Divergent skin-response profiles in two high-altitude anurans from the Qinghai-Xizang plateau: Integrated morphological, biochemical, and transcriptomic analysis.

Amphibian skin is a multifunctional physiological interface involved in cutaneous respiration, water balance, immune defense, pigmentation, and environmental sensing. High-altitude anurans from the Qinghai-Xizang Plateau (QXP) provide useful models for examining skin-related trait variation under complex environmental conditions. Here, we compared dorsal skin morphology, antioxidant- and pigmentation-related enzyme activities, and skin transcriptomic profiles between two high-altitude anurans, Rana kukunoris and Nanorana pleskei, sampled from lower- and higher-altitude localities. The two species exhibited distinct, trait-specific skin-response profiles. Histological comparisons based on individual-level values did not reach statistical significance, although the group means showed species-specific directional variation. In R. kukunoris, the higher-altitude group had a greater mean epidermal thickness but lower mean dermal thickness, pigment-cell abundance, and pigment-cell area. In N. pleskei, the higher-altitude group had greater mean numbers of epidermal and dermal pigment cells, granular glands, and mucous glands, but lower mean dermal thickness, granular gland area, and pigment-cell area. The biochemical responses were more pronounced: peroxidase activity was elevated in higher-altitude R. kukunoris, whereas tyrosinase activity was markedly elevated in higher-altitude N. pleskei. Transcriptomic analyses identified species-specific candidate functional signatures related to redox regulation, extracellular matrix organization, immune and inflammatory signaling, DNA repair-related processes, and melanogenesis-associated regulation. Overall, species-associated differentiation was more evident at the biochemical and transcriptomic levels than in the measured histological traits. The descriptive histological patterns, together with the enzyme-activity and transcriptomic profiles, suggest that the two species may differ in the relative contributions of structural, antioxidant, and pigmentation-related processes under multifactorial high-altitude environmental conditions. These findings provide a physiological framework for understanding skin-response variation in plateau amphibians without attributing the observed patterns to a single environmental driver.