Morphological Variation And Population Genetic Structure Of Chinese Bean Crab (Arcotheres Sinensis) In Coastal China

The phylogeography of marine organisms shows that the distribution pattern of marine organisms may be closely related to the glacial-interglacial cycles from the end of Miocene to the middle of Pleistocene,and gradually formed the Pleistocene sea level fluctuation hypothesis and glacial refuge hypothesis.It has been reported that the geographical distribution pattern of marine organisms is also affected by geographical distance,habitat discontinuity,as well as the ecological mechanism of marine organisms themselves.The characteristics of marine environment in different sea areas,such as ocean current,marine frontal system,surface temperature and salinity,may affect the geographical distribution pattern of marine organisms.In this study,the method of combining traditional morphology and molecular biology was used to explore the geographical distribution pattern and formation mechanism of Arcotheres sinensis and to reveal the genetic structure and historical dynamics of those populations.The results are as follows:1.A total of 9 morphological variable indicators of 8 populations 226 individuals were calculated and the results showed the body size of A.sinensis did not show a gradual differentiation along the latitude gradient.ANOVA analysis of all relative morphological measurements indicating that there were very significant differences among populations.However,further multiple comparative analysis showed that such geographical differences did not present certain rules.The results of relative morphometric cluster analysis showed that there was no obvious regional geographic structure in the morphology of the eight geographic populations.2.The sequences of 163 mtDNA COI and 149 nrDNA H3+ITS of A.sinensis were determined to analyze genetic diversity,neutral test,phylogeny and population history.The result showed that a total of 20 haplotypes were defined,and the mean nucleotide diversity of COI was 0.018,and the mean haplotype diversity was 0.622.The F_STof the 8 populations ranged from 0.00 to 0.95,and F_STin Beihai,Zhuhai was greater than 0.8 which reached significant differentiation level(P<0.01).The AMOVA test showed that 91.01%of the genetic differences existed between groups,and 8.81%within the groups.A total of 33 haplotypes were defined by H3+ITS.The overall haplotype diversity was 0.784 and the mean nucleotide diversity was 0.010.The Structure results showed that the population of A.sinensis could be divided into two genetic clusters:South China Sea(SCS),East China Sea(ECS)+Yellow Sea(YS).The results of phylogenetic tree based on two molecular markers showed that there was a large genetic differentiation between SCS and ECS+YS,and a clear phylogeographic structure was formed.3.The most recent common ancestor time of all populations was 0.948 Ma.The population haplotypes in the YS+ECS began to diverge at about 0.225 Ma,and the population haplotypes in the SCS began to diverge at about 0.217 Ma.During the Pleistocene Ice Age,the decrease of sea level may lead to the differentiation of A.sinensis populations in three marginal seas.In the SCS and ECS,the composition of ocean current circulation is complex,and the pea crab may move a certain distance with the China Coastal Current and Kuroshio Current in the SCS and ECS,and produce gene flow in different geographical regions,while the Changjiang Diluted Water had no significant effect on the geographical distribution pattern of A.sinensis.4.The results of the study on population differentiation of A.sinensis by using molecular methods and morphological methods are inconsistent,which may be related to many factors.Due to the different sampling time,host and the different growth and development status of A.sinensis,the conclusions based on morphological measurement data could not fully reflect the pattern of genetic diversity.