A Preliminary Study On The Structure And Function Of Intestinal Flora In Juvenile Yangtze Finless Porpoises(neophocaena Asiaeorientalis Asiaeorientalis)

As gut microbiome is critical for host’s nutrient absorption and immune defense,it has been regarded as one of the important study areas in conservation biology and has been expected to provide essential insights for endangered animals’ health management and conservation decisions.The Yangtze finless porpoise(Neophocaena asiaeorientalis asiaeorientalis,YFP)is the sole freshwater population of the genus Neophocaena,and is endemic to the middle and lower reaches of the Yangtze River,including its two adjoining lakes(Poyang Lake and Dongting Lake).By the end of 2017,the population of YFPs has declined to approximately 1012 individuals,resulting in the unoptimistic conservation situation and the urgent need of conservation biological studies.However,gut microbial studies of YFPs are underestimated at present.As the juvenile period is the key stage for the initial colonization of gut microbiome,and gut microbiome in the juvenile period plays a decisive role in the host’s immune system establishment and organs’ maturation.Investigating the gut microbial structure and dynamics of juvenile YFPs can provide basis for further exploring the gut microbial physiology function,homeostasis and disease prevention of YFPs.Therefore,this thesis explored the diversity,composition,influencing factors and potential functions of juvenile YFPs.The main results are as follows:(1)We explored the gut microbial diversity,composition and potential functions of juvenile YFPs from three different developmental stages,including newborn(0～1 month-old),babyhood(1～6 month-old)and infancy(6～24 month-old).Among the 39 genera shared by three developmental stages,Clostridium sensu stricto＿1,Clostridium sensu stricto＿2 and Paraclostridium occupied more than 62%.Even though the alpha diversity indices in three developmental stages showed no significant differences(P < 0.05),the babyhood period(during the food conversion period)harbored a higher gut bacterial diversity.A further analysis showed that the relative abundance of Sarcina,Paraclostridium and Paeniclostridium increased with age.And the relative abundance of Pseudomonas,Aeromonas,Escherichia and Cetobacterium peaked in the babyhood period.Moreover,predicted functions including ‘energy metabolism’and ‘epithelial cell signaling in Helicobacter pylori infection’ increased with age.This could be correlated with the growth rate in response to food conversions,and the ingested fish may increase the Helicobacter pylori infections.(2)We compared gut microbiota of YFPs that were exclusively breast-fed or formula-fed.Between different groups,alpha diversity was significantly higher in breast-fed group that formula-fed group(P < 0.05).The Enterococcus were significantly lower in breast-fed group that they were in formula-fed group(P < 0.05).Additionally,most predicted functions including ‘starch and sucrose metabolism’,‘quorum sensing’ and ‘amino acid biosynthesis’ were significant higher in breast-fed group than the formula-fed group(P < 0.05).This may imply that the formula-feeding style may influence animal’s physical functions and health conditions by impacting its gut microbial structure and function.(3)We investigated the differences of gut microbiota from neonatal YFPs and its congeneric marine Indo-Pacific finless porpoises(N.phocaenoides;IFPs).The dominant phylum and genus of YFPs were Firmicutes(65.25%)and Clostridium sensu stricto 1(40.67%),while the dominant phylum and genus of IFPs were Proteobacteria(57.78%)and Vibrio(27.85%).Additionally,predicted functions including global and overview maps,carbohydrate metabolism,and replication and repair were more abundant in YFPs than those in IFPs;however,predicted functions including cellular community-prokaryotes,membrane transport,and energy metabolism were less abundant in YFPs than those in IFPs.In both YFPs and IFPs,lower microbial diversity and smaller proportion of predicted signal transduction were found in the rectal samples than those in other gut regions(foregut,midgut and hindgut),while the function of glycan biosynthesis and metabolism were predicted higher in the rectal fecal samples compared with that in other gut regions.This study expands our knowledge on the gut microbial community composition and diversity of neonatal finless porpoises,and enriches the scientific data on the gut microbiome of cetaceans in the early life stage.