Disruptive colouration and background matching enable visual camouflage in a tropical rainforest stream frog

Visual camouflage is a crucial survival strategy for animals, helping them to evade predators. In habitats with high environmental heterogeneity, disruptive colouration often offers a stronger adaptive advantage than background matching. However, research on disruptive colouration in amphibians remains limited. This study focuses on the little torrent frog (Amolops torrentis), a diurnal species found in the tropical rainforests of Hainan, China. Using digital photography and image analysis tools, we assessed the effectiveness of its camouflage under natural conditions and examined the relationship between camouflage performance and habitat temperature, humidity and canopy cover. Our results demonstrate that, when viewed through the eyes of four predators — Indian peafowl, wedge-tailed eagles, humans and ferrets — the frog’s colouration exhibits a disruptive camouflage effect. In the ferret and human visual models, the chromatic just noticeable difference (CJND) between the frog and its background substrate was below the predator visual detection threshold. Across all four visual models, the luminance just noticeable difference (LJND) between the frog and its background exceeded the predator visual detection threshold. Further analysis revealed that, in the human visual model, temperature was associated with the degree of chromatic matching, whereas humidity and canopy cover showed no significant correlation with camouflage effectiveness. This study demonstrates that, in tropical rainforest stream environments, A. torrentis likely enhances its survival probability by combining disruptive colouration with chromatic matching strategies, thereby reducing the likelihood of detection by predators.