Molecular Phylogenetic Relationships And Selection Pressures Among Sinocyclocheilus Species Based On Five Immune Gene Sequences

The fish genus Sinocyclocheilus is endemic to China and belongs to subfamliy Barbinae,famliy Cypriniade,and order Cypriniformes.This fish genus is closely related to cave and has unique characteristics of rich species diversity,strong species differentiation and wide population distribution.The phylogenetic development in the Sinocyclocheilus is not fully solved because there are some controversies in the study based on morphology method and molecular markers method.Meanwhile,many researches indicate that innate immune genes can recognize foreign pathogens and participate in the immune response process by activating pattern recognition receptors,interferon and other cytokines and that under positive selection pressure,species or individuals can evolve to have more advantages in reproduction and survival.However,there are few studies on the selection pressure of immune genes in Sinocyclocheilus,so the analysis of selection pressure based on immune gene sequences are helpful to understand the adaptive evolution of SinocyclocheiluIn this paper,we use PCR-DS method to collect 16 species of Sinocyclocheilus's IFIH1 gene encoding area part of the sequences(effective length 327 bp),22 species of Sinocyclocheilus's IRF-2 gene encoding area part of the sequences(effective length 123 bp),16 species of Sinocyclocheilus's NODI gene encoding area part of the sequences(effective length 174 bp),22 species of Sinocyclocheilus's TLR4 gene encoding area part of the sequence(effective length 450)and 23 species of Sinocyclocheilus's TLR7 gene encoding area part of the sequences(effective lengt 504 bp).By analyzing the merged data set,we do the research about the molecular phylogenetic relationships and selection pressures among Sinocyclocheilu species.This research will provide not only guidance for the protection of Sinocyclocheilus,but also have potential research value for the genetic diversity of Sinocyclocheilus.The research results are as follows:First,from the phylogenetic tree constructed by 5 immune-related genes,we found that"The subgroup Jiao" of Sinocyclocheilus were earlier than "The subgroup Tuobei" of Sinocyclocheilus on their phylogenetic differentiation,which is consistent with the related previous reports.Second,the phylogenetic tree constructed by TLR4 and TLR7 associated gene displaye that the Sinocyclocheilus distributed in Yunnan is located at the top of the phylogenetic tree,which indicates that the species distributed in Yunnan in this study are relatively late in differentiation.Third,the phylogenetic tree constructed by TLR4 and TLR7 associated gene illustrates that S.microphthalmus and S.maculatus get together in a branch.Moreover,the result further proves the genetic relationship of two species.Finally,we performed selection pressure analysis through the dataset which was associated by TLR4 and TLR7 of 22 species of Sinocylocheilus.The result implyed that the selection pressure is positive in Sinocylocheilus.Among them,the positive sites 86P,149G,251R and 291E were greater than 0.90.In addition,the results showed that the immune gene sequences of TLR4 and TLR7 also evolved adaptatively in the evolutionary process of the Sinocylocheilus.