Inferring future changes in gene flow under climate change in riverscapes

Global climate change poses a significant threat to the habitat connectivity of cold-water-adapted organisms, leading to species extinctions. Because gene flow is itself a functional connectivity among wild populations, if gene flow is modeled by landscape variables, changes in population connectivity could be predicted. In this study, using a model-based riverscape genetics technique and a hydrological model to estimate water temperature, we inferred the determinants of and future changes in gene flow of the fluvial sculpin Cottus nozawae in the upstream section of the Sorachi River, Hokkaido, Japan. As a result of model selection, stream order, water temperature, slope, and distance were detected as landscape variables affecting the strength of gene flow in each stream section. In particular, the trend of greater gene flow in sections with higher stream order and lower temperature fluctuations or summer water temperatures was pronounced. The map from the model showed that gene flow is overall prevented in small tributaries in the southern area, where spring-fed environments are less prevalent. Estimating future changes in gene flow using future water temperature predictions, genetic connectivity was predicted to decrease dramatically until the end of the 21st century under IPCC representative concentration pathway scenario 8.5 (RCP8.5).