Predicting Genetic Demography of Rear-edge Populations of Hemerocallis Middendorffii: A Test for Climate Effects in Last Glacial Maximum and Holocene Optimum

Abstract

Background Quaternary climate changes significantly impacted population demography of temperate organisms by shifting their distribution. Notably, the rear-edge populations are considered to be more prone to these changes, but empirical studies showed the southernmost fragmented populations of Japanese woody plants to harbor high genetic diversities due to their southern glacial refugia origin. Therefore, the impacts of Holocene climate warming on rear-edge populations have been rarely demonstrated. For the better interpretation of genetic backgrounds of temperate plants, the association of paleodistributions under both icy and warm climates with species-specific demographic changes is required. A perennial daylily Hemerocallis middendorffii (Asphodelaceae) is widely distributed in temperate and cool-temperate zones of East Asia. In Japan, larger populations are found in central ranges, while few small populations survive on harsh rock walls in southernmost regions. We focused on these variable populations and aimed to predict the population demography in relation to past climate changes by statistically combining population genetics with paleodistribution modeling.Results EST-SSR analysis of 737 individuals from 41 populations revealed 6 regional population groups. Four groups widely dominating the northern–central ranges harbored high genetic diversity, whereas genetic divergence within the groups was low. However, two groups at the southwest edge were geographically and genetically isolated and showed the lowest genetic diversity. Estimated paleodistributions showed a decrease of suitable range during Holocene climate optimum in comparison with LGM, and a sole variable of habitat suitability in the Holocene optimum was able to predict genetic diversity across its range. Conclusions We concluded that habitat fragmentation and population decline in relation to the climate warming during the Holocene optimum and interspecific competition with woody plants resulted in genetic isolation and impoverishment of the rear-edge populations.