Phylogeography of the threatened tetraploid fish, Schizothorax waltoni, in the Yarlung Tsangpo River on the southern Qinghai-Tibet Plateau: implications for conservation

The Himalayan uplift and evolution of aquatic biodiversity across Asia: Snowtrout (Cyprininae: Schizothorax) as a test case

Global biodiversity hotspots are often remote, tectonically active areas undergoing climatic fluctuations, such as the Himalaya Mountains and neighboring Qinghai-Tibetan Plateau (QTP). They provide biogeographic templates upon which endemic biodiversity can be mapped to infer diversification scenarios. Yet, this process can be somewhat opaque for the Himalaya, given substantial data gaps separating eastern and western regions. To help clarify, we evaluated phylogeographic and phylogenetic hypotheses for a widespread fish (Snowtrout: Cyprininae; Schizothorax) by sequencing 1,140 base pair of mtDNA cytochrome-b (cytb) from Central Himalaya samples (Nepal: N = 53; Bhutan: N = 19), augmented with 68 GenBank sequences (N = 60 Schizothorax/N = 8 outgroups). Genealogical relationships (N = 132) were analyzed via maximum likelihood (ML), Bayesian (BA), and haplotype network clustering, with clade divergence estimated via TimeTree. Snowtrout seemingly originated in Central Asia, dispersed across the QTP, then into Bhutan via southward-flowing tributaries of the east-flowing Yarlung-Tsangpo River (YLTR). Headwaters of five large Asian rivers provided dispersal corridors from Central into eastern/southeastern Asia. South of the Himalaya, the YLTR transitions into the Brahmaputra River, facilitating successive westward colonization of Himalayan drainages first in Bhutan, then Nepal, followed by far-western drainages subsequently captured by the (now) westward-flowing Indus River. Two distinct Bhutanese phylogenetic groups were recovered: Bhutan-1 (with three subclades) seemingly represents southward dispersal from the QTP; Bhutan-2 apparently illustrates northward colonization from the Lower Brahmaputra. The close phylogenetic/phylogeographic relationships between the Indus River (Pakistan) and western tributaries of the Upper Ganges (India/Nepal) potentially implicate an historic, now disjunct connection. Greater species-divergences occurred across rather than within-basins, suggesting vicariance as a driver. The Himalaya is a component of the Earth's largest glacial reservoir (i.e., the "third-pole") separate from the Arctic/Antarctic. Its unique aquatic biodiversity must be defined and conserved through broad, trans-national collaborations. Our study provides an initial baseline for this process.

The geography of genetic data: Current status and future perspectives

The biogeography field benefits more and more from the growth and application of genetic data such as nucleotide sequences and whole genomes. It has been perceived by scientists that genetic data may be imbalanced among different geographical regions and taxonomic groups. However, the lack of empirical evidence prevents the understanding of current data volume and distribution of genetic data. Based on the construction of a dataset including records for 365 millions of nucleotide sequences of Animalia, Plantae, and Fungi kingdoms, 6 millions of COI sequences of insects, 77 thousands of COI sequences of mammals, 220 thousands of rbcl sequences of Magnoliopsida, and 44 thousands of ITS sequences of Dothideomycetes, here we present evidence on geographical and taxonomical imbalance of the genetic data, identify major gaps and inappropriate practices in the production, application and sharing of genetic data. We then discuss our perspectives on how to fill up gaps and improve the quantity and quality of genetic data.

Genetic Variation in Schizothorax kozlovi Nikolsky in the Upper Reaches of the Chinese Yangtze River Based on Genotyping for Simplified Genome Sequencing

Simple Summary

Schizothorax kozlovi Nikolsky is a unique cold−water fish in the upper reaches of the Yangtze River in China and has high economic value. In our study, genetic diversity and population structure analyses were performed on seven wild populations in the upper reaches of the Yangtze River by GBS. The above results indicate that the populations of S. kozlovi have different degrees of tolerance and selection pressure in response to temperature and altitude. The Wujiang population was genetically differentiated from the Jinsha River and Yalong River populations. The Wujiang intrapopulation has greater genetic diversity and differentiation than the Jinsha River and Yalong River populations, which demonstrates that the Jinsha and Yalong populations require more attention and resources for their protection. The results of this study will increase our understanding of the diversity of S. kozlovi in the upper reaches of the Yangtze River and provide a basis for the conservation and utilization of wild resources.

Abstract

Schizothorax kozlovi Nikolsky is a unique cold−water fish in the upper reaches of the Yangtze River in China and has high economic value. In our study, genetic diversity and population structure analyses were performed on seven wild populations (originating from the Jinsha River, Yalong River, and Wujiang River) in the upper reaches of the Yangtze River by genotyping by sequencing (GBS). The results indicated that a total of 303,970 single−nucleotide polymorphisms (SNPs) were identified from the seven wild populations. Lower genetic diversity was exhibited among the intrapopulations of the three tributaries, and the Wujiang River population had significant genetic differentiation when compared to the Jinsha River and Yalong River populations. Furthermore, the selected SNPs were enriched in cellular processes, environmental adaptation, signal transduction, and related metabolic processes between the Wujiang population and the other two populations. The above results indicate that the populations of S. kozlovi have different degrees of tolerance and selection pressure in response to temperature and altitude. The Wujiang intrapopulation has greater genetic diversity and differentiation than the Jinsha River and Yalong River populations, which demonstrates that the Jinsha and Yalong populations require more attention and resources for their protection. The results of this study will increase our understanding of the diversity of S. kozlovi in the upper reaches of the Yangtze River and provide a basis for the conservation and utilization of wild resources.

