Species Differentiation And Ecological Adaptation Of Three Schizothoracinae Fish Species In Gansu Province

The studies on speciation and population differentiation are important to understand the mechanism of speciation and conservation of biodiversity.Schizopygopsis pylzovi,Gymnocypris chilianensis and Schizopygopsis kialingensis,belonging to subfamily Schizothoracinae,are widely distributed in the 3 river systems from Gansu province.In the past study,the phylogenetic relationship between these 3 Schizothoracinae fishes were complex.Few reports have been published on genetic differentiation among different populations as well.In the present study,we extended sampling ranges and employed mitochondrial DNA Cyt b gene for better understanding on speciation and population genetic differentiation of 3 Schizothoracinae fishes.Meanwhile,we studied trophic niche differentiation of these Schizothoracinae fishes using stable isotope analysis.Finally,in order to comprehend species composition and assembly rules of communities.We then paid attention to the phylogenetic structure of fish community and its mechanism of community construction in the 3 continental rivers from Gansu province.The following are the main results:1.In the present study,294 Schizothoracinae specimens,including Schizopygopsis pylzovi,Gymnocypris chilianensis and Schizopygopsis kialingensis,were collected from 8sampling sites belonging to the Yangtze River,the Yellow River and continental rivers in Gansu Province.We employed mitochondrial DNA Cyt b gene as molecular marker to perform the phylogenetic analyses,genetic diversity and population differentiation analysis of the 3 Schizothoracinae fishes.Phylogenetic analyses for all haplotypes based on NJ and BI methods revealed that S.pylzovi was clustered as monophyletic group.However,S.kialingensis was clustered into a clad with G.chilianensis.This result suggests the two species are under early stage of speciation.Therefore,we assumed that S.kialingensis was originated from some populations of G.chilianensis.After speciation of S.kialingensis,the rest of G.chilianensis populations were not clustered as monophyletic group but as paraphyletic group in these two species.2.Twenty-three haplotypes were identified for 70 individuals of S.pylzovi from 3rivers,28 haplotypes were identified for 132 individuals of G.chilianensis from 5 rivers and 13 haplotypes for 92 individuals of S.kialingensis from 3 rivers.Total haplotype diversity and nucleotide diversity of S.pylzovi were 0.917 and 0.00310,respectively,while 0.819 and 0.00982 for G.chilianensis,0.706 and 0.00233 for S.kialingensis.No haplotypes were shared between two different species and significant population differentiation were detected between geographic populations showing that geographic isolation has a significant impact on these Schizothoracinae fishes,and adaptive differentiation as well.Hence,it should be treated as evolutionary significant units for different populations in conservation management.3.Six Schizothoracinae species including the three mentioned above and other three sympatric species were collected in 8 sites from Gansu Province to understand trophic niche differentiation employing stable isotope analysis?SIA?.Trophic level,?¹³C and?¹⁵N value of G.chilianensis was the highest in these 6 Schizothoracinae species.The trophic niche width of G.chilianensis,S.pylzovi and S.kialingensis ranged relatively wider than other species.The fundamental niche overlapped sharply within G.chilianensis,S.pylzovi and Gymnodiptychus pachycheilus.In the spatial scale,we found difference in trophic niche between different populations for each species.However,sympatric species showed different results of interactions between species.In Huangyang River,trophic niche overlap indicated strong competition between sympatric species.On the contrary,in the Shimen reservoir,there was no trophic niche overlaps that we assumed competition resulted in trophic differentiation between these sympatric species.Finally,we found the trophic niche was not restricted by the conservation of phelogeny using mantel test between genetic distance and SIA characters.4.Fish samples from 3 continental rivers?Shule River,Hei River,Shiyang River?in Gansu province were collected to explore the mechanism of fish community assembly using the method of phylogenetic community structure analysis.The results showed that the phylogenetic structure of fish communities in 3 of the 10 sampling sites were clustering,indicating habitat filtration as the mechanism of community assembly.Among them,the community assembly of 2 sampling sites were alpine habitat filtration,and one sampling site was a reservoir formed by human disturbance as a special environment filtration.There was no phylogenetic structure of the community at one sampling site because of only one species collected.The community phylogenetic structure in the other6 sampling sites was overdispersion and the competition exclusion among species worked as the community assembly mechanism.In this study,fish conservation strategies were discussed for different locations,which had different community assembly mechanism.We suggested that environmental protection should be the priority to some places where the community assembly mechanism was habitat filtration,while the introduction of alien species should be prohibited to maintain the stability of the fish community for sites where the community assembly mechanism was competition exclusion.