Although there is growing knowledge about host acquisition of gut microbes and how diet may impact the community structure, our understanding is limited by the lack of cultivable microbe manipulative experiments coupled with culture-independent sequencing. Monarch butterflies make an ideal, tractable system in which to investigate these questions because of its less diversified, microbial community, larval consumption of milkweed plants with medicinal properties, and the prevalence of a common, protozoan parasites. Medicinal milkweeds have higher concentrations of secondary chemicals, called cardenolides. Using cultivated bacteria from monarch eggs, larval host guts, and host food plants, we extracted, amplified, and sequenced bacterial 16S rDNA. If there is significant overlap of cultivable bacterial species between the sample types, we may be able to determine the source and transmission mode of the monarchs’ gut microbes. We also compared the identified cultivable bacteria to bacteria identified in previous culture-independent sequencing of larval guts fed on alternative host plants. By identifying cultivable bacterial species from different sample types, we may be able to determine the source and transmission mode of the monarchs’ gut microbes. We also compared the identified cultivable bacteria to bacteria identified in previous culture-independent sequencing of larval guts fed on alternative host plants.
Results/Conclusions
From the considerable overlap between the surface egg and plant samples, the surface egg bacteria may be transmitted from plants. The medicinal food plant had a higher bacterial richness and abundance than the non-medicinal plant, but did have four bacterial genera in common including: Staphylococcus spp., Bacillus spp., Paenibacillus spp., and Brevibacillus spp.. The higher bacterial abundance present in the medicinal plant was also present in the medicinally-fed gut of the monarchs. Surprisingly, the non-medicinal plant and the non-medicinally fed gut shared no bacteria. Most importantly, the results suggested that the guts reared on the two different milkweed diets are associated with different bacteria. This work will inform future experiments that will manipulate the gut microbial community of monarch butterflies to determine if bacterial species provide parasitic resistance.