One of the primary goals of biological research is to understand the forces that maintain biodiversity. One powerful mechanism that leads to the maintenance of diversity is "nontransitive interactions." Nontransitive interactions occur when the dominance relationships among three or more players are not hierarchical, such that A>B, B>C, and C>A. Because no one competitor is superior to all others, diversity can be maintained in the absence of environmental variation. These interactions are thought to be important in preserving both species diversity and genetic diversity within species. Nevertheless, few studies have linked variation observed in nature with empirical tests of theory. The proposed work examines natural isolates of the insect-parasitic bacterium, Xenorhabdus bovienii. Assays of the bacteriocins (narrow-spectrum antibiotics) produced by these isolates suggest that nontransitive interactions may be important in maintaining diversity even at small spatial scales. The researchers will further characterize these antibiotics, and will use these bacterial isolates to rigorously test theoretical models of ecological dynamics. In addition, they will examine whether interactions among bacteria within an insect host have consequences for the insect and other species in the community. Finally, they will experimentally test theory explaining why bacteria resistant to these antibiotics do not come to predominate in the environment.
This work will increase our knowledge of an agriculturally, and potentially pharmaceutically, important system. Moreover, this work will test the assumptions and predictions of theory that can be applied generally to other systems. It will also involve active participation of eight undergraduates in all aspects of research, as well as the mentorship of a graduate student.
