Abstract
Headwaters, the streams that make up the beginnings of rivers, are unique components of catchments as they usually support a taxonomically and ecologically unique fauna. However, since headwaters are generally narrow and have a fluctuating course, they have received little attention from ecologists, and their benthic fauna, including insects, is poorly studied. This paper focuses on an endemic Japanese mayfly Dipteromimus tipuliformis, which has possibly very limited dispersal ability, and is restricted to headwaters. Its ecological relationships (its dispersal ability) and genetic variation (genetic distance within and between populations in the mitochondrial 16S rRNA gene sequences) were discussed, and compared with some other mayfly species (ephemerid mayflies, and other related mayflies) living in other water systems. Dipteromimus tipuliformis showed greater inter-population genetic distances than those of any other of the mayfly species examined.
