Population genetics of the invasive Argentine ant in its native and introduced ranges

The introduction of a species to a habitat outside its native range can often have grave consequences. Such biological invasions can be economically costly and ecologically destructive. This dissertation describes the population genetics of one such invader, the Argentine ant (Linepithema humile ). In Chapter 1, nuclear microsatellite markers were used to show that introduced populations of the Argentine ant have reduced levels of genetic diversity relative to native populations. This loss of genetic diversity is attributed to a population bottleneck that occurred during the introduction of the Argentine ant to the United States. The resulting genetic homogeneity has decreased the frequency of intraspecific aggression in introduced populations, allowing population densities to increase. The differences in colony structure and population genetics between the native and introduced ranges are examined in Chapter 2. In both ranges, colonies are genetically differentiated whereas the nests within them are not. Moreover, native populations are characterized by a pattern of genetic isolation by distance while introduced populations are genetically homogeneous across broad spatial scales. The genetic similarity of individuals within introduced nests and colonies is much higher than in the native range when considered relative to ancestral levels of genetic diversity. In Chapter 3, mitochondrial DNA sequences and microsatellite allele frequency data were used to reconstruct the phylogenetic relationships among native and introduced populations. The mitochondrial data reveal that several Brazilian populations are phylogenetically distant from populations in Argentina as well as all introduced populations. This suggests that control strategies using parasitoids of Brazilian populations may not be effective for introduced populations. The microsatellite-based phylogeny resolves the relationship among the more similar populations of Argentine ants. These data reveal large-scale biogeographic patterns among native populations in Argentina, and indicate that introduced populations are most similar to native populations in the southern Rio Parana watershed. Thus, future studies of these populations may lead to the discovery of natural enemies that could be used for the biological control of introduced populations.