Fitness trade-offs and developmental constraints in the evolution of soma: an experimental study in a volvocine alga.

Background: The evolution of mortal somatic cells was a critical step in the evolution of complex body plans and the major radiations of multicellular life. In the volvocine green algae, somatic cells are hypothesized to mitigate an increasing cost of reproduction as colony size increases, primarily by providing motility to the colony during reproduction.

Questions: Does selection on colony size cause an evolutionary response in proportion of somatic cells? Does the effect of selection on colony size differ in environments that differ in the importance of motility?

Methods: We subjected an outcrossed population of the volvocine alga to selection on colony size in still and mixed environments.