COLLABORATIVE RESEARCH: Multimodal signaling in rhinoceros beetles

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This study seeks to understand biodiversity by focusing on animal weapons and courtship displays, which often diversify more rapidly than other traits. Male rhinoceros beetles wield a giant, pitchfork-shaped horn on their head that they use in battles between rival males over feeding territories visited by females. Males with the longest horns win, in part because horn length accurately reflects body size and fighting ability of males - it is an honest signal of male quality. Prior work by the investigators revealed that winning fights is not enough, however. Even after battling to hold a territory, males must still spend hours each night "singing" to females using a novel file on their wing covers that they rub against a plate on their abdomen, and they produce blends of scents in their waxy outer cuticle that appear to communicate male body size and nutritional state. This study will explore the link between male condition and both song and scent signals, examine female preferences for these signals, and characterize the diversification of this suite of courtship signals across the range of the species. How do females discriminate among males, and why do they ignore the obvious signal of male quality (the horn)? The investigators will also work with the Gonzaga department of dance to design performances inspired by animal behavior, develop an interactive exhibit on insect songs for the Missoula Insectarium, and design interactive online curricula for K-16 students through the University of Denver to share information about beetles with the public. Prior work on the Japanese rhinoceros beetle, Trypoxylus dichotomus, a heavily weaponed species characterized by a textbook resource defense mating system, led the investigators to suspect that these beetles show elements of lekking behavior. Females are reluctant to mate with resident males guarding feeding territories despite those males consistently being among the largest, longest-horned individuals in the population. Using a combination of laboratory manipulation experiments and field observation and perturbations, this study will rigorously characterize stridulatory song and cuticular hydrocarbon (CHC) profile signals in rhinoceros beetles (Aim 1), and evaluate their importance to female mate choice (Aim 2) and male rival assessment during contests (Aim 3). In addition, this study will compare song dialects and CHC profiles across the range of this species (Aim 4), to contrast the relative rates of evolution of agonistic and mate-choice signals. Finally, they will perform a quantitative trait locus mapping study of adjacent, genetically similar but phenotypically divergent populations, combining the resulting linkage maps with a re-sequenced reference genome, and FST 'outlier' results from a prior PoolSeq study of the same populations, to delve into the genetic architecture of this suite of multimodal signal traits.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.