Kin discrimination increases with genetic distance in a social amoeba.

Department of Ecology and Evolutionary Biology, Rice University, Houston, Texas, USA.
PLoS Biology (Impact Factor: 11.77). 12/2008; 6(11):e287. DOI: 10.1371/journal.pbio.0060287
Source: PubMed

ABSTRACT In the social amoeba Dictyostelium discoideum, thousands of cells aggregate upon starvation to form a multicellular fruiting body, and approximately 20% of them die to form a stalk that benefits the others. The aggregative nature of multicellular development makes the cells vulnerable to exploitation by cheaters, and the potential for cheating is indeed high. Cells might avoid being victimized if they can discriminate among individuals and avoid those that are genetically different. We tested how widely social amoebae cooperate by mixing isolates from different localities that cover most of their natural range. We show here that different isolates partially exclude one another during aggregation, and there is a positive relationship between the extent of this exclusion and the genetic distance between strains. Our findings demonstrate that D. discoideum cells co-aggregate more with genetically similar than dissimilar individuals, suggesting the existence of a mechanism that discerns the degree of genetic similarity between individuals in this social microorganism.

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    ABSTRACT: Dictyostelium discoideum, a microbial model for social evolution, is known to distinguish self from non-self and show genotype-dependent behavior during chimeric development. Aside from a small number of cell-cell recognition genes, however, little is known about the genetic basis of self/non-self recognition in this species. Based on the key hypothesis that there should be differential expression of genes if D. discoideum cells were interacting with non-clone mates, we performed transcriptomic profiling study in this species during clonal vs. chimeric development. The transcriptomic profiles of D. discoideum cells in clones vs. different chimeras were compared at five different developmental stages using a customized microarray. Effects of chimerism on global transcriptional patterns associated with social interactions were observed.
    BMC Genomics 07/2014; 15(1):616. · 4.04 Impact Factor
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    ABSTRACT: Fusion between multicellular individuals is possible in many organisms with modular, indeterminate growth, such as marine invertebrates and fungi. Although fusion may provide various benefits, fusion usually is restricted to close relatives by allorecognition, also called heterokaryon or somatic incompatibility in fungi. A possible selective explanation for allorecognition is protection against somatic parasites. Such mutants contribute less to colony functions but more to reproduction. However, previous models testing this idea have failed to explain the high diversity of allorecognition alleles in nature. These models did not, however, consider the possible role of spatial structure. We model the joint evolution of allorecognition and somatic parasitism in a multicellular organism resembling an asexual ascomycete fungus in a spatially explicit simulation. In a 1,000-by-1,000 grid, neighboring individuals can fuse, but only if they have the same allotype. Fusion with a parasitic individual decreases the total reproductive output of the fused individuals, but the parasite compensates for this individual-level fitness reduction by a disproportional share of the offspring. Allorecognition prevents the invasion of somatic parasites, and vice versa, mutation towards somatic parasitism provides the selective conditions for extensive allorecognition diversity. On the one hand, if allorecognition diversity did not build up fast enough, somatic parasites went to fixation; conversely, once parasites had gone to fixation no allorecognition diversity built up. On the other hand, the mere threat of parasitism could select for high allorecognition diversity, preventing invasion of somatic parasites. Moderate population viscosity combined with weak global dispersal was optimal for the joint evolution of allorecognition and protection against parasitism. Our results are consistent with the widespread occurrence of allorecognition in fungi and the low degree of somatic parasitism. We discuss the implications of our results for allorecognition in other organism groups.
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    ABSTRACT: Altruism is a ubiquitous strategy among organisms ranging from microbes to mammals. Inclusive fitness theory indi-cates that altruistic strategies can be beneficial when an altruist acts to benefit organisms that share its genes. It is common for such altruistic strategies to be negatively af-fected by cheaters that do not act altruistically. A more sub-tle form of cheating involves altruists that are more selective. For example, a selective organism may benefit from a distant kin's altruistic actions without reciprocating. We consider an organism's kin inclusivity level to be the maximum num-ber of mutational differences where the other organism will be considered kin. We use evolving computer programs (dig-ital organisms) to explore competitions among organisms with different kin inclusivity levels. Using competition as-says that vary environmental parameters, we find that high mutation rates favor more inclusive colonies. When we com-peted colonies with a wide range of kin inclusivity levels, we found that moderate mutation rates and populations sizes led to intermediate inclusivity levels winning the competi-tions, indicating that extreme inclusivity levels were not al-ways optimal. However, when organisms could set their own kin inclusivity level, we found that high mutation rates se-lected for highly inclusive organisms.
    GECCO 2014, Vancouver, BC, Canada; 07/2014

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