| Description |
Symbiotic relationships are common among bacteria and insects. Symbiotic relationships occur through two different methods: horizontal transmission and/or vertical transmission. Horizontal transmission occurs when the host organism acquires the symbiont from its external environment. Vertical transmission occurs when the parent organism transmits the symbiont to its offspring through germline cells. Vertical transmission is the least understood and is rarely observed in the natural environment. Current scientific data suggests that bacteria and insects established vertical transmitted symbiosis several millennia ago. However, it remains unclear how and why vertical transmission even originated. My thesis seeks to clarify and improve our current knowledge on these two questions. I began my thesis by selecting potential bacteria and insect symbiotic candidates. I selected the bacterium Sodalis praecaptivus because it is related to numerous insect symbionts. I selected the parasitic pigeon louse Columbicola columbae due to its specialized diet and an established symbiotic relationship with a Sodalis bacteria. The final insect I selected to use is the fruit fly Drosophila melanogaster, an insect that does not have a relationship with a Sodalis symbiont. The selected bacteria and two insect hosts provided an original and unique case study to attempt to establish vertical transmission. I applied a methodical, step-wise approach to answer my thesis. First, the insects iv had to be infected with S. praecaptivus. Second, the initial impacts of the infection had to be determined to be either positive or negative. Third, the infected insect had to be exposed to various environmental conditions to identify any potential symbiotic effects. Fourth, and final, the progeny of the infected hosts were studied to determine if the environmental conditions selected for vertical transmission. This step-wise approach allowed me to explore possible avenues on how and why vertical transmission originated. At the conclusion of my thesis research, I did not succeed in establishing vertical transmission. However, I did succeed in solving part of the original question of how and why vertical transmission is established. I concluded that it requires compatible organisms, both symbiont and host, and the unique environment to select for vertical transmission. |
