Establishment Of A New Genus And Hybridization Introgression Between A New Species And Two Labeonini Fishes

Labeonini(Cypriniformes: Cyprinidae)exhibit considerable diversity in their oromandibular structures,having undergone the greatest degree of evolutionary modifications to the morphology of the mouth and lips among all cyprinid fishes.Taxonomists often use oromandibular structures to identify these fishes,existing 54 genera of Labeonini.In 2016,we obtained 7 fish specimens,the characteristics of labeonini fish belonging to previously haven?t described species captured from the Hongshuihe River in Du?an County,Guangxi Province,southern China,were examined.This fish displays a distinct phenotype and genotype that cannot be confidently assigned to any known genus.Hence,we suggest that it represents a new genus and species,described herein as Lanlabeo duanensis,and carried out a series of studies on its taxonomy and hybridization.The main results including two parts were as follows:1.Establishment and identification of the new genus Lanlabeo.We conduct research on the identification of new species based on three aspects,including traditional morphology,skeletal and phylogeny.Lanlabeo is diagnosed from all other Labeonin genera by the following combination of characters: 1)frenum connecting upper jaw and lower lip at corner of the mouth;2)papillae densely scattered over ventral margin of rostral cap and regularly arranged;3)upper lip vestigial;4)rostral cap overlying upper jaw,with its posterior margin fimbriate;5)lower lip divided into two small lateral and translucent fleshy lobes and one central plate;6)median lobe of lower lip large,with papillae regularly arranged in many transverse rows.In the lower jaw of Lanlabeo,the dentary is transversely L-shaped in ventral view due to the anterior part forming a right-angle turn while the transverse branch is anterioposteriorly expanded.In contrast,the dentary is transversely L-shaped but with a narrow transverse branch in Rectoris and the anterior part of the dentary in Ptychidio extends anteriorly and does not form a turn.In addition,the postcleithrum of the pectoral girdle is slender and only ossified in the ventral part in Lanlabeo,whereas the postcleithrum is normally ossified in Rectoris.No ossified postcleithrum was observed in the examined Ptychidio specimens.Phylogenetic relationships based on the nuclear gene dataset strongly supported the validity and monophyly of Lanlabeo,has a sister group relationship with species of Ptychidio.The genetic distances(K2P)calculated based on the four nuclear genes examined between the new genus and other Labeonin genera ranged from 0.004 to 0.021.The genetic distance between Lanlabeo and Ptychidio is 0.006,which is within the range typical for inter-generic variation among labeonins.In summary,based on the morphological and osteological characters examined and molecular phylogenetic analyses performed that our results support the validity of the new genus.2.Introgression hybridization studies between Lanlabeo duanensis,Ptychidio jordani and Rectoris posehensis.In previous study,we used three samples performed phylogenetic analysis for identification the new genus,in this part of the study,five samples were added for the construction of phylogenetic trees.The combined data set of mitochondria genes(COI,CYTB,16 Sr RNA)and nuclear genes(RAG1,IRBP,EGR2 B,RH)was used.The results of mitochondrial gene and nuclear gene constitutive tree were diseordance,the reason for the inconsistency was the complex phylogenetic relationship between Lanlabeo duanensis,Ptychidio jordani and Rectoris posehensis.So we did the following analysis to understand the reason: 1)We built the Lanlabeo complex including Lanlabeo duanensis,Ptychidio jordani and Rectoris posehensis.Based on 66 individuals of the Lanlabeo complex plus related groups,the phylogenetic tree was constructed using the combined data set of mitochondrial gene and nuclear gene,respectively,showing that three individuals of Lanlabeo duanensis clustered with Ptychidio jordani and Rectoris posehensis in the mitochondrial gene tree.The results of the nuclear genetic construction revealed that six individuals of Lanlabeo duanensis were together located between Ptychidio jordani and Rectoris posehensis.We believe that hybridization may occur between Ptychidio jordani,Rectoris posehensis and Lanlabeo duanensis.2)A haplotype network map of the Lanlabeo complex was constructed based on the mitochondrial dataset and the nuclear gene RAG1,and the results were consistent with the phylogenetic analysis.3)The BPP analysis suggested to support the effectiveness of these three species by speciation probabilities = 1.0.4)JML analysis show that hybridization can explained the Cytonuclear diseordance rather than ILS(Incomplete lineage sorting).The observed genetic distances between Lanlabeo duanensis and Ptychidio jordani,Lanlabeo duanensis and Rectoris posehensis were less than 95% simulation value under ILS moldel(P = 0.0009-0.0071).5)The Beast inference the recent common ancestor differentiation of the Lanlabeo complex was in the early Pliocene(~4.72 Million years),After Speciation,due to the geological events the Lanlabeo complex may be distributed in the Sympatric.Hybridization of Ptychidio jordani,Rectoris posehensis and Lanlabeo duanensis can cause introgression.