9707331 Ross Considerable attention has focused recently on the reduction in genetic diversity that follows founder events and other types of severe reductions in population size (bottlenecks). One reason for this interest is that reduced genetic variation may affect the subsequent ability of populations to respond to natural selection. Moreover, changes in the nature and extent of genetic variation following a bottleneck may lead to genetic incompatibilities between parental and founder populations, one outcome of which may be speciation. Thus, the genetic changes accompanying bottlenecks are of basic scientific interest because of their possible role in the natural processes of adaptation and species diversification, and of applied interest because endangered species subjected to bottlenecks may lack the ability to respond to subsequent environmental change. The aim of this project is to describe the effects of a well-documented founder event on variation in five different classes of genetic markers in wild populations of the fire ant Solenopsis invicta. The markers to be used are 78 nuclear markers derived from protein electrophoresis, seven microsatellite DNA loci, 64 RAPD DNA markers, the locus or loci responsible for sex determination, and markers of the mitochondrial DNA. Results from these five sets of markers are complementary for studying the effects of a bottleneck because they have different genetic architectures, are under different selective regimes, and have different modes of inheritance. Electrophoretic markers represent protein-encoding nuclear loci with modest variation that generally are not under strong selection. Microsatellites are repetitive nuclear sequences in non-coding regions that harbor extensive polymorphism. RAPDs are randomly amplified nuclear sequences also assumed to be in non-coding regions that display simple presence/absence polymorphisms. The sex-determining locus is a regulatory element under strong selection that maintains extensive polym orphism comparable to or even surpassing that of microsatellites. Finally, mitochondrial DNA provides a set of markers that are maternally inherited, in contrast to the biparental inheritance of the four classes of nuclear genes. The composite results will be used to test theories that predict how bottlenecks affect various classes of genes and how the evolutionary potential of bottlenecked populations is altered. The results also may allow estimation of the number of fire ant queens constituting the original founder population in the U.S.
