| The family Turdidae are widely distributed passerine birds,with 65 species currently distributed in South Asia,Central Asia and North America,Eurasia and Africa.Although it is distributed worldwide;however,the phylogenetic relationship of most Turdidae is uncertain.Only a few superspecies groups have established phylogenetic relationships.The ability of an individual to recognize and eliminate pathogens is fundamental to their survival.The major histocompatibility complex in vertebrates is encoded by the genes which are and expressed almost all cells of the body,which can recognize various antigens and participate in immune response against antigen.MHC class I molecules can bind to protein peptides on the surface of intracellular viruses,MHC class II molecules recognize and present extracellular antigens.Because major histocompatibility complex(MHC)genes play a crucial role in the vertebrate immune system,they have been extensively studied in many taxa.When a population has abundant MHC gene variation and high genetic diversity,it may imply that it has strong environmental adaptability and more capable to face the challenges.The diversity of major histocompatibility complex class I and II genes in wildlife populations depends on local or global environmental selection pressures and gene flow.In this study,we conducted the following studies for the first time:1)The genetic diversity of MHC class I genes was assessed in four species of Turdidae family distributed in northern China.77 MHC class I gene sequences were successfully isolated from 80 individuals,including 47 functional gene sequences and 30 pseudogene sequences.On an average,we sequenced 25 clones per individual,the results showed that individuals had 2-7 MHC I gene sequences,which indicated that genus Turdus had more than one MHC I site.The results of the analysis showed that the genetic diversity of the MHC I gene was strong,and its PBR and nonPBR domains had different selection patterns.The polymorphic loci of alleles vary widely,ranging from 58-70(total loci 291).In addition,shared alleles are significant across species sampled species due to recent speciation or convergent evolution in species.Phylogenetic analysis showed that MHC I alleles clustered together in thrushes,but not in other passerines.Polymorphisms in the MHC I gene are critical for long-term survival of thrushes.2)Biologist frequently identify the species from their distinctive structure assisted with the valuation with specimens in reference collections such as those held in galleries or by comparison with their external morphological characteristics.We have contextualized the methods of species identification and elaborated the means by which species relation with other species is measured.Here,we conclusively summarized the application of different molecular markers used in species identification and population genetic diversity of Turdidae family.These methods include ND2 and CO1 genes in mitochondrial DNA,microsatellite loci markers,introgression investigations.Microscopic and gross morphological properties of feathers,hairs,beaks and claws of samples are very useful tools for identification of species.In our study;we have utilized Brazilian quantitative morphological characteristics for species identification in thrushes which were tail length,wing length,toe length,claw length and tarsus.We found,that female Turdus atrogularis in early winter are very similar to Turdus ruficollis but tail color was other than redlacks.In addition,Turdus eunomus are still more confused Turdus naumanni.Therefore,the morphological characteristics also indicate that the four species of thrushes involved in this study are closely related.An overall there was certain deviation in distinguishing birds’ species based on the morphological characteristics of birds.3)The genetic diversity of exon 2 of the MHC confused than Turdus naumanni although they have more pronounced color differences.II B gene of four thrush species distributed in northern China was evaluated.Fifty-three MHC II B exon 2 alleles were isolated in 48 individuals,and we obtain 1.04 alleles per individual.In comparison,the nucleotide diversity(π)of the second exon of the MHC II B allele of the Turdus atrogularis thrush was higher than that of the Turdus naumanni(1.97:0.167).The mean nucleotide difference also varied between Turdus atrogularis and Turdus naumanni(22.81:17.04)respectivily.The Turdus naumanni and the Turdus eunomus shared 2 alleles,and the Turdus atrogularis and the Turdus ruficollis shared 3 alleles.Due to the different evolutionary history of each domain of this gene,we perform the selection analysis respectively.The results showed that the non-synonymous substitution of the Turdus atrogularis was significantly higher than that of the synonymous substitution(0.821),and the d N/ds in the antigen-binding region was more obvious.Overall,the Turdus naumanni has 13 positively selected codons in this gene,the Turdus eunomus has 7,the Turdus ruficollis has 11,and the Turdus atrogularis has 9,which is less than that of other passerines and humans.In addition,allelic crossspecies phenomena are evident due to recent speciation or convergent evolution.The phylogenetic relationship of MHC II B genes in Turdidae presents intermingling of alleles across sampled species.Our study signifies a useful means for the description of evolutionary related MHC dissimilarity across the bird’s population with significant conservational apprehensions.In our investigation,the molecular methods along with sequence data collected from public domain in this research should add to a well considerate the evolutionary importance along with the conservation inferences of the MHC in birds of Turdidae family.Given that major histocompatibility complex genes may conclusively define the parasite and pathogen resistance our investigations may also help in conservation of genetic diversity in sampled species.Our study suggests that MHCI & MHCIIB genes as valuable tool for the characterization of evolutionary relevant differences across the population of birds with high conservational concerns. |
