Population Structure of Wild Schizothorax kozlovi in the Upper Yangtze River Based on mtDNA and Stable Isotopes, and Their Relationship with Ambient Temperature

Abstract

Schizothorax kozlovi, as an endemic and vulnerable fish of the upper Yangtze River in China, faces many threats. In order to expose the population structure of wild S. kozlovi, the carbon and oxygen isotopic ratios in the otoliths, and the gene sequences of two common mitochondrial markers (Cytb and COI) were investigated in four sampling locations, and then their relationship with ambient temperature was further investigated. In general, it exhibits limited geographic population structuring of S. kozlovi in the upper Yangtze River by both mtDNA and stable isotopes. The values of otolith stable isotope ratios varied from −15.30‰ to −12.37‰ for δ18O and from −10.10‰ to −6.13‰ for δ13C. Significant relationships were revealed between stable isotope ratios and specific mean monthly water temperature variables (from November to March), indicating low temperature effect on otolith stable isotope ratios. Haplotype diversity and nucleotide diversity were 0.928 and 0.00778, both exhibiting high levels. A median-joining haplotype network indicated a mixture of geographical distribution but exhibited two distinct haplotype lineages (Clade I and Clade II). AMOVA detected that the higher percentage of genetic variance was within sampling locations (96.94%) and between two haplotype lineages (72.82%). Most FST values between sampling locations showed small levels of genetic differentiation except the differentiation between population SJ (Sanjiangkou) and JP (Jinping). Therefore, two haplotype lineages and population JP of S. kozlovi in the upper Yangtze River are suggested as three management units for conservation due to their moderate-to-great genetic differentiation and isolated habitat.

Characterization of the Complete Mitochondrial Genome of Schizothorax kozlovi (Cypriniformes, Cyprinidae, Schizothorax) and Insights into the Phylogenetic Relationships of Schizothorax

“…Therefore, research on and attention to the biology of S. kozlovi are urgently needed for sustainable resource conservation. Previously, researchers have conducted studies on growth, reproduction, diet, population, and diversity [ 15 , 17 , 18 , 19 , 20 , 21 ]. But there has been little focus on the characterization of the mitochondrial genome and phylogenetic analysis for S. kozlovi .…”

“…For example, Heckel [30] recommend that the Schizothorax can be divided into three groups based on the shape of the head and the morphology of the mouth; Chen et al [31] suggested that the Schizothorax should be classified into two subgenera on the basis of the presence or absence of keratin at the anterior edge of the jaw. Moreover, researchers have previously used single mitochondrial gene such as Cyt b or COI to determine phylogenetic relationships for species among Schizothorax, which may lead to one-sided and biased conclusions [21,22,32]. Within this context, it is necessary to unite multiple makers from genomes to investigate the taxonomic and phylogenetic relationships for Schizothorax.…”