In partial fulfillment of the requirements for the degree of

Master of Science in Biology

in the

School of Biological Sciences

Charles Lindsey

Will defend his thesis

“Phylotranscriptomics of the volvocine algae:

A model clade for the study of differentiated multicellularity”

Friday, January 15, 2021

10 AM

https://bluejeans.com/772512341

Thesis Advisor:

Dr. Frank Rosenzweig

School of Biological Sciences

Georgia Institute of Technology

Committee Members:

Dr. Matthew Herron

School of Biological Sciences

Georgia Institute of Technology

 Dr. Joseph Lachance

School of Biological Sciences

Georgia Institute of Technology

Abstract: The volvocine algae, which include the single-celled species Chlamydomonas reinhardtii and the colonial species Volvox carteri, present an attractive model for studying the evolution of multicellularity and cellular differentiation. Many phylogenetic studies that trace the evolutionary history of this group have relied on datasets of one to a few genes for their phylogenetic inferences and ancestral character state reconstructions. These studies suggest that multicellularity evolved only once in the volvocine algae, that each of the three colonial families are monophyletic, and that there have been at least three independent origins of cellular differentiation in this group. We performed RNA-Seq on 55 strains representing 46 volvocine algal species, then generated a dataset consisting of transcripts from 40 single-copy, protein-coding nuclear genes. The predicted amino acid sequences of these genes were subjected to maximum likelihood, Bayesian inference, and coalescent-based analyses. These phylogenetic inferences suggest that multicellularity has evolved independently at least twice among the volvocine algae, and that the three colonial species do not form a clade, as previously thought. We also find that the colonial family Goniaceae is not monophyletic. Our analyses support previous findings that cellular differentiation independently evolved at least three times within this group. These results represent the most taxonomically comprehensive phylogeny yet produced using a nuclear dataset for the volvocine algae, and will serve as a valuable resource for future studies of this evolutionary important group.