The effects of irrigation canals and roads as barriers to gene flow between Japanese brown frog (Rana japonica) breeding sites at a fine scale in a Satoyama landscape

Abstract

Paddy fields in the agricultural landscape have become alternative habitats for natural wetland species. Habitat degradation, including habitat loss and fragmentation, is a major threat to members of Amphibia, which is a good indicator species for the Satoyama landscape. Recently, linear artificial structures, such as roads and railways, were recognized as factors inhibiting amphibian population persistence. Thus, irrigation canals and cement-walled streams may also affect amphibian movement and dispersal in the rural agricultural landscape termed Satoyama, which is now the main habitat for lowland wetland amphibians. However, there is limited information on such effects. Here, we focused on the Japanese brown frog (Rana japonica), which is an indicator species of the ecosystem health of the Satoyama landscape, to investigate the effects of irrigation canals on population structure. The barrier effects of roads and irrigation canals on gene flow between breeding sites were evaluated. We constructed a resistance map of the limiting factors to gene flow based on land use and frog movement and tested for correlations between cost and genetic distances. The habitat resistance values alone were insufficient to explain the genetic distances among breeding sites. Thus, we hypothesize that irrigation canals and roads have barrier effects on gene flow among amphibians in the Japanese Satoyama landscape.