2023 年 26 巻 3 号 p. 165-174
Elmomorphus beetles were recorded for the first time on Okinoerabu-jima Island in the Ryukyu Archipelago. Morphological examinations of the specimens clearly identified them as being Elmomorphus amamiensis. To date, based on the results of morphological classification and molecular phylogenetic analyses, two Japanese Elmomorphus beetles have been recorded; namely, Elmomorphus brevicornis and E. amamiensis. However, a third lineage was detected among them based on our genetic analyses. This third lineage was identified as being within the E. amamiensis populations of the Okinawa-jima and Kume-jima Islands and also in the Okinoerabu-jima Island populations and was newly discovered in this study. According to the analyses of all their nuclear and mitochondrial DNA, this third lineage did not constitute a monophyletic group with E. amamiensis of Amami-oshima Island (which is the type locality of this species), but rather formed a monophyletic group with E. brevicornis. These results suggested the following two possibilities: 1) the existence of a third distinct species, different from the other two species, 2) all three lineages together constitute one species as a whole and each lineage corresponds to a regional sub-clade within that species. In addition, the morphological characteristics that have been used to distinguish species/subspecies may themselves be problematic. Although it is not possible to come to a definitive conclusion as to which hypothesis is correct in this study, it has become clear that Elmomorphus beetles are an extremely significant species in discussions about the origin and phylogeographic history of the Ryukyu Archipelago.
