Physiological color change in the neotropical Tree Frog (Pithecopus hypochondrialis) as a potential mechanism of nocturnal camouflage

Animals employ various mechanisms for camouflage, including color change, that may facilitate habitat use. However, the extent to which these mechanisms operate under nocturnal conditions is unclear. To investigate this, we combined a background-induced color change experiment with visual modeling to test whether altering backgrounds for a tropical tree frog (Pithecopus hypochondrialis) could induce short-term color change under nocturnal conditions to match the viewing background, as perceived by three predator classes: snakes, mammals, and birds. We demonstrated that frogs can change color multiple times from green to brown and back across grass and leaf litter backgrounds in dim conditions. Frog visual contrast varied by predator and background. Brown frogs matched against leaf litter across all predators, whereas green frogs were more variable and comparatively less well matched against grass. Notably, frogs achieved near-optimal color matching against both backgrounds for avian predators, with green frogs matching into grass and brown frogs matching into leaf litter. Our study provides evidence that P. hypochondrialis undergoes rapid background-induced color changes at night maintaining effective camouflage, at least against avian predators. We emphasize the need to assess rapid color change against visually guided predators in natural conditions and the importance of understanding viewing conditions for illuminating the ecology and evolution of camouflage.