Gene diversity and geographic differentiation in mitochondrial DNA of the Genji firefly, Luciola cruciata (Coleoptera: Lampyridae)

The Genji firefly, Luciola cruciata, is divided into two ecological types, the fast-flash and slow-flash types, on the basis of the interflash interval of mate-seeking males. To evaluate the evolutionary origin of the two types, 62 populations were examined by restriction fragment length polymorphism analysis of the mitochondrial cytochrome oxidase (CO) II gene. As a result, 19 haplotypes were detected, and their distributions were indigenous to local areas. Phylogenetic trees constructed from sequence comparison of the haplotypes revealed three major clades (I, II, and III). The boundary of haplotypes between clades I and II is approximately concordant with the geological structure of the Japanese Islands, which is a great rupture zone called the Fossa Magna, and the distribution of haplotypes in clades III and I-II corresponds to the Kyushu and Honshu-Shikoku Islands, respectively. The results suggest a vicariant scenario in which current L. cruciata diversity would have arisen from phylogenetic separations subsequent to the formation process of the Japanese Islands based on the molecular clock. The CO II gene trees also suggested that the fast-flash type should be considered an ancestral form, while the slow-flash type would be a derived one. The divergence time between the slow- and the fast-flash types is estimated to be about 4.6 to 2.0 mya (the Pliocene epoch).