Mitochondrial DNA variability to explore the relationship complexity of Schizothoracine (Teleostei: Cyprinidae)

Abstract

Despite numerous studies on the taxonomy of a highly complex group of schizothoracine (snow trouts), with over five recognized species from Kashmir, India (Schizothorax niger, Schizothorax esocinus, Schizothorax plagiostomus, Schizothorax curvifrons and Schizothorax labiatus) based on traditional morphological data, the relationships between these species is poorly understood and the taxonomic validity is still under debate. To resolve the evolutionary relationships among these species, we sequenced mitochondrial fragments, including 16Sr RNA, Cytb and the D-loop. Separate analyses of 16S and Cytb showed intermixing of the species and 16S was found more conserved than Cytb. The D-loop was found highly variable and showed length variation between and within species. Length variation was observed in di-nucleotide (TA)n microsatellite repeats with a variable number of repeat units (n = 7-14) that did not show heteroplasmy. Central conserved sequence blocks (CSBs) in D-loop sequences were found comparable to other vertebrate species. All phylogenetic reconstructions recovered the focal taxa as a monophyletic clade within the schizothoracines. Analyses with combined mitochondrial data sets showed close genetic relationships of all the five species. In addition to a close relationship between S. niger and S. curvifrons, two distinct groupings of S. ecoscinus and S. plagiostomus were supported by all the analyses. This study gives an insight into molecular phylogeny of the species and improves our understanding of historical and taxonomic relationships derived from morphological and ecological studies.

Integrative approach for validation of six important fish species inhabiting River Poonch of north-west Himalayan region (India)

“…In the current study, two mitochondrial genes were used to validate the fish species using a binary approach, such as phenotypic and genotypic data in order to resolve the ambiguity among six important fish species of the Poonch River. A combined analysis of mitochondrial loci mostly agrees with morpho taxonomical studies (Silas, 1960;Ahmad et al, 2014), indicating that the integrative method could effectively resolve uncertainty in the identification and understanding of morphological relationships even with a low sample size. Therefore, molecular phylogenies and phenotypic studies can be compared using standard methods to come up with a robust conclusion.…”

“…No work has been reported on these fish species from this water body; however, little work has been reported from other water bodies in the region and other parts of the country (Ahmad et al, 2014;Jaafar et al, 2021), revealing the ambiguity among Schizothorax and Tor genus. But the current study is different from the previous ones (Ahmad et al, 2014) as they focused on the single genus of Schizothorax, but here we Frontiers in Genetics frontiersin.org have adopted an integrative approach to five different genera, including Schizothorax and Tor as well, in a single attempt. Ghouri et al (2020) reported the efficiency of Cyt b for the identification of edible fish species in Pakistan.…”

“…Such a considerable variation between these statements might be due to species ambiguity. Moreover, several findings suggest a vide ambiguity in Schizothorax and Tor genus ( He and Chen, 2006 ; Yang et al, 2012 ; Ahmad et al, 2014 ; Dwivedi et al, 2020 ; Jaafar et al, 2021 ). However, in the region, these species under two genera are mainly considered as Schizothorax richardsonii (Luss) and Tor putitora (Chidak) due to their similarities in morphological traits.…”

“…The Cytochrome b ( Cyt b ) gene, which has ubiquitous uses in taxonomic and ecological domains, is one of the most well-known and targeted DNA markers. It is often used to study the phylogenetic relationships among organisms due to its small size and high nucleotide substitution rate ( Xiao et al, 2001 ; Kumar et al, 2011 ; Ahmad et al, 2014 ; Cornetti et al, 2019 ). In addition, 16S ribosomal RNA has gained popularity due to its extremely high degree of conservation and relatively slow evolution rate ( Hebert et al, 2003 ; Chen et al, 2018 ).…”

DNA barcoding of cyprinids (Labeo rohita, Catla catla and Cirrhinus mrigala), mitochondrial CO1-based study

“…In current investigation, sequences of C. catla follow the neutral evolution (R ¼ .5), while C. mrigala (R ¼ 2.01) and L. rohita (R ¼ 2.84) deviated from it due to external mutations. Such type of deviation was also observed in Schizothoracinae (Ahmad et al 2014;Akhtar and Ali 2016). Examination of CO1 gene of all three species, Catla, Labeo and Mrigala, illustrated very low genetic diversity (<.55) which may be caused by factors such as minimum rate of evolution, decrease in long-term survival, incomplete lineage sorting, inbreeding due to the small size of population, reduced adaptation and fitness (DeSalle and Amato 2004;Frankham 2009).…”