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Presentation

Abstract

In Life’s nearly four billion year history, organizational transitions have occurred that fundamentally altered the course of evolution. One of these, multicellularity, arose independently in at least two-dozen lineages, giving rise to a remarkable variety of complex forms. In the volvocine algal family, many transitional structures are retained in extant lineages, ranging from the unicellular, flagellated Chlamydomonas reinhardtii to the extravagant Volvox carterii, which contains as many as 50,000 differentiated cells. Many hypotheses have been suggested for the selective pressure that drove the evolution of multicellularity in this group, but none have been explicitly tested. Here, we tested the hypothesis that multicellular Chalmydomonas reinhardtii can evolve due to predatory selective pressure. By maintaining a continuous co-culture of the unicellular algae C. reinhardtii with the predatory ciliate Paramecium, we were able to select for multicellular phenotypes, due to the increased fitness of algal individuals whose size exceeds the maximum particle size of the predators. After 50 weeks of co-culture, a range of multicellular C. reinhardtii individuals were isolated from the experimental populations. As our research continues, we are implementing a number of genetic and genomic techniques to map these multicellular phenotypes on to specific coding and regulatory changes in the genome of the evolved isolates.

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Apr 11th, 4:40 PM Apr 11th, 5:00 PM

Experimental Evolution of Multicellularity in Chlamydomonas reinhardtii

In Life’s nearly four billion year history, organizational transitions have occurred that fundamentally altered the course of evolution. One of these, multicellularity, arose independently in at least two-dozen lineages, giving rise to a remarkable variety of complex forms. In the volvocine algal family, many transitional structures are retained in extant lineages, ranging from the unicellular, flagellated Chlamydomonas reinhardtii to the extravagant Volvox carterii, which contains as many as 50,000 differentiated cells. Many hypotheses have been suggested for the selective pressure that drove the evolution of multicellularity in this group, but none have been explicitly tested. Here, we tested the hypothesis that multicellular Chalmydomonas reinhardtii can evolve due to predatory selective pressure. By maintaining a continuous co-culture of the unicellular algae C. reinhardtii with the predatory ciliate Paramecium, we were able to select for multicellular phenotypes, due to the increased fitness of algal individuals whose size exceeds the maximum particle size of the predators. After 50 weeks of co-culture, a range of multicellular C. reinhardtii individuals were isolated from the experimental populations. As our research continues, we are implementing a number of genetic and genomic techniques to map these multicellular phenotypes on to specific coding and regulatory changes in the genome of the evolved isolates.