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% 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°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 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'.

A hot lunch for herbivores: physiological effects of elevated temperatures on mammalian feeding ecology.

Mammals maintain specific body temperatures (Tb ) across a broad range of ambient temperatures. The energy required for thermoregulation ultimately comes from the diet, and so what animals eat is inextricably linked to thermoregulation. Endothermic herbivores must balance energy requirements and expenditure with complicated thermoregulatory challenges from changing thermal, nutritional and toxicological environments. In this review we provide evidence that plant-based diets can influence thermoregulation beyond the control of herbivores, and that this can render them susceptible to heat stress. Notably, herbivorous diets often require specialised digestive systems, are imbalanced, and contain plant secondary metabolites (PSMs). PSMs in particular are able to interfere with the physiological processes responsible for thermoregulation, for example by uncoupling mitochondrial oxidative phosphorylation, binding to thermoreceptors, or because the pathways required to detoxify PSMs are thermogenic. It is likely, therefore, that increased ambient temperatures due to climate change may have greater and more-specific impacts on herbivores than on other mammals, and that managing internal and external heat loads under these conditions could drive changes in feeding ecology.