Studies On Population Genetics Structure And Phylogeography Relationship Of Kandelia Obovata

Of all the mangrove, kandelia (rhizophoraceae) owns two species, namely Kandelia candel and K. obovata. Previously kandelia were all named into K. candel. And up to now, the scientific name is still misused in some studies. Actually, there is obvious difference in morphology, the number of chromosomes and physiological adaptation between the two species. K. candel mainly grows in the southern parts of South China Sea, while K. obovata in the northern parts of South China Sea. K. obovata mainly grows in China, which is also the distribution center of this species. It can be found in both tropical and subtropical regions, and is the most widely distributed mangrove plant in China. Its natural distribution pattern in China has provided good opportunities for us to study the effect of mangrove plant geographical isolation, propagules drift,shoreline changes and other issues. Besides, with the further deteriorated ecological environment for mangrove forests, it will give more theoretic basis to the scientific conservation of mangrove plants to study the genetic structure and phylogeography relationship of K. obovata. With the combined application of AFLP and SSR molecular marker and nuclear genes and chloroplast gene, studies have been made on K. obovata population growing in every province of China. The results proved that:1) Compared with the other populations, population in Ningde of Fujian features have quite obvious degree of differentiation, with evolutionarily significant unit. The population in Ningde of Fujian should be regarded as independent protection and management unit. The populations in Dongzhaigang of Hainan and Zhangjiangkou of Fujian are labeled with the most genetic diversity, and also the centers of origin. Therefore, they have been given special protection. The southern populations along Southeast coast of Chinese Mainland are more genetically diversified than those in the north. However, the populations in northern Taiwan are labeled with more genetic diversity than those in southern Taiwan.2) By speculation based on DIYABC, the middle and late Pleistocene arrive around140,000years ago, when populations respectively in the south and north of southeast coast of Chinese Mainland began to differentiate. And4,000years ago was the time when Taiwan populations began to differentiate in Chinese Mainland. The largest effective populations (N1=9840,95%CI=4490-9930) should go to the southern populations in the southeast coast of Chinese Mainland, followed by northern populations (N3=1970,95%CI=935-8880) in Chinese Mainland, and Taiwan populations (N2=354,95%CI=134-4920). The formation of the natural pattern of K. obovata results from the following reasons:they all originated from the southern populations of Chinese Mainland, however, as a result of the climate, the populations immigrated to the south to free from the climate influence during the ice age; during the interglacial period, the southern populations expanded along the northern shorelines to Yangtze River Delta and the Hangzhou Bay. When the ice age came once again, K. obovata moved back to northern Fujian as the temperature fell. During K. obovata expansion northward, influenced by bottleneck effect and founder effect, only a part of genes of the southern populations were inherited by the northern populations. In addition, as northern populations were easy to fluctuate, they performed more poorly in stability than the southern ones, so they featured less genetic diversity than the southern ones. The southern populations drifted northward following the western wave of Kuroshio and South China Sea currents, then settled down in northern Taiwan, and later expanded to southern Taiwan.3) Differentiation occurred unexceptionally in the8natural populations involved in the studies, which was likely to be caused by the change in shoreline, geographical isolation and the change in ecological environment. However, there exists gene flow between populations. Due to the difference in the degree of gene flow between populations, there is difference in degree of genetic structure difference. Because of the lower degree of gene flow, for example there is less gene flow between ND and other populations, ND most significantly distinguishes itself from other populations. Due to the frequent gene flow between ZJ, SZ, GX, DZG of the southern populations, there is little difference between populations. As to whether or not there was gene flow between Ryukyu and Japanese populations and the northern populations in Taiwan and southeast coast of the Chinese Mainland, it needs to be verified during later studies.4) For the man-made forests of K. obovata transplanted from the south to northern, their genetic diversity is not quite different from that of the original forests. However, there is obvious difference in genetic composition, which is the result of artificial seed selection. Therefore, artificial selection of nursery stock should be averted. The sampling error caused by artificial selection of nursery stock will reduce the genetic diversity, and lessen the size effective population. What’s more, when there is deviation in gene frequency of artificial forest, if there is gene flow with natural populations, gene frequency of natural populations will be changed.