Phylogeographic patterns of highland and lowland plant species in Japan

Abstract

As a result of ecological and historical factors, plant species occurring in mountainous regions often exhibit complex phylogeographical structure. The aim of this review is to identify the main phylogeographic patterns of plant species in the Japanese Archipelago, based on 63 previous studies; in particular, the intention is to examine the effects of mountains on these patterns. We classified species into three groups based on their distribution along altitudinal gradients: alpine and sub-alpine; montane; and lowland plants. Identified patterns were diverse, but we found particular ecological/historical constraints influencing the distribution of intra-population variation and contributing to clear genetic differentiation in alpine and sub-alpine and montane species. Many alpine and sub-alpine species harbored greater variation in the highlands of central Japan, and this was the case for dominant montane species in central and western Japan. These areas are considered to have acted as refugia during the last glacial maximum. Some other highland species even survived in small refugia in northern Japan. Genetic differentiation was regularly found between either side of 38°N latitude, between the Japan Sea and the Pacific Ocean sides of the country and on either side of the Itoiga-Shizuoka Tectonic Line. Unexpectedly, strong structure has rarely been found in lowland species. Based on the observed patterns, we discuss possible reasons for the discrepancies among phylogeographical structures of different species within the same groups. In addition, the phylogeographical patterns detected are compared with floristic structures described in classical biogeographical terms.