomonas reinhardtii.
• To determine if divergent selection can lead to sexual isolation and incipient speciation.

Main Methods:

• Propagating sexual and asexual lines for 100 sexual and 1000 vegetative cycles, respectively.
• Applying contrasted environments (liquid and solid media) and different mating transfer strategies (single zygote vs. mass transfer).
• Monitoring zygote production, mating type system, and evidence of sexual isolation.

Main Results:

• Sexual selection significantly increased zygote production by two orders of magnitude, primarily due to spontaneous mating.
• Asexual lines became sexually sterilized, and sexual lines shifted towards homothallism.
• No significant environment-specific mating or sexual isolation indicative of incipient speciation was observed.

Conclusions:

• Sexual selection can rapidly alter mating behavior and mating systems in Chlamydomonas reinhardtii.
• Long-term selection experiments may not be sufficient to induce sexual isolation due to the saltatory evolution of mating-type genes.
• Mating-type gene transposition to an autosome may explain the observed shift to homothallism.