Multiple northern refugia for Asian sacred lotus, an aquatic plant with characteristics of ice-age endurance

Abstract

The effect of palaeoclimate on the distribution of aquatic plants is little known, although these plants typically have much broader geographical distributions than their terrestrial counterparts. We investigated the structure of genetic variation of chloroplast DNA in the Asian sacred lotus (Nelumbo nucifera Gaertn (Nelumbonaceae)) in 15 wild populations across China as well as in four populations from India, Japan and Thailand, to infer the refugia of this ancient plant during Quaternary climatic oscillations. We obtained 37 cpDNA haplotypes in 417 individuals from 19 populations. A moderate to high level of chloroplast genetic differentiation (GST = 0.547, NST = 0.691) and significant phylogeographic structure (NST > GST) were observed, suggesting a low level of recurrent seed-mediated gene flow among the populations. The results of AMOVA analysis also showed that more variation was partitioned among (71%) than within populations (29%). The phylogenetic relationships for the recovered haplotypes showed that haplotypes of wild lotus in north-eastern China significantly diverged from those distributed in central and southern regions of China. A high level of haplotype diversity, rather than reduced genetic diversity, in north-eastern China indicated multiple refugia in northern China during the Quaternary glaciations. Lotus plants have the following two characteristics that facilitated survival through Quaternary glaciations: seeds buried in mud remain viable for thousands of years, and self-heating flowers can reproduce in cold temperatures.