Date of Award
Doctor of Philosophy (PhD)
Microorganisms are now recognized to be integral components of the biology of many animal and plant taxa. These symbionts can play critical roles in host development, physiology, and in the mediation of ecological interactions among hosts. The study of insect-associated microbial symbionts is of particular interest, as insects comprise an enormous fraction of terrestrial biodiversity, provide important ecosystem services, and include destructive pests and disease vectors. However, symbiotic microbial functions are well-understood for only a limited set of insect taxa, and the broader ecological relevance of insect-microbe symbiosis is often unclear. Here, I describe four studies I undertook to investigate the structure and function of insect-associated microbiomes, with a particular emphasis on Lepidoptera (butterflies, moths, and their larvae). First, I conducted a comprehensive review of the literature pertaining to interactions between herbivorous insect gut microbes and the chemical compounds with which plants defend their tissues; these interactions may explain insect feeding patterns and diversification. Second, I found that antibiotic treatments, commonly administered to livestock, have unintended negative consequences: antibiotics retained in cattle dung affect the microbiome of dung beetles as well as modulate emissions of microbially produced greenhouse gases. Third, I investigated the composition and developmental dynamics of bacterial communities inhabiting a butterfly, finding that the butterfly microbiome undergoes a restructuring analogous to host metamorphosis. Fourth, I explored the gut microbiomes of a diversity of larval Lepidoptera, and found evidence for their generally transient nature. Collectively, these findings demonstrate that microbiomes can be highly diverse in form and function both within species and across major clades of hosts. They may also inform management practices, such as antibiotic use or pest control strategies.
Hammer, Tobin Jeremy, "Ecology and Evolution of Lepidoptera-Microbe Symbiosis" (2018). Ecology & Evolutionary Biology Graduate Theses & Dissertations. 114.