Habitat-Driven Sexual Dimorphism in Triplophysa strauchii Between Oxbow Lake and Stream: A Geometric Morphometric...

Sexual dimorphism is widespread among fish species, yet the ecological factors shaping this phenomenon remain poorly understood. Using traditional morphometric analyses of 319 specimens together with geometric morphometrics, this study examined sexual dimorphism in Triplophysa strauchii across two basins. The results showed that both the 42 specimens from the oxbow lake habitat in DL and the 34 specimens from the sedimentary-bottom stream in LS exhibited male-biased sexual size dimorphism (SSD). Males had larger body size, larger heads, and greater caudal peduncle depth, traits that may enhance locomotor and foraging performance. These findings suggest that sexual selection is an important mechanism underlying sexual dimorphism in T. strauchii across different river basins. The operculum also exhibited sexual differences across basins: females had narrower opercula, whereas males had more rounded and obtuse opercula. Canonical variate analysis (CVA) based on Procrustes distances further indicated that sexual dimorphism in opercular shape was more pronounced in DL than in LS. Differences in eye size were also observed: females from Dacao Lake had larger eyes than males, whereas males from Liutiao Stream had larger eyes than females. Together, these results reveal fine-scale variation in fish sexual dimorphism in response to diverse selective forces (these inferences are based on habitat differences and previous studies, not direct field measurements).