Date of Defense

Fall 10-1-2002

Department

Biological Sciences

First Advisor

DeWayne Shoemaker, Biology

Second Advisor

Todd Barkman, Biology

Third Advisor

David Cowan, Biology

Abstract

Walbachia are intracellular parasitic bacteria common in arthropods. Walbachia induce a number of phenotypes in their hosts including cytoplasmic incompatibility, thelytokous parthenogensis, geminization, and male killing. In the present study the author determined the distribution and frequency of Wolbachia infections in populations of the three fire ant species S. invicta, S. richteri, and S. quinquecuspis. Additionally, the author screened multiple individuals from twenty-nine monogyne colonies of S. invicta to determine the fidelity of the transmission rate of the bacteria from mother to offspring. Wolbachia infections occur commonly in individuals representing all three species throughout many parts of their native South American ranges, but are essentially nonesistent in North American populations of Solenopsis invicta and Solenopsis richteri. In the case of S. invicta, the proportion of infected individuals was quite variable among native populations, ranging from zero in the northern parts of its range to 93% in the more southern populations. The author's estimate of the fidelity of maternal transmission rates of Wolbachia in S. invicta was 99.3% (95% CI of 95.7% - 99.9%). This high rate of vertical transmission of Wolbachia suggests that the variation in infection frequencies within and across populations of S. invicta cannot be explained solely by incomplete transmission of Wolbachia. Three likely explanations are that Wolbachia are in the process of spreading through native populations of S. invicta, that there is a substantial fitness cost associated with harboring these bacteria, or that these bacteria have no effects on fire ants so that frequencies within populations are governed by genetic drift.

Access Setting

Honors Thesis-Campus Only

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