Fireflies in a new light: The diverse bacterial associations of northeastern American lampyrids

Fireflies are among the most charismatic insects on Earth due to their bioluminescent courtship behaviors, yet we know little about their microbiomes. As a group, fireflies offer diverse dietary and behavioral ecologies, providing a rich system to understand interactions between microbiome and ecology. In an attempt to better characterize firefly microbiomes, we tested the hypothesis that fireflies vary in their bacterial associations across tissues and species, with ecologically divergent fireflies harboring a different microbiome from their sister taxa. We measured bacterial density and profiled the microbiome of >590 fireflies from 12 species in the US using qPCR and 16S rRNA amplicon sequencing. We found that wild fireflies from species that consume food as adults (Photinus corruscus and Photuris spp.) had higher bacterial titers than most Photinus and Pyractomena species, which are not known to eat as adults. Members of the Pr. versicolor complex, which feed on other fireflies as adults, had consistently elevated bacterial titers in their guts and exposure to antibiotics reduced both their bacterial density and their survival rates. Firefly bacterial communities were generally dominated by members of the Mollicutes, with species-specific associations. The winter firefly Pn. corruscus, which is a day-active, nectar-feeding firefly, had drastically different bacterial associations, dominated by Entomoplasma and Rickettsiella, compared to other summer, night-active Photinus and Pyractomena species, which were commonly associated with Williamsoniiplasma species. This study paves the way to more research on the nature and functions of microbial symbioses across a range of host ecologies within the Lampyridae.