Theoretical and experimental studies on the fire ant Solenopsis invicta

This dissertation contains four chapters concerning the biology of the fire ant Solenopsis invicta. The first two chapters develop theoretical models for analyzing cytonuclear genetic structure for either a cytoplasmic and nuclear marker in haplodiploid species, such as S. invicta, or a cytoplasmic and X-linked marker in diploid species. The first study defines disequilibria that quantify nonrandom cytonuclear associations and delimits their basic Hardy-Weinberg dynamics. This study also develops and extensively analyzes continent-island, hybrid zone models whereby individuals from genetically differentiated populations migrate into and mate within a zone of admixture.; The second chapter extends this hybrid zone framework to include stepping-stone models of migration. Equilibrium clines are examined for allele frequencies, cytonuclear disequilibria, and frequencies of pure parental types under differential gene flow by sex and direction. An application to cytonuclear data from a hybrid zone between S. invicta and S. richteri indicates that the stepping-stone model cannot explain the distribution of cytonuclear genotypes through the hybrid zone, because equilibrium has not yet been reached.; The final two chapters present the results of empirical investigations on queen recruitment in S. invicta. The third chapter assesses nestmate queen relatedness and the genetic similarity of neighboring nests in polygyne (multiple-queen) S. invicta using nuclear and mitochondrial markers. Estimates of queen relatedness calculated with both types of markers do not differ statistically from zero, and there is no significant relationship between the genetic similarity and geographic proximity of nests. These results suggest that nestmate queens represent a random sample of queens within the site in which they reside.; The fourth chapter examines patterns of new queen recruitment in introduced polygyne S. invicta. Newly recruited queens were identified using four physiological markers, and genotypic data from nuclear and mitochondrial markers were used to estimate relatedness of new nestmate queens. In total, 1.66% of the queens collected were deemed new recruits. The relatedness of these queens to each other and to the older queens within nests did not differ significantly from zero. In contrast to theoretical expectations, the number of new queens recruited within nests was not correlated with the number of older queens present.