A phylogenomic analysis of lichen-feeding tiger moths uncovers evolutionary origins of host chemical sequestration

Host species utilize a variety of defenses to deter feeding, including secondary chemicals. Some phytophagous insects have evolved tolerance to these chemical defenses, and can sequester secondary defense compounds for use against their own predators and parasitoids. While numerous studies have examined plant-insect interactions, little is known about lichen-insect interactions. Our study focused on reconstructing the evolution of lichen phenolic sequestration in the tiger moth tribe Lithosiini (Lepidoptera: Erebidae: Arctiinae), the most diverse lineage of lichen-feeding moths, with 3000 described species. We built an RNA-Seq dataset and examined the adult metabolome for the presence of lichen-derived phenolics. Using the transcriptomic dataset, we recover a well-resolved phylogeny of the Lithosiini, and determine that the metabolomes within species are more similar than those among species. Results from an initial ancestral state reconstruction suggest that the ability to sequester phenolics produced by a single chemical pathway preceded generalist sequestration of phenolics produced by multiple chemical pathways. We conclude that phenolics are consistently and selectively sequestered within Lithosiini. Furthermore, sequestration of compounds from a single chemical pathway may represent a synapomorphy of the tribe, and the ability to sequester phenolics produced by multiple pathways arose later. These findings expand on our understanding of the interactions between Lepidoptera and their lichen hosts.