The purpose of this project is to understand the selective pressures that drove the evolution of cellular differentiation in the colonial volvocine algae (Volvox and its close relatives). Some species of volvocine algae have two cell types: germ cells specialized for reproduction and sterile somatic cells specialized for motility. Trends among species suggest that this differentiation may have evolved in response to the increasing cost of reproduction in large colonies. To test this hypothesis, costs of reproduction will be measured in a colonial volvocine alga, Pleodorina starrii, artificially selected for large and small size.
The evolution of sterile somatic cells was a critical step in the origin of multicellular organisms, allowing further differentiation into many cell types and the development of complex body plans. The increase in complexity allowed by the development of different functional cell types facilitated the dramatic radiations of large multicellular organisms such as plants and animals. The volvocine algae are a model system for the evolution of multicellularity; understanding the origins of cellular differentiation in this group can shed light on how such differentiation originated in other groups. Furthermore, because somatic cells sacrifice their own reproduction to benefit the colony, understanding the evolution of soma has implications for the evolution of altruism and cooperation in general.
