Genetic structure of a natural population of Dictyostelium discoideum, a cellular slime mould

Abstract

Dictyostelium discoideum is a eukaryotic microbe feeding on soil bacteria. A first step towards describing the genetic structure of populations of this species was made by examining multiple isolates from a single locale. The isolates were grown clonally and their RFLP patterns compared, using a probe specific for a family of tRNA genes. Thirty-nine types were distinguished in 54 isolates. To determine if genetic exchange occurs among members of the population, an analysis of linkage disequilibrium was performed on the RFLP data. Little disequilibrium was found, implying gene flow in the population. In conflict with this result is the finding that no recombinant progeny were recovered from many attempted crosses between pairs of isolates. The tentative conclusion is that genetic exchange does not in fact occur, and that the observed shuffling of RFLP bands is caused by insertion and excision of transposons known to be associated with the tRNA genes of Dictyostelium.

A linear dominance hierarchy among clones in chimeras of the social amoeba Dictyostelium discoideum

“…The type clone from which nearly all the laboratory clones have been derived, NC4, came from Little Butt's Gap, but was collected considerably earlier, by Raper in 1939(Raper, 1984. For the other clones, we use the clone numbers assigned to them by Francis & Eisenberg (1993). We chose these seven clones from the larger set used in our previous study of mixing and unequal spore/stalk representation.…”

“…We used seven different clones (NC4, NC28.1, NC34.1, NC60.1, NC85.2, NC98.1 and NC105.1) that were collected from Little Butt's Gap, North Carolina (Francis & Eisenberg, 1993). The type clone from which nearly all the laboratory clones have been derived, NC4, came from Little Butt's Gap, but was collected considerably earlier, by Raper in 1939(Raper, 1984.…”

The costs and benefits of being a chimera

“…It makes sense adaptively in getting amoebae away from the starving environment and towards open spaces suitable for spore dispersal (Bonner 1982;Kessin 2001). We used 10 natural clones isolated from the type locality, Little Butts Gap, NC, USA (Francis & Eisenberg 1993;Strassmann et al 2000 We raised clones from spores stored on silica gel using SM/5 plates and the bacteria Klebsiella aerogenes. We added a total of 10 7 amoebae from 1, 2, 5 or 10 clones (in equal proportions) to separate starving plates in 200 µl of water.…”

“…Dictyostelium discoideum is a predator of bacteria and is common in the soil (Bonner 1967;Raper 1984;Francis & Eisenberg 1993). When starving, the usually solitary single-celled amoebae aggregate and form a differentiated multi-cellular organism, which contains 10 4 -10 6 cells when cultured in the laboratory (Bonner 2001).…”

Dictyostelium amoebae lacking an F-box protein form spores rather than stalk in chimeras with wild type

“…One of the problems, as pointed out by Buss and others, is that in the wild, parasitic forms of Dictyostelium should arise that form only spore cells (4)(5)(6). There is genetic diversity in wild-type populations of Dictyostelium from which such variants would be expected to arise over evolutionary time (7). Such parasites, not having to tithe 20% to the stalk cells, would increase in the population and eventually impede the cooperativeness that leads to fruiting body formation.…”