High relatedness in a social amoeba: the role of kin-discriminatory segregation

Abstract

A major challenge for social theory is to explain the importance of kin discrimination for the evolution of altruism. One way to assess the importance of kin discrimination is to test its effects on increasing relatedness within groups. The social amoeba Dictyostelium discoideum aggregates to form a fruiting body composed of dead stalk and live spores. Previous studies of a natural population showed that where D. discoideum occurs in the soil, multiple clones are often found in the same small soil samples. However, actual fruiting bodies usually contain only one clone. We here performed experiments to gauge the effect of kin-discriminatory segregation on increasing relatedness. We mixed co-occurring clones from this population using a relatedness level found in small soil samples. We found a lower proportion of uniclonal fruiting bodies and a lower level of relatedness compared with natural fruiting bodies. We found that the amount of relatedness increase attributable to kin-discriminatory segregation was small. These findings suggest a relatively minor influence of kin-discriminatory segregation on relatedness in D. discoideum. We discuss our results comparing with the results of previous studies, including those of wild clones and laboratory mutants. We ask why wild clones of D. discoideum exhibit a low degree of kin-discriminatory segregation, and what alternative factors might account for high relatedness in D. discoideum.

Evidence of taxa-, clone-, and kin-discrimination in protists: ecological and evolutionary implications

“…Moreover, a positive relation has been documented between the degree of genetic distance and the degree of recruitment of cells for the formation of fruiting bodies among clone-isolates from three social Mycetozoans ( D. discoideum , D. purpureum , P. violaceum ) collected in diverse localities (Mehdiabadi et al 2006; Ostrowski et al 2008; Kalla et al 2011). This raises the question if social amoebae can or need to discriminate kin from non-kin, but this possibility needs unequivocal confirmation that kin discrimination has an adaptive value for the population structure of social Dictyostelium or Polysphondylium considering that their fruiting bodies in the wild are often composed of clonal clusters (Gilbert et al 2012). Furthermore, because studies with another social amoebae, D. giganteum , have generated inconclusive results, in which cell-lineages collected from the wild and grown together cluster in fruiting bodies of variable degree of chimerism, aggregation could result from epigenetic phenomena (i.e.…”

“…Spatio-temporal co-occurrence of genetic closely related individuals might be a byproduct of opportunistic colonization of patchy/ephemeral resources, where first clones arrive and proliferate while outcompeting others, or in asexual propagation of cells during vegetative cycles, such as those described in Dictyostelium and Tetrahymena (Gilbert et al 2012), or driven by immune responses by a host, like in Plasmodium (Nkhoma et al 2012). When being sampled, such clones could give us the impression of intrinsic kin-biased aggregation, kin-discrimination, or even kin-recognition, when in fact their close genetic proximity results from epigenetic phenomena, i.e.…”

Precarious development: The uncertain social life of cellular slime molds

“…Interactions studied exclusively in the laboratoryas is typical of microbes-can fall short of capturing the richness that exists in the wild. In this regard, the field of slime mold biology has long held, and continues to foster, work that traverses boundaries between laboratory and field (1,7,10).…”

“…Such "cheater" types threaten persistence of altruists. How self-sacrificial behavior is thus maintained in the face of conditions that would seem to select for its elimination has motivated numerous studies (7).…”

Histocompatibility as Adaptive Response to Discriminatory Within-Organism Conflict: A Historical Model

“…Such organisms may exhibit discriminatory conflict but not histocompatibility. A possible example of such an organism is the cellular slime mold Dictyostelium discoideum, which exhibits some evidence of discriminatory withinorganism conflict (Buttery et al 2009;Li et al 2014) but weak histocompatibility-like behavior (Gilbert et al 2012). …”