Submission Date


Document Type

Paper- Restricted to Campus Access




Cory Straub

Committee Member

Anthony Lobo

Committee Member

Eric Takyi

Department Chair

Dale Cameron

External Reviewer

Clesson Higashi

Distinguished Honors

This paper has met the requirements for Distinguished Honors.

Project Description

Symbiosis between eukaryotes and prokaryotes is ubiquitous and has contributed to the origin of eukaryotes. Insects are the most abundant multicellular organisms and engage in symbiosis with diverse microbes, ranging from parasitism to mutualism. The pea aphid, Acyrthosiphon pisum, is an insect that harbors both obligate and facultative microbial symbionts. Hamiltonella defensa is a facultative bacterial symbiont known to provide protection to the pea aphid against the parasitoid wasp Aphidius ervi. In addition, H. defensa is known to provide aphids with protection against heat shock. Field data has been published demonstrating a rough positive correlation between H. defensa frequency and temperature throughout the year. We hypothesized that a possible explanation for this trend, in addition to thermo-protection, could be a cost to pea aphid reproduction for carrying H. defensa at colder temperatures. A lifetime fecundity experiment was performed involving three aphid genotypes divided into groups carrying and not carrying H. defensa at 12 and 20°C. Significantly higher fecundity was found in the groups carrying H. defensa at 12°C. The results of a second short-term experiment helped confirm this result. These findings were unexpected but not unprecedented, as at least one other study has shown pea aphid reproductive enhancement due to carrying H. defensa. Reproductive enhancement at cold temperatures may be caused by metabolic alterations involving only the pea aphid and H. defensa, or more complex dynamics involving stress on the host plant due to the cold.