Group Formation, Relatedness, and the Evolution of Multicellularity

Roberta M Fisher,Charlie K Cornwallis,Stuart A West

doi:10.1016/j.cub.2013.05.004

Roberta M Fisher, Charlie K Cornwallis + Show 1 more

Open Access

https://doi.org/10.1016/j.cub.2013.05.004

Copy DOI

Journal: Current Biology	Publication Date: Jun 1, 2013
Citations: 194	License type: cc-by

Affiliation: University of Oxford, Lund University

Abstract

The evolution of multicellular organisms represents one of approximately eight major evolutionary transitions that have occurred on earth. The major challenge raised by this transition is to explain why single cells should join together and become mutually dependent, in a way that leads to a more complex multicellular life form that can only replicate as a whole. It has been argued that a high genetic relatedness (r) between cells played a pivotal role in the evolutionary transition from single-celled to multicellular organisms, because it leads to reduced conflict and an alignment of interests between cells. We tested this hypothesis with a comparative study, comparing the form of multicellularity in species where groups are clonal (r = 1) to species where groups are potentially nonclonal (r ≤ 1). We found that species with clonal group formation were more likely to have undergone the major evolutionary transition to obligate multicellularity and had more cell types, a higher likelihood of sterile cells, and a trend toward higher numbers of cells in a group. More generally, our results unify the role of group formation and genetic relatedness across multiple evolutionary transitions and provide an unmistakable footprint of how natural selection has shaped the evolution of life.

Highlights

We found that species with clonal groups had significantly higher numbers of cell types and a significantly higher probability of having sterile cells
We found that species with clonal groups had a higher proportion of sterile cells and a greater number of cells, but that these differences were nonsignificant
We have shown how a higher relatedness between cells leads to a higher likelihood of obligate multicellular groups, a higher number of cell types, and a higher likelihood of sterile cells (Figures 2, 3, and S3)

Summary

Introduction

We use a phylogenetically based [19] comparative study to test how the relatedness between interacting cells influenced both the likelihood of the major evolutionary transition to obligate multicellularity and the level of sociality in multicellular groups. Causality and Assumptions We have examined how relatedness influences both whether a transition to obligate multicellularity has occurred and the different traits that determine the level of sociality, such as whether there are sterile cells in the group.

Results

Conclusion