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 degrees C, 18 degrees C and 26 degrees 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% versus 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 degrees C compared to that at both 10 degrees C and 18 degrees 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 degrees C and 26 degrees 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 versus 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.This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.