PS 40-110
Monarch butterfly immunity within an ecological context: Effects of medicinal food plants on midgut microbial composition
Hosts have evolved a range of mechanisms to protect themselves against parasites that are a large threat to their fitness. In addition to canonical immune responses, hosts can utilize biotic factors, or living species, in their environment for additional protection. Monarch butterfly (Danaus plexippus) larvae actively consume milkweeds (Asclepias spp.) that contain secondary chemical compounds, named cardenolides, which reduce parasite infection and virulence. The common protozoan parasite Ophryocystis elektroscirrha infects monarch larvae by traversing the midgut wall which contains microbial communities that could play a crucial role in immunity. Medicinal milkweeds could impact the parasite by either: 1) directly interfering with parasite infection; or 2) indirectly altering the host gut microbiota to an anti-parasitic state. To test these alternative hypotheses, we combine culture and culture-independent methods to characterize the composition of the monarch caterpillar midgut microbiota. Infected and uninfected caterpillars were reared on medicinal and non-medicinal milkweed species. We dissected the second instar larvae midgut, and extracted and amplified DNA. The 16S rRNA gene was cloned and sequenced. We identified the dominant, cultivable bacteria strains which will allow further testing of the extent at which milkweed cardenolides confer protection.
Results/Conclusions
If milkweeds exert their protective effects through modulating microbial communities in the gut, we expect to find that the microbiota are more similar for caterpillars reared on species within a group (medicinal versus non-medicinal) than for caterpillars reared on milkweed species of different groups. Our preliminary data indicate monarch caterpillars raised on medicinal and non-medicinal milkweed diets have simple midgut microbiota.