Date of Award
Master of Science (MS)
Zungoli, Patricia A.
Turnbull , Matthew
Lawton-Rauh , Amy
Bridges , William
Pachycondyla chinensis (Emery) (Formicidae: Ponerinae), is an ancestral ant introduced from Asia. It is considered a pest species of medical and ecological concern. Since its initial 1932 documentation occurring in three Southeastern U.S. states at relatively low frequencies, the invasion of P. chinensis has spread to at least three additional states in discontinuously widespread populations that are locally abundant. Little is known about P. chinensis population structure and reproduction, and an investigation into these strategies offers insight into the means by which this pest species proliferates, and ultimately, can assist in the design of management strategies. The objectives of this research were to explore the utility of microsatellite loci found in this species as a monitoring tool, population structure of colonies, relatedness between nests and castes, and mating frequency of P. chinensis queens. These studies were conducted in South Carolina with 21 nests sampled over six locations.
The high variability inherent in microsatellite loci makes them ideal to gain insight on reproductive biology and ecological dynamics and can be used as an effective assay for documenting mating frequency in polygynous ants. Therefore, four Pachycondyla luteipes (Mayr) microsatellite loci were chosen for this study and were shown to be sufficiently informative in P. chinensis. The loci were polymorphic and unlinked but were not found to be in Hardy-Weinberg Equilibrium (HWE) due to heterozygote deficiency. The causes of HWE deviations were estimated to be a combination of biological factors rather than technical errors.
Allele frequencies reflected significant evidence of bottlenecked populations in at least two of the six locations but not on a global scale. Inbreeding coefficients, Fit and Fis, were high, suggesting a high level of nonrandom mating. Nests that were substantially separated by distance (> 5.0 km), were genetically differentiated. Pairwise Fst comparisons of individual nests resulted in nests sampled within a location being genetically similar. Number of reproductive migrants was calculated to be an average of 0.216 individuals between locations and 1.236 between nests per generation. Two locations indicated slight structure at the local level. Within the six locations, eight effective populations were detected globally.
The average intranest relatedness was lower than expected for true sisters (R = 0.579) as was the intralocation relatedness estimates. Nests within a location were not significantly correlated between distance and relatedness. Contradicting relatedness analyses, significant Isolation By Distance was found in two locations, meaning that neighboring nests in these locations were more genetically similar than distant ones. These results suggest that some populations of P. chinensis have unicolonial tendencies in regards to their relatedness. The relatedness of nestmate queens as well as queens to their nestmate workers was not significantly different from zero. Therefore, it is likely that queen contributions to offspring are not equal.
A procedure was developed to locate and remove the spermatheca and subsequently isolate the genomic DNA of male sperm from queens. Fifteen queens were used to estimate the proportion of polyandry which was calculated to be 0.683. Using allele frequency data, it was estimated that there was a 0.184% chance that double mating would be obscured due to two males having alleles identical to the queens, and a 38.4% risk that polyandry would be hidden if two males had identical alleles, thus appearing to be a single insemination. Based on these data, P. chinensis queens do mate with multiple males. However, given the small sample size and that polyandry was not detected at more than two microsatellite loci within an individual, quantification of mating frequency needs further study.
Tebeau, Andrew, "Reproductive strategies and colony relatedness in the invasive ponerine ant Pachycondyla chinensis (Emery)" (2009). All Theses. 626.