Phylogeny And Biogeography Of Sinocyclocheilus Based On Mitochondrial Genomes

Genus Sinocyclocheilus,belonging to Cypriniformes,Cyprinidae,Barbinae,is an endemic fish to China,mainly distributed in karst areas which in the eastern of Qinghai-Tibet Plateau,including Yunnan Province,Guizhou Province,Guangxi Zhuang Autonomous Region,and Hubei Province.At present,there are 78 valid species,which is the largest fish of Cyprinidae in China.In this study,we collected specimens of Sinocyclocheilus extensively from Yunnan,Guizhou and Guangxi.The complete mitochondrial genome sequence was used to analyze the mitochondrial genome characteristics of the species,and based on the data of 13 protein-coding genes,phylogenetic relationships of the genus were constructed,and the species differentiation and biogeographic history of the genus in different regions were reconstructed.The results of this study are as follows:(1)A new species of Sinocyclocheilus from Xingyi City,Guizhou Province,China,namely Sinocyclocheilus xingyiensis sp.nov.,it was identified by combining the molecular and morphological characteristics approach.The new species became a member of the S.angularis group,can be distinguished from other species of Sinocyclocheilus by the following combination of characteristics: significant body budge along the junction of the back and behind the head;body completely covered in scales;eye diameter small(4.9%–7.4% of SL);two pairs of long barbels with maxillary barbel length 13.1%–19.9% of SL and rictal barbel length11.7%–19.2% of SL;pectoral fins long(19.2%–24.0% of SL),extending backward almost close to or reaching the insertion of pelvic fins;a straight lateral line,42–46 lateral line scales,10–13 scales above lateral line and 9–12 scales below;7(13–14)on outer(inner)side of the first gill arch;Total vertebrae 34–35,and pharyngeal teeth 2,3,4/4,3,2.The new species was the closest to S.flexuosdorsalis(the genetic distance of K2 P was 1.2%–1.4%),and is most similar to S.zhenfengensis in external morphological characteristics,but the morphology of the two species was clearly distinct from the new species.(2)The mitochondria of Sinocyclocheilus are a covalently closed circular double-stranded DNA molecule based on the characteristics analysis of the whole mitochondrial genome,including 37 genes and a control region(D-loop).The 37 genes included 13 protein-coding genes(PCGs),22 transfer RNA(t RNAs)and 2 ribosomal RNA(r RNAs).The gene sequence was consistent with the mitochondrial gene structure of other Cyprinidae fishes,with very conservative.The protein coding genes of Sinocyclocheilus have been strongly purification selection during its evolutionary process.(3)We constructed phylogenetic tree of the Sinocyclocheilus based on the data of 13 protein-coding genes of mitochondrial genes.Phylogenetic analysis showed that Sinocyclocheilus was a monophyletic group.Sinocyclocheilus could be divided into six Clades,namely,S.jii,S.angularis,S.tingi,S.cyphotergous,S.tianlinensis,and S.microphthalmus groups.The S.jii group is located at the bottom of the phylogenetic tree and it is the oldest group,next to S.tianlinensis group,S.microphthalmos groups,S.tingi group and S.cyphotergous group as sister groups.The phylogenetic problems of some Sinocyclocheilus of phylogenetic status unclear were solved.In addition,we support that S.jinxiensis is belong to Sinocyclocheilus instead of Pseudosinocyclocheilus.Meanwhile,we also found that there might be a phenomenon of different names in the genus Sinocyclocheilus,such as,S.ronganensis and S.pingshanensis,S.jiuxuensis and S.mashanensis,S.lingyunensis and S.luolouensis.However,the further morphological characteristics and molecular analysis are needed to confirm the proof.(4)The species of Sinocyclocheilus divergence time estimation and analyzed biogeographic processes using 13 protein coding data sets of mitochondria,to explore the species origin and evolutionary history of the genus.The results indicate that the common ancestor of the genus Sinocyclocheilus lived in the north-central region of Guangxi in the late Oligocene(25.84 Ma),and the primitive ancestral species spread and isolated to northeastern Guangxi,northwestern Guangxi and southwestern Guizhou,then spread to eastern Yunnan,and finally to north-central Guangxi and south-central Guizhou.After these ancestral populations reached their respective ranges,they diverged into new populations through diffusion isolation,forming the current distribution pattern.The evolution of genus Sinocyclocheilus is the result of isolation and diffusion interaction and interweaving,and founder-event speciation plays an important role in this process.At the same time,a series of geological events and water system changes caused by multiple uplifts of the Qinghai-Tibet Plateau,as well as climate change in the same period,played an important role in the distribution pattern and early diversified radiation of genus Sinocyclocheilus species.In conclusion,this study provides good data support for the study of the systematic evolution of fish of Sinocyclocheilus,to provide a basic basis for biogeography in the ecological conservation strategy of rare protected species of genus Sinocyclocheilus in China.