Biogeographic Studies On The Genus Platycrater(Hydrangeaceae)Endmic To East China And South Japan

Platycrater arguta Sieb. et Zucc (Hydrangeaceae) is an East Asia endemic genus disjuncted distribution in East China and South Japan. It rarely distributed in Zhejiang, Fujian and Jiangxi province in China, and Central Honshu, Kyushu and Shikoku in Japan. The two varieties within the genus, Platycrater arguta var. sinensis H. Hara and Platycrater arguta var. arguta, distributed in China and Japan respectively. After a preliminary survey of specimen, field sampling and habitat observation across the known distribution plots, population genetics study of14Platycrater arguta populations (including314individuals) were carried out using multiple molecular markers (cpDNA psbA-trnH and trnD-trnE regions, nrDNA ITS, single-copy nuclear gene Tpi and seven nSSRs). We integrated the genetic diversity and population structure of Platycrater arguta with the addition of Ecological Niche Modeling analysis to interpret allopatric speciation evolution of Platycrater arguta and population demographic history after speciation. ESUs and ex-situ conservation strategies was also discussed. Major results are shown below:1. Chloroplast DNA analysisHigh level of genetic diversity (RT=4.02, hτ=0.88, πT=0.00475) and significant population genetic structure (NST=0.857> GST=0.787) was observed within Platycrater arguta populations. Strong genetic differentiation (FST=0.915) of the two Platycrater arguta varieties results from geographic isolation. Japan haplotypes are paraphyletic nested by China haplotypes. TCS haplotype analysis shows no shared haplotypes between China and Japan populations. A paraphyletic relationship between China and Japan haplotypes were observed from the phylogenetic analysis. MDA analysis of China and Japan population did not refuse the expansion model (P>0.05).The divergence time of cpDNA lineages are earlier than the Last Glacial Maximum (0.89Ma). Significant expansion was observed in Japan population after the divergence of the two varieties.2. Nuclear marker analysis based on nrDNA ITS and single-copy nuclear gene TpiIn total,33/31haplotypes were detected in the ITS and Tpi marker respectively. High level of nucleotide diversity and haplotype diversity were observed at the genus level (Tpi:h=0.92, rc=0.02; ITS:h=0.96, rc=0.04). No shared haplotypes were found for both nuclear sequence markers. ITS phylogenetic analysis supports the status of the two varieties.3. Microsatellite marker diversity and population genetic structureTwelve Platycrater arguta specific microsatellite markers were developed using two different strategies. Seven of them, with higher genetic diversity, were used in the population scanning. In total,220alleles were detected. China population (Na=66) has a higher average allele than Japan (Na=43). High level of genetic diversity was also observed in nSSRs data (Hr=0.89). STRUCTURE analysis demonstrate that when K=7, China populations were grouped into five clusters, while genetic admixture pattern were observed in Japan populations; when K=7, C7and Japan populations are homology.4. Isolation with Migration analysis based on multiple markersIMa analysis based on cpDNA, ITS, Tpi and SSR markers shows the divergence time of the two varieties are0.89Ma. Compare to Japan population (NA=24.45×104), a higher effective population size were observed in China population (NA=46.02×104).5. Ecological Niche ModelingAll54distribution records of Platycrater were included in the ENM analysis. Ecological Niche Modeling simulated the potential distribution area of Platycrater arguta in present day, LGM and LIG. The simulations well support the scenario that Platycrater arguta populations contracted and survived in the refuges during the LGM and then expanded after the glaciation. Variable contribution analyses show that BIO18(Precipitation warmest quarter) has the highest relative contribution of the19environmental variables to the maxent model under both two LGM models (CCSM:36.9%; MIROC:48.2%). This result is consistent with our field observation.In conclusion, the two varieties of Platycrater in East China and South Japan divergence earlier than LGM and survived on the East and South side of East China Sea. Allopatric speciation induced by climate change in early Quaternary isolated the Platycrater arguta ancestral population. The occurrence of East China Sea landbridge during the LGM did not facilitate bidirectional migration of Platycrater arguta after their divergence. Incomplete lineage sorting may play an important role during the evolution of Platycrater (especially for Platycrater arguta var. sinensis). Two refuges were detected in South Japan in the North and South region respectively. Each refuge possesses its own genetic components, a second contact happened in the central region of Japan when the two refuge population expansion during the post glacial period. At the same time, multiple evolutionary units were identified based on our study; related conservation strategies were also discussed.