Evol Ecol Res 7: 263-271 (2005) Full PDF if your library subscribes.
A cost to chimerism in Dictyostelium discoideum on natural substrates
David I. Castillo,* Ghislaine T. Switz, Kevin R. Foster, David C. Queller and Joan E. Strassmann
Department of Ecology and Evolutionary Biology, Rice University, MS 170, 6100 Main Street, Houston, TX 77005, USA
Author to whom all correspondence should be addressed.
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 migration up through layers of these substrates, which most closely reflects the natural migration of D. discoideum slugs to the soil surface. In most trials, chimeras performed worse than single clones. Our results indicate that chimerism in D. discoideum has a real fitness cost in the wild, likely to be compensated only by the larger size chimeras can attain in nature.
Keywords: chimera, conflict, cooperation, social amoebae.
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