Hongmei Li

The mountainous regions of Southwest China are biodiversity hotspots where geographical isolation promotes genetic differentiation and species diversification. For cave-dwelling species like the Pterocryptis anomala, how geographical isolation, historical climate, and riverscapes have influenced their evolution remains largely unexplored. Based on 255 samples from the Pearl River and the Yangtze River, this study integrated two mitochondrial genes and two nuclear genes to analyze the genetic diversity and structure of the P. anomala population. Phylogenetic trees based on mitochondrial DNA revealed two distinct clades of P. anomala, while nuclear DNA loci showed no clear separation. Spatial Analysis of Molecular Variance (SAMOVA) confirmed two groups: Clade I (the Yangtze, the Guijiang, and the Duliujiang Rivers) and Clade II (the Nanpanjiang, Hongshui, Dahuanjiang, Youjiang, and Rongjiang Rivers). The divergence time between the two clades was estimated at 13.73 million years ago, which was potentially linked to the impact of the QTP uplift on monsoonal systems. The star-like network analysis and neutrality test results indicated that the population of Clade I has maintained a stable state over a long period, while the population of Clade II showed a trend of expansion. Additionally, geographical features such as the Nanling Mountains and the two major river systems may have obstructed gene flow, leading to genetic differentiation. These findings improved our understanding of this species’ evolutionary history and population structure, offering valuable insights for conservation efforts.

Discogobio is a genus of small, economically important freshwater fishes that are widely distributed in Southwestern China. The species of the genus are morphologically very similar, which makes their taxonomic identification quite challenging. DNA barcoding technology can identify species at the molecular level, thus overcoming the limitations of morphological classification. In this study, we collected 16 morphological species of Discogobio from China, analyzed the mitochondrial cytochrome oxidase I subunit (COI) gene sequences of 206 samples, and applied DNA barcoding to identify the species. The COI amplicon was 651 bp in length, and the mean base contents were: (T) 28.83%, (C) 27.63%, (A) 25.97%, (G) 17.57%. The AT content (54.8%) was higher, and the base composition was biased. The intraspecific differences in the genus Discogobio were not significant, and the genetic distances were all less than 2%. The average interspecific genetic distances (3.94%) were about 18.8 times the average intraspecific genetic distances (0.21%), suggesting that there are barcode gaps among the species of the genus Discogobio. Five different species definition methods, Automatic Barcode Gap Discovery (ABGD), Assemble Species by Automatic Partitioning (ASAP), Bayesian Poisson Tree Process (bPTP), Generalized Mixed Yule Combination (GMYC), and Refined Single Linkage (RESL), were used to infer molecular operational taxonomic units (MOTU). The number of MOTUs ranged from 9 to 18. Phylogenetic analysis based on COI gene haplotypes showed that most species formed well-evolved branches on the phylogenetic tree, and the clustering among species was obvious without mixing. The results of this study provide reliable DNA barcoding information for species identification within the genus Discogobio, which is of great significance for taxonomic identification.

Mitochondrial genomes (mitogenomes) have been widely used in phylogenetic analysis and evolutionary biology. The Labeoninae is the largest subfamily of Cypriniformes and has great economic importance and ecological value. In this study, we sequenced, annotated, and characterized the complete mitogenome of Linichthys laticeps and then constructed the phylogenetic tree with previously published Labeoninae mitogenomes. The mitogenome of L. laticeps was 16,593 bp in length, with an A + T content of 57.1%. The mitogenome contained a standard set of 37 genes and a control region with the same order and orientation of genes as most fish mitogenomes. Each protein-coding gene (PCG) was initiated by an initial ATG codon, excluding COI, that began with a GTG codon. Furthermore, most of the PCGs were terminated by a conventional stop codon (TAA/TAG), while an incomplete termination codon (TA/T) was detected in 7 of the 13 PCGs. Most tRNA genes in L. laticeps were predicted to fold into the typical cloverleaf secondary structures. The K_a/K_s (ω) values for all PCGs were below one. The phylogenetic relationships of 96 Labeoninae mitogenomes indicated that Labeoninae was not a monophyletic group and L. laticeps was closely related to the genera Discogobio and Discocheilus. Overall, our study provided the first complete annotated mitogenome of L. laticeps, which filled a knowledge gap in Labeoninae and extended the understanding of the taxonomy and mitogenomic phylogeny of the subfamily Labeoninae.

By detecting and processing the Magnetic Flux Leakage (MFL) signals to identify and estimate the defects in ferromagnetic materials or structures, for example, in the steel pipelines, the so called Magnetic Flux Leakage Testing (MFLT) technology has been widely used in industry. However, the existing MFLT technology is suitable for locating the defects and rough estimating their sizes based on enormous sample data, incapable to image their Three-Dimensional (3D) shapes and precise estimate their sizes, while the physical model associating the defect geometry details and the MFL signals were still unclear. In this study, (1) the effects of an actual 3D defect are taken into account by introducing a new concept, Depth Field over a surface, i.e., a matrix of loss of material on the testing surface of a structure; (2) the governing equations for the depth field and the MFL signals are derived; (3) an algorithm to reconstruct the 3D defect or the depth field based on the governing equations is developed. This new method does not require huge amount of pulling-test data for calibration purpose as the existing MFLT technology used in industry, and it has been verified via a series of tests with various defects of different shapes in pipelines, the results indicate it is valid for 3D defect reconstruction with high accuracy.