Horn Length Is the Determining Factor in the Outcomes of Escalated Fights Among Male Japanese Horned Beetles, <Emphasis Type="Italic">Allomyrina dichotoma</Emphasis> L. (Coleoptera: Scarabaeidae)
(1) Department of Biology, Tokyo Gakugei University, Nukui-kita 4-1-1, Koganei, Tokyo 184-8501, Japan
Abstract:
Male horn length in some horned beetles shows a sigmoidal relationship with body size. This has often been considered as the
reflection of alternative reproductive tactics of males based on body size. Large males should possess long horns to acquire
females through fights with other males using their horns, whereas small males do not require long horns because they usually
avoid intermale fights and adopt alternative tactics such as sneaking. This may lead to a prediction that horn length is a
reliable indicator of the fighting ability of the male. We examined the effects of both male horn length and body size of
Allomyrina dichotoma on the outcomes of escalated fights. Results indicate that male horn length was more important than body size in predicting
the outcomes of fight, and this may support the hypothesis that the evolution of the horn dimorphism in male horned beetles
is the result of different reproductive tactics.