Analysis of Population Genetic Diversity and Genetic Structure of Schizothorax biddulphi Based on 20 Newly Developed SSR Markers

To protect the germplasm resources of Schizothorax biddulphi, we developed and used 20 pairs of polymorphic microsatellite primers to analyze the genetic diversity and structure of populations. A total of 126 samples were collected from the Qarqan River (CEC), Kizil River (KZL), and Aksu River (AKS) in Xinjiang, China. The results showed that 380 alleles were detected in 20 pairs of primers and the average number of alleles was 19.0. The effective allele numbers and Nei’s gene diversity ranged from 1.1499 to 1.1630 and 0.0962 to 0.1136, respectively. The Shannon index range suggested low levels of genetic diversity in all populations. The genetic distance between the CEC and AKS populations was the largest, and the genetic similarity was the smallest. There was a significant genetic differentiation between CEC and the other two populations. The UPGMA clustering tree was constructed based on population genetic distance, and the clustering tree constructed by individuals showed that the AKS population and KZL population were clustered together, and the CEC population was clustered separately. Also, the group structure analysis also got the same result. It can be seen that although the three populations of S. biddulphi do not have high genetic diversity, the differentiation between the populations was high and the gene flow was limited, especially the differentiation between the CEC population and the other two populations. This study not only provided genetic markers for the research of S. biddulphi but the results of this study also suggested the need for enhanced management of S. biddulphi populations.

A Detailed Analysis of the Effect of Different Environmental Factors on Fish Phototactic Behavior: Directional Fish Guiding and Expelling Technique

Simple Summary

Environmental pollution and hydropower development have affected fish survival and caused the extinction of some fish populations and species. To understand the effects of various environmental factors on the behavioral profiles of fish, we established a novel experimental method to measure the sensitivity and phototactic behavior of Schizothorax waltoni to four light colors and two flow velocities at two temperatures under low light intensity. The results showed that S. waltoni preferred the four light colors in the order green, blue, red, and yellow. Schizothorax waltoni showed positive phototaxis in green and blue light but negative phototaxis in red and yellow light. The increased flow velocity intensified the positive and negative phototaxis of fish under different light environments, while an increase in the water temperature aroused the escape behavior. Thus, red or yellow light greater than the phototaxis threshold can be used to move fish away from dangerous areas such as high-turbulent flows or polluted waters, while green or blue light can guide them to safe environments such as fish passage entrance or ideal habitats. Finally, this study provides scientific evidence and application value for restoring fish habitats, fish passages, and fisheries.

Abstract

Optimization of light-based fish passage facilities has attracted extensive attention, but studies under the influence of various environmental factors are scarce. We established a novel experimental method to measure the phototactic behavior of Schizothorax waltoni. The results showed that S. waltoni preferred the four light colors in the order green, blue, red, and yellow. The increased flow velocity intensified the positive and negative phototaxis of fish under different light environments, while an increase in the water temperature aroused the escape behavior. The escape behavior of fish in red and yellow light and the phototaxis behavior in green and blue light intensified as the light intensity exceeded the phototaxis threshold and continued to increase. Thus, red or yellow light greater than the phototaxis threshold can be used to move fish away from high-turbulent flows or polluted waters, while green or blue light can be used to guide them to fish passage entrance or ideal habitats. This study provides scientific evidence and application value for restoring fish habitats, fish passages, and fisheries.

Better Resolution for Cytochrome b than Cytochrome c Oxidase Subunit I to Identify Schizothorax Species (Teleostei: Cyprinidae) from the Tibetan Plateau and Its Adjacent Area

The genus Schizothorax is one of the most diverse groups of schizothoracine fish. Many species within this genus possess highly similar morphological characters and are very difficult to be identified accurately only based on morphology. The present study aims to test the effectiveness of mitochondrial cytochrome c oxidase subunit I (COI) gene and cytochrome b (Cytb) gene for discriminating the Schizothorax fish. A total of 185 individuals of 11 species for COI gene and 264 individuals of 23 species for Cytb gene were used for analyzing, respectively. According to the genetic distances, only one species based on COI gene and five species based on Cytb gene had "barcoding gaps," respectively. The tree-based analysis displayed that four species based on COI gene and six species based on Cytb gene clustered monophyletic group with strong support, respectively. The optimal threshold value of Schizothorax is 0.005 based on COI gene and 0.008 based on Cytb gene. The results of genetic similarity tests performed through online BLAST showed that 108 of 185 similarity searches succeeded in identifying conspecific sequences based on COI gene and 199 of 264 succeeded in identifying conspecific sequences based on Cytb gene. Considering greater interspecific genetic distance in Kimura 2-parameter (K2P) analysis and many clades with higher supporting values in tree-based analysis, we suggest that Cytb gene has better resolution in discrimination of Schizothorax species than COI gene. However, there are still many confused clustering relationships based on molecular data currently available. Incomplete lineage sorting, the existence of possible cryptic species and problematic morphological identification, etc. might have greatly weakened the resolution of Cytb gene in discrimination of Schizothorax species.