Dark or light? Preference of anuran tadpoles to background illumination in response to food and predators

Abstract

Background illumination and its intensity are crucial factors in visual interaction among organisms. In the present study, we used tadpoles of eight sympatric anuran species (Duttaphrynus melanostictus, Microhyla ornata, Uperodon globulosus, Kaloula taprobanica, Euphlyctis cyanophlyctis, Fejervarya orissaensis, Polypedates maculatus, and Polypedates teraiensis) to examine species-specific responses towards background illumination (shade and light), combined with four treatments [without food and predator (F−P−), with food and without predator (F+P−), without food and with predator (F−P+), and with food and with predator (F+P+)], with four coloured backgrounds (green, red, brown, and black) during different hours of a day (early morning, late morning, noon, and afternoon). Anuran tadpoles choose shaded sides over lighter sides, as such microhabitats are used as an effective means of camouflage, but most of the M. ornata tadpoles preferred the opposite. The observations were similar for red, green, and brown backgrounds simulating different natural conditions. The developmental stage and co-occurrence of tadpoles of multiple species do not affect their behavioural responses. These results draw attention to the importance of low illuminated/shaded backgrounds for behavioural responses of anuran tadpoles to environmental changes.