Mandible dimorphism in males of a stag beetle, Prosopocoilus dissimilis okinawanus (Coleoptera: Lucanidae)

抄録

The dimorphism of weapon size in a stag beetle, Prosopocoilus dissimilis okinawanus Nomura was examined. The relationship between weapon size and body size became curvilinear when head length was included as a part of body size. However, when it was used as a part of weapon size a sigmoid relationship was obtained. Males could not be separated into two groups when nine traits were analyzed using principal component analysis (PCA). However, when the angle of the mandible (AN) was used in addition to the nine traits, males could be separated into two distinct groups (i.e. S and L types). When the size of each of the nine traits was plotted against the AN, males of the S type could be separated into two sub-groups in all combinations (i.e. S1 and S2 groups). The relationship between body size and weapon size showed that weapon size increased with body size in a quadratic manner in the S type, whereas it increased in a diminishing quadratic manner with body size in the L type. The difference in the relationship between weapon size and body size in the S and L types is discussed in relation to their combat behaviors.