Assessing genetic structure with multiple classes of molecular markers: A case study involving the introduced fire ant Solenopsis invicta

We used 30 genetic markers of 6 different classes to describe hierarchical genetic structure in introduced populations of the fire ant Solenopsis invi cta. These included four classes of presumably neutral nuclear loci (allozy mes, codominant random amplified polymorphic DNAs (RAPDs), microsatellites, and dominant RAPDs), a class comprising two linked protein-coding nuclear loci under selection, and a marker of the mitochondrial DNA (mtDNA). Patter ns of structure revealed by F statistics and exact tests of differentiation were highly concordant among the four classes of neutral nuclear markers, although the microsatellites were the most effective markers for detecting structure. The results from the mtDNA complemented those from the neutral n uclear markers by revealing that strong limitations to female-mediated gene flow were the cause of the local structure registered by the nuclear marke rs. The pattern of structure inferred from the selected nuclear loci was ma rkedly different from the patterns derived from the other sets of markers b ut was predictable on the basis of the presumed mode of selection acting on these loci. In general, the results for all six classes of markers can be explained by known features of the social and reproductive biology of fire ants. Thus, the results from these diverse sets of markers, combined with d etailed natural history data, provide an unusually complete picture of how the fundamental evolutionary forces of gene flow, drift, and selection gove rn the distribution of genetic variation within and between fire ant popula tions.