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: 9.34). 12/2008; 6(11):e287. DOI: 10.1371/journal.pbio.0060287
Source: PubMed


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In social amoebae such as Dictyostelium discoideum, cells aggregate to form a multicellular slug that migrates and then forms a fruiting body, which contains live spores (which go on to make new amoebae) and dead stalk cells. Unlike animals where all the cells descend from one fertilized egg, social amoeba fruiting bodies can contain cells with different genotypes. This potential for chimerism creates a conceptual problem in that “cheater” cells could arise that preferentially become reproductive spores and force the victims to become stalk cells and die. One way that amoebae could avoid being cheated is if they recognize and preferentially aggregate with genetically similar cells while avoiding genetically distant cells—a process called kin discrimination. We tested whether cells of D. discoideum could discriminate in this way. We mixed cells from genetically distinct strains and found that they segregate during multicellular development. The degree of segregation increases in a graded fashion with the genetic distance between strains. Our results demonstrate the existence of kin discrimination in D. discoideum, an ability that is likely to reduce the potential for cheating and ensure that the death of the stalk cells provides a fitness advantage to related individuals.

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    • "Once cooperation is established in a population, more advanced mechanisms, which rely on cooperators already present in a population, like kin discrimination or other active forms of positive assortment, may evolve to further stabilize cooperative behavior, see e.g. [1] [62] [63] [64] [65] [66] [9]. "
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    ABSTRACT: Cooperative behaviour is widespread in nature, even though cooperating individuals always run the risk of being exploited by free-riders. Population structure effectively promotes cooperation given that a threshold in the level of cooperation was already reached. However, the question how cooperation can emerge from a single mutant, which cannot rely on a benefit provided by other cooperators, is still puzzling. Here, we investigate this question for a well-defined but generic situation based on typical life cycles of microbial populations where individuals regularly form new colonies followed by growth phases. We analyse two evolutionary mechanisms favouring cooperative behaviour and study their strength depending on the inoculation size and the length of a life cycle. In particular, we find that population bottlenecks followed by exponential growth phases strongly increase the survival and fixation probabilities of a single cooperator in a free-riding population. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
    Full-text · Article · May 2015 · Journal of The Royal Society Interface
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    • ") 、 黑 猩 猩 (Chimpanzee) (Morin et al., 1994)。更有趣的是, 在 对盘基网柄菌(Dictyostelium discoideum) (Ostrowski et al., 2008) 、 酵 母 菌 (Saccharomyces cerevisiae) "

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    • "In the case that a clan altruist is related to a clone altruist, the clan altruist will behave altruistically to the clone altruist, but the clone altruist will not reciprocate . In this case, the clone altruist would " cheat " their clan altruist relatives, demonstrating kin discrimination [18]. Without mechanisms in place for organisms to detect and prevent cheating behaviors based on kin inclusivity levels, clone altruists are likely to take over in highly-related populations . "
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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.
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