| Hainan Island is located at the south of our country and in a tropical region at low latitudes.It belongs to a tropical monsoon climate,surrounded by the sea and has no connection with the freshwater of the mainland and belongs to a typical island ecosystem.The island is rich in natural resources and is one of the hotspots in biodiversity research in China.The freshwater planarian(Tricladida,Platyhelminthes)plays an important role in the phylogeny of animals.It is also a model organism in many fields such as Genetics,Development,Evolutionary biology,and Regeneration biology,but there are few researches on freshwater planarian on the Hainan Island.The freshwater planarian on the Hainan Island was systematically studied in this study.The objectives of our study are:(1)to investigate the distribution of freshwater planarian in Hainan Island;(2)to analyze the chromosomes and karyotypes of freshwater planarian in Hainan Island by a chromosome analysis system;(3)to analyze the molecular phylogeny of freshwater planaria in Hainan Island and its relationship with the formation of geographical pattern in Hainan Island with the help of ribosomal and mitochondrial marker genes.The chromosomes and karyotypes of Dugesia sp.from 29 localities on the Hainan Island were studied by air drying method or resuspension method.18SrDNA、28SrDNA、mtDNACytb、mtDNACOI sequence of the Dugesia sp.from 35 localities on the Hainan Island were sequenced through PCR amplification.The phylogenetic tree was constructed by NJ method and Bayesian method,and its relationship with geography was discussed.The freshwater planarians from 40 localities on the Hainan Island were analyzed in this study.All the freshwater planarians found on the island were Dugesia sp.,and no other genus were found on the island.The freshwater planarians in the central mountain range are the most densely distributed,followed by the western mountains,however the southern and northern of the island are less distributed.The chromosomes and karyotype analysis showed that:the cardinal number of chromosome of Dugesia sp.from 29 localities on the Hainan Island is 8,which 18 localities are diploid(2n = 2x = 16),2 localities are triploid(2n=3x=24)and 9 localities are mixoploid of diploid and triploid.Among them,the Dugesia sp.of 18 localities such as Mangwang,MiaocunshangA,MiaocunshangB,Limufengzhufeng,Jinkuangpubu,Guanyuanerqiao,Yinggezuixiayou,Maodancun,Guanglan,Yapaicun,Maonaocun,Chongmentoucun,Shenpingqiao,Yongzhongcun,Guimenguan,Baodaocun,Baihualling and Diaoluoshan are diploid,and their karyotype formula is 2n = 2x = 16 = 16m.The Dugesia sp.of 9 localities such as Miaocunxiayou,Mingfenggu,Shipubaitanqiao,Tianchi,Yulingu,Sanxingjian,Wuzhishanxia,Jiuwentang and Yanghuyiqiao are mixoploid of diploid and triploid,and their karyotype formula is 2n = 2x = 16 = 16m or 2n = 3x = 24 = 24m,which 4 localities(Miaocunxiayou,Mingfenggu,Yulingu and Shipubaitanqiao)are mainly triploid,whereas 5 localities(Tianchi,Sanxingjian,Wuzhishanxia,Jiuwentang and Yanghuyiqiao)are mainly diploid.The Dugesia sp.of Wuzhishanshang and Heilanqiao are triploid(2n = 3x = 24 = 24m).Hainan Island is located in the tropical regions with low latitude.The temperature of the whole island is relatively high relative to the inland area.The annual average temperature is 22.5℃-25.6℃,but the central mountainous area is a relatively low temperature environment,furthermore the temperature changes little all the year round.The environment is relatively stable,so the degree of chromosome variation in this area is relatively small and simple.There are only diploid,triploid and its mixed ploidy,and most of them are centrometacentric chromosomes.Most karyotype types are 1B or 2B karyotypes and little of them are 1A and 2A karyotypes.The results of karyotype asymmetry plot and the comparison of karyotypes of Dugesia sp.showed that:Dugesia sp.of Limufengzhufeng is special,both its average arm ratio and the ratio of chromosome length(L/S)are high so that far distributed in the upper right of the scattered plot,and its degree of karyotype asymmetry is the highest,whereas the evolution of the other localities of Dugesia is similar..The phylogenetic analysis of Dugesia sp.on Hainan Island showed that:the 18SrDNA of the four marker genes selected in this paper is not reliable,so its interference is excluded.The genetic distance between the Dugesia sp.from 35 localities on the Hainan Island is obviously differentiated.The genetic distance between most of them is very close between 0.000-0.100,but the genetic distance between some Dugesia sp.localities such as Limufeng(LMF),Jiuwentang(JWT),Qixianling(QXL),Baodaocun(BDC)and other localities is up to a long genetic distance,which indicates that there should be more than one species of Dugesia sp.in Hainan Island,and the specific species classification still needs to be further explored.Based on the paleogeographic information and phylogenetic analysis of Hainan Island,a variety of geological movements make the diffusion of freshwater Dugesia in Hainan Island more complicated. |
