Social evolution in planarian flatworms

Multicellular organisms are a remarkable feat of cooperation, with the actions of up to billions of cells coordinated to produce a single coherent individual. This project aims to understand the evolution and stability of multicellularity by using the planarian flatworms, an unsual group of animals famed for their remarkable regenerative abilities. This project probes how the worms’ remarkable developmental and reproductive biology affects cooperation and conflict among cells within a worm, and among the worms themselves, and assesses what effect these have on the worms’ ecology.

Cooperation among cells within an organism is favoured because developmental mechanisms ensure that cells within an individual are clonal: development from a single-cell zygote means that all cells are identical, and a strict separation between germ and soma prevents any selfish mutants that arise in the soma from accessing the germline. The planarians, however, lack both mechanisms: many reproduce through fission and never go through a single-cell stage, while those that reproduce sexually have no clear distinction between germ and soma. We might therefore expect cells to have evolved competitive traits that are favoured in competition among cells, but that are detrimental to the animal carrying them.

Although the planarians are well-studied in developmental and regenerative laboratories, this project considers them from a novel perspective, using social evolution theory to understand how multicellularity evolved and flourished. This project offers the opportunity to focus on a number of areas where the worms’ unusual biology intersects social evolution theory and ecology:

- How competition among cells within a worm affect organismal function and competitive ability;
- Whether worms are able to recognize clonemates they recently fissioned from, and whether they modulate selfish competitive traits accordingly;
- How their hermaphroditic mating system (based on reciprocal sperm and egg exchange) aligns with predictions from game theory, and how it maintains stability against reproductive cheats;
- How ejaculates from multiple individuals compete for fertilization opportunities when stored, and how relatedness among developing embryos affects competitive interactions.

For more information, please send a brief outline of your interests and copy of your CV to Ashleigh Griffin at [Email Address Removed]