Differential regulation of plant secondary compounds by herbivorous rodents

1. Theory predicts that herbivores will regulate doses of potentially toxic plant secondary compounds (PSCs) by adjusting meal size, the interval between meals and water intake. Furthermore, the PSC concentrations at which these behavioural modifications are employed are predicted to be species dependent because of interspecific variation in biotransformation capacities. 2. To investigate these hypotheses, we examined ingestive behaviour of two species of rodents that differ in diet breadth and biotransformation capacity. We compared the spontaneous feeding behaviour of Neotoma stephensi, a juniper specialist, and Neotoma albigula, a generalist, fed a series of diets with increasing concentrations of one-seeded juniper (Juniperus monosperma). Juniper contains significant quantities of PSCs, particularly alpha-pinene, a diuretic. We fed each species a series of diets with increasing concentrations of juniper. 3. The specialist, N. stephensi, did not regulate PSC intake at any juniper concentration nor did it alter its drinking behaviour. The generalist, however, showed PSC regulation by decreasing meal size in a dose-dependent manner, by increasing the interval between meals, and by substantially increasing water intake. 4. Water consumption was the only factor that could significantly predict an individual’s ability to maintain body mass, which suggests that water consumption may be exceptionally important as the PSC content of an individual’s diet varies. 5. These data provide support for the hypotheses that generalist herbivores can and do behaviourally regulate PSC intake and suggest that the differences in foraging behaviour may be correlated with diet content and biotransformation capacity.