Abstract
Evolutionary transitions in animal diets often coincide with shifts in the microbiome, but the degree to which diet-microbiome feedbacks vary across host taxa and development is unresolved. We examined these potential feedbacks from the perspective of Lepidoptera (butterflies and moths), a diverse clade in which little is known about adult-stage microbial associations. With the exception of Heliconius butterflies, most lepidopteran adults are short-lived and either feed on simple substrates, like nectar, or do not feed at all. Heliconius consume pollen as adults, which provides amino acids and allows the butterflies to have an extended lifespan. Using 16S rRNA gene sequencing of 214 field-collected individuals, we found that adult passion-vine butterfly microbiomes exhibited a strong signal of host phylogeny, with a clear distinction between Heliconius and non-pollen-feeding relatives. This pattern was largely driven by differing relative abundances of bacterial phylotypes shared among host taxa, as opposed to the presence or absence of host-specific phylotypes. Using shotgun metagenomic sequencing, we also discovered trypanosomatids and microsporidia to be prevalent in butterfly guts, suggesting potential interactions with co-localized gut bacteria. Overall, we show that a major transition in adult-stage lepidopteran diet and life history coincides with a shift in microbiomes, and our work provides a foundation for future tests of microbiome function in adult butterflies.