Dimorphism of both head and prothoracic horn morphologies in male Copris acutidens (Coleoptera: Scarabaeoidea)

Allometric scaling of male horn morphologies of Copris acutidens, including the head and prothoracic horns, was analyzed. The analyses of scaling relationships indicated a discontinuous increase in head horn length and prothoracic horn height but a linear increase in prothoracic horn length relative to body size. The different results for length and height of the prothoracic horn suggest that the height is functionally more important for ensuring mates in the nests. Furthermore, both the head and prothoracic horns were dimorphic, and this characteristic was not found in the scarabaeoid beetle Onthophagus. Similarity in the switch point values for the head and prothoracic horns suggests that the dimorphism of the two kinds of horns may result from the same developmental threshold mechanism. The analyses of allometry in male Copris acutidens (Scarabaeoidea) indicated a discontinuous increase in head horn length and prothoracic horn height, but a linear increase in prothoracic horn length. This study found that both head and prothoracic horns were dimorphic in the genus Copris. This finding is different from that previously reported in the genus Onthophagus. © 2016 The Entomological Society of Japan.