Presentation Type

Presentation

Faculty Mentor’s Full Name

Doug Emlen

Faculty Mentor’s Department

Division of Biological Sciences

Abstract

Male rhinoceros beetles (Trypoxylus dichotomus) wield an extreme weapon, a "pitchfork" shaped horn, that they use in battles with rival males over territories females visit to feed. The only places adult beetles can feed are at sap wounds on the sides of trees, and the biggest males with the largest weapons are best able to guard these feeding territories. As in other species with tusks, antlers, or horns, winning fights is expected to translate into winning opportunities to mate with females. However, female T. dichotomus routinely reject mating attempts by territorial males, forcing them to court by stridulatory 'singing'. Males sing courtship songs after they have mounted a female, by rubbing a ridge, on the dorsal surface of their abdomen, against a stippled surface on the underside tips of each elytron. I described, for the first time, the courtship songs of this species, and show that males alternate between two distinct song types: short bursts of harsh scraping (Song Type A) followed by gentler bouts of a smoother song that can persist for long periods of time (Song Type B). I used RAVEN software to characterize the properties of each type of song, and compared the songs of a sample of males, to test whether females might be able to assess the body size and/or physiological condition of a male through his song. I show that larger males produce lower frequency (Hz) songs than smaller males, and that males in better condition while courting (mass/body size) sing song type B at a faster rate (chirps/second). These results demonstrate that there are meaningful signals embedded within male courtship songs that females could use to assess the male. Future studies will be needed to test if and how females choose males in a system where female choice is traditionally overlooked.

Category

Life Sciences

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Courtship Singing in the Japanese Rhinoceros Beetle

Male rhinoceros beetles (Trypoxylus dichotomus) wield an extreme weapon, a "pitchfork" shaped horn, that they use in battles with rival males over territories females visit to feed. The only places adult beetles can feed are at sap wounds on the sides of trees, and the biggest males with the largest weapons are best able to guard these feeding territories. As in other species with tusks, antlers, or horns, winning fights is expected to translate into winning opportunities to mate with females. However, female T. dichotomus routinely reject mating attempts by territorial males, forcing them to court by stridulatory 'singing'. Males sing courtship songs after they have mounted a female, by rubbing a ridge, on the dorsal surface of their abdomen, against a stippled surface on the underside tips of each elytron. I described, for the first time, the courtship songs of this species, and show that males alternate between two distinct song types: short bursts of harsh scraping (Song Type A) followed by gentler bouts of a smoother song that can persist for long periods of time (Song Type B). I used RAVEN software to characterize the properties of each type of song, and compared the songs of a sample of males, to test whether females might be able to assess the body size and/or physiological condition of a male through his song. I show that larger males produce lower frequency (Hz) songs than smaller males, and that males in better condition while courting (mass/body size) sing song type B at a faster rate (chirps/second). These results demonstrate that there are meaningful signals embedded within male courtship songs that females could use to assess the male. Future studies will be needed to test if and how females choose males in a system where female choice is traditionally overlooked.