C factor, a cell-surface-associated intercellular signaling protein, stimulates the cytoplasmic Frz signal transduction system in Myxococcus xanthus.

C factor, an intercellular signaling protein, is required for aggregation and sporulation of the social bacterium, Myxococcus xanthus. We report that C factor, which normally is associated with the cell surface, provides input to the Frz signal transduction cascade. Elements of this cascade have sequence homology to bacterial chemotaxis systems and are known to control the frequency of gliding reversal. Exposure of developing cells of a C-factor-less mutant (csgA) to purified C factor increases the ratio of methylated to nonmethylated FrzCD protein, the Frz homolog of the methyl-accepting chemotaxis proteins. Methylation depends on the cognate methyltransferase FrzF, and its extent increases with the concentration of C factor. C-factor-induced methylation also depends on the product of a gene, called class II, which is necessary in vivo for all known responses to C factor. A model for aggregation is proposed in which C factor stimulates the Frz cascade and thereby decreases cell reversals in a way that preferentially leads cells into an aggregate.

Social evolution in a new environment: the case of introduced fire ants.

The inadvertent introduction of the fire ant Solenopsis invicta to the United States from South America provides the opportunity to study recent social evolution by comparing social organization in native and introduced populations. We report that several important elements of social organization in multiple-queen nests differ consistently and dramatically between ants in Argentina and the United States. Colonies in Argentina contain relatively few queens and they are close relatives, whereas colonies in the United States contain high numbers of unrelated queens. A corollary of these differences is that workers in the native populations are significantly related to the new queens that they rear in contrast to the zero relatedness between workers and new queens in the introduced populations. The observed differences in queen number and relatedness signal a shift in the breeding biology of the introduced ants that is predicted on the basis of the high population densities in the new range. An additional difference in social organization that we observed, greater proportions of permanently unmated queens in introduced than in native populations, is predicted from the loss of alleles at the sex-determining locus and consequent skewing of operational sex ratios in the colonizing ants. Thus, significant recent social evolution in fire ants is consistent with theoretical expectations based on the altered ecology and population genetics of the introduced populations.