Eat yourself sexy: how selective macronutrient intake influences the expression of a visual signal in common mynas
These datasets and programs were analyzed in the manuscript 'Eat yourself sexy: how selective macronutrient intake influences the expression of a visual signal in common myna'. Producing colored signals often requires consuming dietary carotenoid pigments. Evidence that food deprivation can reduce coloration, however, raises the question of whether other dietary nutrients contribute to signal coloration, and furthermore, whether individuals can voluntarily select food combinations to achieve optimal coloration. We created a two-way factorial design to manipulate macronutrient and carotenoid access in common mynas (<i>Acridotheres tristis</i>) and measured eye patch coloration as a function of the food combinations individuals selected. Mynas had access to either water or carotenoid-supplemented water and could either eat a standard captive diet or choose freely between three nutritionally defined pellets (protein, lipid or carbohydrate). Mynas supplemented with both carotenoids and macronutrient pellets had higher color scores than control birds. Male coloration tended to respond more to nutritional manipulation than females, with color scores improving in macronutrient- and carotenoid-supplemented individuals compared with controls. All mynas consuming carotenoids had higher levels of plasma carotenoids, but only males showed a significant increase by the end of the experiment. Dietary carotenoids and macronutrient intake consumed in combination tended to increase plasma carotenoid concentrations the most. These results demonstrate for the first time that consuming specific combinations of macronutrients along with carotenoids contributes to optimizing a colorful signal, and point to sex-specific nutritional strategies. Our findings improve our knowledge of how diet choices affect signal expression and, by extension, how nutritionally impoverished diets, such as those consumed by birds in cities, might affect sexual selection processes and, ultimately, population dynamics.
Steps to reproduce
MATLAB programs for photo analysis These programs allowed us to accurately select the eye-patch area and extract RGB, hue, chroma and brightness values of the selected area in each photograph. The first program (MeasurePatchesAndScale.m) allows to import and calibrate each photo (by locating the standards) before selecting specific areas of interests on the photograph. Results are saved in a .csv file. The second program (CalibrateRGBandSave.m) uses the previously generated .csv file to calibrate RGB values according to the standard values and calculate hue, brightness and chroma. Results are saved in a new .csv file. MeasurePatchesAndScale.m CalibrateRGBandSave.m Change during fading phase This file contains eye patch coloration paramaters, plasma carotenoid levels and weights collected during the fading phase post-capture. Measurements were taken at capture, after 2, 4 and 8 weeks in captivity. This dataset was used to monitor and plot changes in coloration, plasma levels and weights. Fading_data.csv Change in coloration scores This file contains eye pacth coloration paramaters collected across the experiment period (day 1, 8, 15, 22 and 28). This dataset was used to obtain coloration scores via Principal Component Analysis on hue, chroma and brightness and to test for treatment, sex and interaction effects on coloration scores (PC1) via linear mixed effect models (LMMs). Color_score.csv Change in plasma carotenoid levels This file contains plasma carotenoid levels across the experiment period. This dataset was used to test for treatment, sex and interaction effects on plasma levels via linear mixed effect models (LMMs) and to test for interactive effect of macronutrient intake on plasma levels via generalized additive models (GAMs). Plasma_CAR.csv Diet Selection - Weekly percentage of food consumed This file contains the weekly percentage of food consumed for 40 common myna birds (Acridotheres tristis) during a four-week-long nutritional experiment. Specific macronutrient intake (protein, lipid and carobohydrate) were extracted from the different foods consumed. This dataset was used to test for treatment, sex and interaction effects on macronutrient selection via linear mixed effect models (LMMs). Diet_weekly.csv Diet Selection - Total weekly intake and coloration score This file contains eye pacth coloration scores (Principal Component 1) and total weekly (W1, W2, W3, W4) intake in protein, lipid and carbohydrate of 40 common myna birds (Acridotheres tristis) during a four-week-long nutritional experiment. This dataset was used to determine the interactive effect of macronutrient intake on coloration scores via repeated measure generalised additive models (GAMs). Diet_GAM.csv