Abstract
Adult males of the scarabaeid, Heptophylla picea MOTSCHULSKY, have flight muscles, whereas a portion of adult females loses their muscles. Geographic variation of the proportion of muscled females (PMF) in Japan was investigated with 54 population samples from diverse localities. Geographic trends in PMF variation were substantially different between the two areas ; muscled females were prevalent in eastern-central Hokkaido (PMF=100%), while in Oshima Peninsula, Honshu, and Shikoku, both types of females occurred and PMF varied irregularly from 0 to 100%. Based on the geographic trends, we hypothesize a possible process for the establishment of H. picea populations, including muscleless females, in the Japanese Archipelago, and discuss why the dimorphism is maintained in certain areas of its distribution.
