Speciation Of Fish Genus Rhinogobio

Rhinogobio,an endemic genus to China,belongs to Gobioninae,Cyprinidae, Cypriniformes;which consists of 5 species:R.typus Bleeker,R.cylindricus Günther, R.ventralis Sauvage et Darbry,R.hunanensis Tang and R.nasutus(Kessler).By using 3 species R.typus Bleeker,R.cylindricus Günther and R.ventralis Sauvage et Darbry as the subjects,the persent study aims to investigate speciation of this genus. The followings are the main conclusions.1.The study investigates phylogeny,speciation and population history of species in Rhinogobio by using Cyt b gene and intron I of S7 ribosomal protein gene as the molecular markers:ⅰ260 Cyt b gene sequences(81 from R.typus,72 from R.cylindricus and 107 from R.ventralis)and 36 sequences of intron I of S7 ribosomal protein gene(10 from R.typus,14 from R.cylindricus and 12 from R.ventralis)were obtained.Two samples of R.cylindricus share common haplotyes of Cyt b gene with R.typus.It is suggested that the two samples of R.cylindricus should be the offsprings of R.typus and R.cylindricus as the result of introgressive hybridization.ⅱThe phylogenetic relationship is constructed using neighbor-joining method based on Cyt b gene and intron I of S7 ribosomal protein gene.R.typus and R. cylindricus are more closely related to each other than to R.ventralis.R.ventralis is more distal-related to the other two species.ⅲR.ventralis and the ancestor of R.typus and R.cylindricus differentiated in late Miocene about 6.19 million years ago,and have become perfectly reproductively isolated from R.typus and R.cylindricus.ⅳR.typus and R.cylindricus differentiated in late Pliocene about 2.285 million years ago.R.typus and R.cylindricus are definitely 'good species' at present,but they still introgressively hybridized to some degree.Their introgressive hybridization consists of the leakage of the alleles from R.typus gene pool to R.cylindricus.ⅴR.typus,R.cylindricus and R.ventralis experienced population expansion about 87084,42304 and 48560 generations ago respectively.2.Thirteen meristic characters and 24 measurable characteristics of 179 samples (65 from R.typus,42 from R.cylindricus and 72 from R.ventralis)were analyzed to investigate the morphological differences and character evolution of species in Rhinogobio,using the methods of principal component analysis,cluster analysis and making clustered bar charts:ⅰThe morphological differences among R.typus,R.cylindricus and R.ventralis are specified perspicuously.The most distinguishable characters of R.ventralis are the number of scales above the lateral line,scales below the lateral line and the ratio of dorsal fin length to head length.The ratio of caudal depth to body length and the ratio of eye diameter to body length are the most effective characters to distinguish R.typus and R.cylindricus.The number of scales above the lateral line ranges from 7.0 to 8.5 with an average of 7.25±0.40 in R.ventralis;The number of scales above the lateral line in R.typus and R.cylindricus both ranges from 6.0 to 7.0 with an average of 6.03±0.16 and 6.03±0.16 respectively.The number of scales below the lateral line ranges from 6.0 to 8.0 with an average of 6.42±0.48 in R.ventralis;the number of scales below the lateral line ranges from 5.0 to 6.0 with an average of 5.26±0.30 in R. cylindricus;and in R.typus,the number of scales below the lateral line ranges from 4.0 to 5.5 with an average of 4.68±0.39.The ratio of dorsal fin length to head length is above 1 in R.ventralis;but in R.typus and R.cylindricus,the ratio is below 1.The ratio of caudal depth to body length in R.typus ranges from 0.065 to 0.080 with an average of 0.071±0.003;but in R.cylindricus,the ratio ranges from 0.081 to 0.096 with an average of 0.087±0.003.The ratio of eye diameter to body length in R.typus ranges from 0.039 to 0.056 with an average of 0.046±0.003;but in R.cylindricus,the ratio ranges from 0.026 to 0.035 with an average of 0.031±0.002.ⅱThere is an evolutionary trend in the genus Rhinogobio towards more lateral line scales,less scales above and below the lateral line,less predorsal scales,less ramose pectoral fin rays,a more columned body figure,a lower body and caudal depth,larger eyes,a longer snout,shorter fins,narrower dorsal and anal fin base length and a more anterior anus. ⅲThe differentiation of morphological characters is the result of adaption evolution.R.ventralis with stronger caudal peduncal and fins,smaller eyes and a shorter snout is adapted to fast-flowing tuibid rivers and R.typus and R.cylindricus are adapted to slow-flowing clear habitats.ⅳThe morphological results support the conclusions of molecular analysis about the speciation of the genus Rhinogobio.