Diet modulation of host gut microbiota and its impact on disease resistance in monarch butterflies
Hosts have evolved a range of mechanisms to protect themselves against parasites that are a large threat to their fitness. These defenses can extend beyond intrinsic host immunity and incorporate aspects of the environment in which host and parasite interact. Monarch butterfly (Danaus plexippus) larvae actively consume milkweeds (Asclepias spp.) that contain secondary chemical compounds, named cardenolides, which reduce parasite infection and virulence. Here, we use monarch butterflies and their protozoan parasites (Ophryocystis elektroscirrha) to study diet’s interaction with the gut microbiota and natural parasite infection. To test if medicinal milkweeds alter monarch gut microbial communities, I compared the gut communities of monarch caterpillars reared on one non-medicinal and one medicinal milkweed species. We dissected the second instar larvae midgut, and extracted and amplified DNA. The 16S rRNA gene was sequenced. We identified the dominant, cultivable and non-cultivable bacterial genera which will allow further testing of the extent at which milkweed cardenolides confer protection.
My preliminary comparison of gut bacterial communities of second instar caterpillars fed on alternative milkweed diets revealed that the midgut bacterial community composition of uninfected caterpillars significantly differs based on the host plant (medicinal vs. non-medicinal milkweed) on which the larvae feed, though bacterial community composition does show substantial variation between individuals within a given host plant treatment.