Nutritional Context Influences Preferences of Lambs for Foods with Plant Secondary Metabolites

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Applied Animal Behaviour Science

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An herbivore's nutritional state while foraging may affect its preferences for a chemically defended plant. Increased preference or avoidance of diets with different plant secondary metabolites (PSM) may influence foraging in ways that cannot be predicted solely by the isolated effect of a PSM. Importantly, changes in nutritional context spatially and temporally may affect what herbivores learn, thereby creating variability in herbivores’ foraging behavior. Tannins and terpenes are common defenses in plants, but the extent of protection they provide may be influenced by their biochemical interactions with nutrients in other plants herbivores consume. We determined if the context in which lambs experienced foods with terpenes or tannins influenced their preference for those foods. To do so, we conditioned 20 lambs in two treatments (10 lambs/treatment). Lambs in Treatment 1, first ate tannins mixed with a food of low-nutritional quality for 8 days; they subsequently ate terpenes in the same low-quality food while receiving a basal diet of high-nutritional quality for 8 days. In contrast, lambs in Treatment 2, first ate tannins and then ate terpenes under the same regime described for Treatment 1. When all lambs were offered a choice between the two foods, lambs consumed more of the food—tannin or terpene—they ate while on the high-quality basal diet. Thus, our study supports the hypothesis that the degree to which herbivores avoid plants with secondary metabolites is influenced by the nutritional state of the herbivore while foraging. Our results suggest that individuals experiencing the same PSM under different circumstances may manifest different patterns of preference, which in turn may influence animal productivity and the dynamics of plant communities.

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