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Most multicellular organisms go through a single cell bottleneck in development, a process that ensures subsequent clonality of the cells within the individual. Selection for clonality among cells could reduce costly intra-organismal conflicts that would occur in mixtures of unrelated cells (chimeras). In Dictyostelium discoideum, the usually solitary amoebae aggregate with nearby cells when starving to form a motile, multicellular slug that may be clonal or chimeric. This slug migrates to the soil surface and forms a ball of spores held aloft by a stalk of dead cells. Previous work on D. discoideum has shown that uniclonal slugs migrate further than chimeric slugs of the same size across agar, indicating a functional cost to chimerism. Here we test whether this cost to chimerism results in a fitness cost under more natural conditions. First, we examine migration of slugs across decaying leaves or soil. Second, we examine …