Geographic Distribution of the Mayfly, Ephoron shigae in Japan, with Evidence of Geographic Parthenogenesis (Insecta: Ephemeroptera: Polymitarcyidae)

Abstract

The geographic distribution of Ephoron shigae in Japan was surveyed based on questionnaires and selected information from publications as well as collections. This species is distributed in rivers on Honshu, Shikoku and Kyushu from ca. 39°N to ca. 33°N in latitude. Temperature regimes from autumn to spring seem likely to be the main factor limiting distribution to this area. No or few males were found in some populations (unisexual populations), whereas many males as well as females were collected in some other populations (bisexual populations). The distributions of both populations broadly overlapped. The unisexual populations evidently reproduce parthenogenetically.