Studies On The Comparative Molecular Phylogeography Of Three Gekko Species In Zhoushan Archipelago And Chinese Continent

Zhoushan archipelago locates in east of the China continent,and its islands are dotted in a large sea area.It has unique geographical environments which make it an ideal region for research of island biogeography and molecular phylogeography.In this paper,we selected the three geckos,Gekko subpalmatus,Gekko japonicus and Gekko hokouensis as organisms distributing in a wide range of Zhoushan Archipelago and China continent,to study the morphological and genetic differentiations among populations of continent and islands,to clarify the potential population genetic structures,and to analyze the population evolutionary history by application of phylogenetic and demographic analyses,and therefore,to discovery the relationship between population divergence and climatic and environmental changes.(1)Body size and island biogeographyWe have collected 330 gecko individuals from China continent and Zhoushan archipelago,including 93 individuals of G.subpalmatus from 19 localities,146 individuals of G.japonicus from 27 localities,91 individuals of G.hokouensis from 17 localities,a total of seven morphological characteristics including snout-vent length(SVL),head length(HL),head width(HW),arm length(AL),leg length(LL),distance between axillae(DBA),distance between iliac crests(DBI)were measured for each individual.The results showed that the species identification characteristics in the classification index for the three geckos were stable.All three species are lack of sexual dimorphism on SVL.Populations of G.subpalmatus are significant different on middle dorsal patches among three geographical areas from Sichuan,Fujian and Zhoushan Archipelago.The body size for each species represented by SVL and PC1 was larger for continent populations than that of island populations.Body size of island populations for different species has negative correlation coefficient with island area though the correlation relationship wasn't significant.Moreover,the body size of G.subpalmatus was significantly positively correlated with the shortest distance be-tween the island and continent,which might be correlated with the varied predation pressure for islands with different area.The morphological differentiation of middle dorsal line of G.subpalmatus was generally consistent with the population genetic structures of the species.(2)Prediction of potential geographic distribution based on MAXENT modelA total of 62 localities of G.subpalmatus(19),G.japonicus(27)and G.hokouensis(16)were obtained through new field investigation.A total of 122 localities points including G.subpalmatus(27),G.japonicus(74)and G.hokouensis(21)were obtained by literature review.Combined with 19 climatic and environmental variables,the MAXENT model was used to predict the current and historical distribution of the three geckos.The predicted results are highly reliable with AUC values ranged from 0.90 to1.00.The most warm monthly precipitation and the temperature difference between day and night are the main variables affecting the prediction of these species.The predicted distributions of geckos are basically consistent with the survey of field sampling investigation.All the potential historical distributions of the three geckos were affected by glacial and interglacial circulation.In the Last Glacial Maximum-LGM,the distribution of G.subpalmatus in central China(Hunan and Hubei)disappeared,but the potential distributing area in Sichuan basin and the east coast areas experienced expansion.By the middle of the holocene,the suitable area of G.subpalmatus in eastern coast area contracted and the suitable area of the Sichuan basin expanded to the south.The suitable area of G.japonicus was basically stable among three historical periods,but was affected by the last glacial maximum,and part of the suitable in central China(Hunan and Hubei)disappeared.During the LGM,the suitable distribution of G.hokouensis expanded towards the east of China.By the middle of holocene,the suitable area of Jiangxi had expanded and the suitable area of east coast had contracted.(3)Comparative molecular phylogeographyTwo mitochondrial DNA fragments including ND2 and COXI were sequenced for the geckos of G.subpalmatus,G.japonicus,G.hokouensis.Molecular phylogenetic analysis showed that there was not significant geographic genetic structures of G.japonicus and G.hokouensis.However,there three clades of G.subpalmatus in the phylogenetic trees,corresponding to Sichuan,Fujian and Zhoushan,respectively.The Sichuan basin branch of G.subpalmatus splitted earlies at 23 Ma,and this divergence is consistent with initial of extensive tectonic event occurred from Miocene to Pliocene(since approximately 23 Ma),which is cause of formation of the fragmentary fold belt in the southeastern Sichuan basin.The following divergence occurred between the Fujian branch and the Zhoushan branch at 20 Ma,which overlap the overall intensive uplift stage of Zhe-Min mountainous.A combined analysis including demographic and Bayesian Skyline analyses indicated that the island populations of three species experienced population expansion since 50,000 years ago under the influence of mid Würm glacial regression.The Sichuan population of G.subpalmatus experienced rapid shrinkage at 125,000 years ago due to global cooling.The genetic distance(0.1982-0.2240)among three branches of G.subpalmatus are very large which are quite close to the minimum genetic distance(0.2318-0.3559)among recognized gecko species.Combined with the differences in morphology,distribution and genetic differentiation,we believe that there might be cryptic species or subspecies within G.subpalmatus.