Biodiversity, Phylogeny, and Evolutionary Dynamics of Gall Midges on Japanese Beech Trees

The Japanese Archipelago harbors unique beech flora (<i>Fagus</i> L.; Fagaceae), with a parapatric distribution of two endemic species, <i>F. crenata</i> and <i>F. japonica</i>, upon which a diverse array of 34 types of leaf galls induced by gall midges (Diptera: Cecidomyiidae) has been documented. The inducers of most of these galls remain undescribed, and their phylogenetic relationships with known taxa are still poorly understood. In this study, we collected 29 types of leaf galls from the two Japanese <i>Fagus</i> species, including 6 previously unreported types, and sequenced the <i>cytochrome c oxidase subunit I</i> mitochondrial gene of the inducers to infer maximum-likelihood and Bayesian time-calibrated phylogenies. Our phylogenetic analyses revealed that the <i>Fagus</i>-feeding guild forms a monophyletic clade within the tribe Dasineurini, with <i>F. crenata-</i>feeding taxa occupying a basal position within the lineage. These taxa are closely related to the genera <i>Hartigiola</i> and <i>Mikiola</i> and have likely undergone adaptive radiation on the leaves of <i>F. crenata</i> and <i>F. japonica</i> in the ecologically segregated Japanese Archipelago since the Miocene period, accompanied by multiple host shifts between the two <i>Fagus</i> species and location shifts within their leaves.