Carotenoid intake during early life mediates ontogenetic colour shifts and dynamic colour change during adulthood
Description
Carotenoids play an import role as one of the most prevalent pigments in animals. Carotenoid-based colourations account for striking sexually and naturally selected colour adaptations. Several anurans (frogs and toads) change body coloration either slowly and permanently between life stages (ontogenetic colour change), or rapidly and temporarily (dynamic colour change) within minutes or hours. We investigated ontogenetic colour change from orange to green morphs and tested the influence of dietary carotenoids in the Wallace’s flying frog, Rhacophorus nigropalmatus. Conspicuous orange-red colouration in post-metamorphic development and formation of whitish dorsal spots only present in early life stages suggest juveniles imitate bird droppings. At the age of nine months, while all individuals still possessed orange-red body colouration, a 20-week long feeding experiment was performed supplying frogs with either no carotenoid supplementations, or dietary carotenoids once or four times per week. A high carotenoid diet resulted in a faster increase in green colour saturation and high levels of green and yellow chroma of back colouration. Less or no carotenoid supplementation led to an increase in blue chroma, contributing to a dull turquoise appearance often observed in captive bred and raised anurans. Dietary carotenoid availability in early life stages affected adaptive dynamic colour change when exposed to a mild stressor. Our results show that a high carotenoid diet influenced the ability to rapidly and reversibly change body colouration, an adaptation absent in frogs receiving no carotenoids. Dynamic colour changes were likewise performed in response to changing light conditions presumably camouflaging individuals and providing protection from UV irradiation. The ontogenetic and dynamic pigmentation changes are discussed in light of mechanism and function to promote defensive strategies at different life stages and environments to avoid predation. Description of dataset The four datasets contain following colour parameters of each subadult/adult individual for each measurement: total brightness, maximal reflectance, maximal slope, blue chroma, green chroma, UV chroma and maximum average yellow chroma. Dataset "1_OCC" contains the measurements of the first nine months. In the datasets "2_FeedingExperiment" and "3_HandlingStimulus", the different conditions (G1, G2 and G3) indicate the different experimental groups of the feeding experiment (see methods). The dataset "3_HandlingStimulus" contains the measurements of 1) baseline, 2) after handling and 3) resting period of each individual. The dataset "4_LightConditions" contains the measurements of adults and subadults of group G3 of both set ups (set up 1: conditions shade/lit, set up 2: conditions leaf/exposed, see methods).
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Data collection and analysis To determine OCC and DCC we used a spectrometer (JAZ series; Ocean Optics, Dunedin, FL, USA) and the software SpectraSuite (Spectrometer Operating Software; Ocean Optics) to measure the spectral reflectance. The reflectance data were collected for 300–700 nm and expressed in percentage of reflectance relative to a white standard (WS-1 Diffuse Reflectance Standard, Ocean Optics). We analysed brightness, hue and chroma from the reflectance data with Avicol software v6 (Gomez 2006). Brightness corresponds to the total reflectance. Hue was calculated as maximal reflectance searched in the range 300–700 nm and/or the wavelength of the maximal slope. Chroma was calculated as the proportion of the total reflectance.