The Geographical Differences in the Morphology of <i>Diptychus maculatus:</i> Environmental Driving Factors and Adaptive Evolution

As a typical cold-water fish in the Schizothoracinae subfamily, <i>Diptychus maculatus</i> serves as an important model for understanding species adaptation through morphological differentiation and geographical environment interactions. This study characterized five geographical populations (Kizil River, Toshkan River, Muzati River, Karasu River, and Kyzyl River) in the Tarim River Basin. By integrating traditional morphology (12 traits measured with vernier calipers) and geometric morphometrics (21 landmarks), and using nonparametric tests, principal component analysis (PCA), cluster analysis (CA), and discriminant analysis (DA), we analyzed the environmental driving mechanisms of morphological variation. Results showed 34 morphological traits differed significantly (<i>p</i> < 0.01) among populations. The Kyzyl River population exhibited larger body size and expanded mouth cleft morphology, putatively adaptive to high altitude, low temperature, and food-scarce feeding strategies. The Muzati River population showed greater caudal peduncle height and posterior dorsal fin origin, reflecting locomotor adaptation to rapid-current habitats. The Kizil River population had reduced eye diameter, possibly linked to decreased visual dependence in reservoir slow-flow environments. PCA revealed the first three components explained 87.3% of variance, reflecting body energy, cranial feeding, and sensory function modules. CA divided populations into two clades: Karasu-Toshkan convergence due to moderate-flow habitats, and Kizil River isolation. DA achieved 90.6% accuracy, identifying 19 key traits (e.g., interorbital distance, caudal peduncle height). This study reveals environmental and human-induced (e.g., reservoir blockage) morphological adaptation, providing insights for plateau cold-water fish research.