Dataset for: Warmer ambient temperatures reduce protein intake by a mammalian folivore

The interplay between ambient temperature and nutrition in wild herbivores is frequently overlooked, despite the fundamental importance of food. We tested whether different ambient temperatures (10˚C, 18˚C, and 26˚C) influenced the intake of protein by a marsupial herbivore, the common brushtail possum (Trichosurus vulpecula). At each temperature, possums were offered a choice of two foods containing different amounts of protein (57% vs 8%) for one week. Animals mixed a diet with a lower proportion of protein to non-protein (P:NP, 0.20) when held at 26˚C compared to that at both 10˚C and 18˚C (0.22). Since detoxification of plant secondary metabolites imposes a protein cost on animals, we then studied whether addition of the monoterpene 1,8-cineole to the food changed the effect of ambient temperature (10˚C and 26˚C) on food choice. Cineole reduced food intake but also removed the effect of temperature on P:NP ratio and instead animals opted for a diet with higher P:NP (0.19 with cineole vs 0.15 without cineole). These experiments show the proportion of P:NP chosen by animals is influenced by ambient temperature and by plant secondary metabolites. Protein is critical for reproductive success in this species and reduced protein intake caused by high ambient temperatures may limit the viability of some populations in the future.

Methods
These data were collected using twelve adult male common brushtail possums (Trichosurus vulpecula) which were caught in wire cage traps on the Australian National University campus (Canberra, 35.2809° S, 149.1300° E) in November 2016. The possums were housed inside constant temperature rooms (at 10, 18, or 26 °C ± 2°C) with a 12:12 h light cycle and offered artificial diets prepared daily (composition is described in the uploaded dataset). Food was offered at 1630 h and refusals were collected at 0900 h daily. Dry matter intake (DMI) of the two diets was measured by drying a subsample of the food offered at 80 °C and subtracting the dry mass of all food refusals. In addition, we calculated the daily grams of protein (P) and “non-protein” (NP; sum of fats and non-structural carbohydrates) ingested across 7 days for each possum for each temperature. Possums were weighed weekly. 

The first experiment tested whether possums balanced macronutrients differently depending on the ambient temperature. The second tested how the addition of a PSM, cineole influenced the effect of ambient temperature on macronutrient balancing.

Experiment 1: Macronutrient choice at different ambient temperatures
Possums were randomly allocated into three groups of four, and each group was kept at a constant temperature of either 10, 18 or 26 ± 2°C for seven days. The possums were then rotated between the temperature treatments for two more rounds of the experiment, using a randomized crossover design so the number of observations on each treatment was n=12.

Experiment 2: The effects of ambient temperature and cineole on macronutrient choice
Possums were randomly allocated into two groups. One group was kept at 26 ± 2°C for seven nights, while the other was kept at 10 ± 2°C. Possums were offered the two diets differing in macronutrient composition without addition of any 1,8-cinoele for the first six nights. DMI and diet preferences were measured on the fifth and sixth nights and the mean was taken as an estimate of intake of the basal diets. On the seventh night 1,8-cineole was added to both diets at a concentration of 2.45% WM (~7% DM) and DMI and diet preferences were measured again over two nights.