Study On The Formation History And Genetic Differentiation Of Small Mammalian Fauna In Hainan Island

Island has been considered to be an excellent natural laboratory for the study of biological evolution.As an important part of the India-Burma biodiversity hotspots,Hainan Island is rich in species diversity.Hainan Island has experienced multiple major geological events and paleoclimatic events in the history,and the surrounding areas have complex and diverse geographical features,providing a good model for studying biological evolution.However,there have been limited phylogeographic studies of this area.It is of great biological significance to reveal the phylogeographic relationships of the species on the island,as well as the degree and time of their genetic divergence,and to further explore their possible biogeographic origins and mechanism of genetic divergence.Based on the principles and methods of molecular phylogeography,and using mitochondrial genes and nuclear genes as molecular markers,this study systematically investigated the phylogenetic relationships between nine small mammals on Hainan Island and the surrounding continental species,as well as their degree of genetic divergence and divergence time.In addition,taking into account the paleogeological events,paleoclimate and animal physiological and ecological habits,etc.,the mechanism of genetic divergence of these species was discussed.According to the present distribution and phylogenetic topology of these species,we concluded that there were three potential origin partterns:Leopoldamys edwardsi,Rattus losea,Rattus nitidus,Mus caroli,Dremomys pyrrhomerus and Callosciurus erythraeus originated from China mainland;Lepus hainanus and Tamiops maritimus originated from Indo-China Peninsula;Mogera insularis originated from Taiwan island.It is noteworthy that one reversed dispersal patterns were discovered in this study:the reversed dispersal of L.peguensis from Hainan Island to Indo-China Peninsula.This dispersal pattern is meaningful for phylogenetic study of Hainan Island in the future.The Hainan clades of L.edwardsi,D.pyrrhomerus and M.insularis were detected by high degree of genetic differentiation(mean K2P>5%);The Hainan clades of C.erythraeus,T.maritimus and L.hainanus showed moderate degree of genetic differentiation(mean K2P 2.8?4.1%);The Hainan clades of Rattus nitidus,Rattus losea and Mus caroli showed low degree of genetic differentiation(mean K2P<1.7%).The genetic distance of M.insularis,D.pyrrhomerus and L.edwardsi relative to their nominate subspecies were all greater than 5%,which was a criterion for species delimitation in rodents.We suggested that they should be elevated to species level,so the mammal species diversity of Hainan Island was underestimated.Our relaxed molecular clock analysis suggests that there are three time scales of divergence within these nine small mammals:(1)D.pyrrhomerus,M.insular is and L.edwardsi in Hainan Island diverged from their sister clades approximately in late Pliocene?early Pleistocene(2.66Mya,2.83Mya and 2.36Mya,respectively).Geological event in northern Hainan Island may promote the diversification of the three species;(2)L.hainanus,C.erythraeus and T.maritimus diverged from their sister clades approximately in early Pleistocene(0.95?1.29 Mya).The sea-level fluctuations in early Pleistocene may promote the diversification of the three species;(3)R.nitidus,R.losea,and M.caroli diverged from their sister clades approximately in Middle Pleistocene(0.86?0.53Mya).The sea-level fluctuations may promote the diversification of the three species in Hainan island.In conclusion,geological event and climatic shifts are the most important factor in the diversification of the nine small mammals.The results of our divergence time and K2P distance divide these nine species into three groups.And we found that this divide consistently correlate with their physiological and ecological traits.The low dispersal capabilities of M.insularis may contribut to the largest divergence.D.pyrrhomerus and L.edwardsi also showed the high divergence which may be resulted from their strict forestdwelling trait.In the ice age,the land bridge between the Hainan Island and mainland can not develop the forest for it to disperse,so the gene exchange was prohibited.On the contrary,L.hainanus,T.maritimus and C.erythraeus were not strict forestdwelling species,the Hainan clades had the moderate divergence.R.losea,R.nitidus and M.caroli were all generalist species,their Hainan clades had the low divergence.