A phylogenetics and morphology-based investigation of tymbal evolution in Arctiinae (Lepidoptera: Erebidae)

Moths in the subfamily Arctiinae possess the ability to produce ultrasonic clicks as a defense strategy against their primary predator, bats. Because many arctiines sequester toxic chemicals from their larval host plants, these ultrasonic clicks primarily serve to communicate toxicity to bats, but some arctiine lineages have secondarily evolved to use sound in courtship. In Arctiinae, sound is produced using two paired metathoracic organs called tymbals, that flex inward to produce sound. A tymbal is typically a convex bubble-like region of the exoskeleton that has a bumpy strip running down the side, known as a striated band, but tymbal morphology is highly variable between species with some even lacking a functional tymbal altogether. I aim to document the tymbal morphology of representative species from across Arctiinae and map them onto the most recent arctiine phylogeny. I photographed tymbal organs from approximately 85 species in 46 genera and used ImageJ to quantify tymbal shape, length of the striated band and other characteristics. I then used principal component analysis (PCA) to examine overall tymbal variation within this sample. While my results are preliminary, the study will improve our understanding of the ancestral state of arctiine tymbals and how the diversity seen today developed over evolutionary time.