Population Genetics Research Of Widespread Coral Porites Lutea And Low Latitude Dominant Coral Pocillopora Verrucosa In The South China Sea

Population genetic diversity and genetic structure are important indicators for assessing coral environmental adaptability.In this paper,Porites lutea,a widespread massive coral species in the South China Sea,and Pocillopora verrucosa,a dominant branching coral species in the low latitude of the South China Sea,were selected as the research objects.The genetic structure and genetic differentiation at large spatial scales in the South China Sea of these two species were investigated by using two nuclear markers（ITS andβ-tubulin）and microsatellite markers.A total of 687 coral samples were analyzed,including368 P.lutea samples and 319 P.verrucosa samples,collected from Nansha islands（Sanjiao,Huayang,Xian’e and Xinyi）,Zhongsha islands（Huangyan）,Xisha islands（Beijiao,Qilianyu,Yongxing,Dongdao,Yuzhuo,Huaguang,Panshi and Langhua）,Hainan island（Dazhou,Luhuitou,Xidao,Wuzhizhou and Xipai）,Weizhou island and Daya bay（Xiaolajia and Yangmeikeng）.The sampling time is from May 2015 to June 2019.The specific scientific issues discussed include:1)Genetic diversity and genetic structure,including genetic differentiation,gene flow and population dynamics of P.lutea in the South China Sea;2)Genetic diversity and genetic structure,including genetic differentiation,gene flow and population dynamics of P.verrucosa in the South China Sea;3)Similarity and difference of published population genetics results among of representative corals in the South China Sea;4)Relationships between sea surface temperature,geographical distance,chlorophyll-a,turbidity and genetic differentiation of coral populations in the South China Sea.A total of 368 ITS sequences and 169β-tub sequences of P.lutea,250 ITS sequences,239β-tub sequences and 12 microsatellite loci data of P.verrucosa were obtained.MEGA,Dna SP,Arlequin,MIGRATE,NETWORK,Gen Al Ex,and Genepop were used for data analysis.The main results and conclusions are as follows:1.The population of P.lutea in the South China Sea belongs to a large collective population.The Daya bay population located in the northern margin of the South China Sea had low genetic diversity and high genetic differentiation;The genetic structure of Daya bay population was more unstable and more susceptible to human activities than that of other regions.Sea surface temperature（SST）dominated the genetic structure of P.lutea in the South China Sea.The results of genetic diversity and genetic structure of P.lutea in the South China Sea are as follows:1)The genetic diversity of P.lutea is high in the South China Sea,but lower in Daya bay;2)The bottleneck effect appeared in recent generations of P.lutea in the South China Sea,which may be caused by the general degradation of coral community in recent decades;3)The haplotype network showed that P.lutea in the South China Sea was derived from one ancestor;4)The large scale（about 1500 km）genetic homogeneity exists in the coral communities of P.lutea in the South China Sea,which may be due to their reproductive mode of ovulating,the periodic fluctuation of population size with glacial cycles and the expansion of population after the last glacial period;5)The genetic differentiation of Daya bay populations of P.lutea from others in the South China Sea may thus reflect the populations of P.lutea adaptation to lower winter temperature at the genetic level;6)There is a large gene flow（Nm>100）among other adjacent populations of P.lutea in the South China Sea,except for the small gene flow between Daya bay and Taiwan island.There was a symmetric gene flow from south-to-north in the South China Sea,this could be a reflection of global warming driving coral populations migrate in the south-to-north direction;7)SST dominated the genetic structure of P.lutea in the South China Sea,and geographical distance had relatively little effect on genetic differentiation.2.Populations of P.verrucosa in the South China Sea has moderate genetic diversity,and has a certain genetic potential in the context of global changes,but the high genetic differentiation between populations increases the risk of local degradation or extinction,especially Yongxing and Qilianyu populations;SST dominates the genetic structure of P.verrucosa in the South China Sea.The results of genetic diversity and genetic structure of P.verrucosa in the South China Sea are as follows:1)The genetic diversity of P.verrucosa in the South China Sea was moderate,but lower in Dazhou and Yongxing;2)The bottleneck effect appeared in recent generations of P.verrucosa in the South China Sea;3)The haplotype network showed that P.verrucosa in the South China Sea was derived from two ancestors,which may be linked to geographical isolation in the Pleistocene glacial period;4)AMOVA(Φ_ST=0.3375)and F_ST pairwise analysis results based onβ-tub showed that the populations were highly differentiated,with most F_ST values（21/45）>0.25,the reproductive mode of brooding planulae was an important factor contributing to high genetic differentiation among populations;5)Yongxing and Qilianyu populations of P.verrucosa may be affected by human activities and the outbreak of natural enemies,were significantly different from those in the Xisha area;6)There was a small gene flow（Nm<100）among populations of P.verrucosa in the South China Sea,except for some populations in Xisha islands（Qilianyu,Panshi and Yuzhuo）;7)Mantel test results showed that genetic differentiation among P.verrucosa populations was significantly and positively correlated with both mean SST and SST variance,and was not correlated with distance,chlorophyll-a,or turbidity.3.Based on the comparison of genetic characteristics among three known representative corals:P.lutea,P.verrucosa and T.peltata in the South China Sea,the following conclusions were drawn:1)The marginal populations at relatively high latitude had lower genetic diversity and higher genetic differentiation;2)SST is the main factor affecting the genetic structure of coral populations in the South China Sea;3)In the large spatial scale of the South China Sea,the genetic structure of different kinds of corals in the South China Sea was affected differently by geographical distance and reproductive pattern;4)Local factors,such as strong human activities or outbreaks of natural enemies,affect individual populations of corals and make them special in genetics;5)Based on the genetic results,it is suggested that the conservation priorities of reef-building corals in the South China Sea should be the relatively high latitude dominant species T.peltata,the low latitude dominant species P.verrucosa,which degrades faster,and the widespread massive coral species P.lutea.