Regulation of toxin intake by herbivorous rodents

Theory predicts that specialist herbivores are capable of consuming large quantities of plant toxins due to enhanced detoxification mechanisms, whereas generalist herbivores are predicted to regulate their dose of plant toxins by adjusting their meal size. Juniper (Juniperus monosperma) contains marked concentrations of toxins, particularly alpha pinene. We investigated the spontaneous feeding behavior of three sympatric herbivorous rodents that consume juniper: a juniper specialist, Neotoma stephensi, and two generalist species, N. albigula and N. devia, on diets with increasing concentrations (0-93%) of fresh juniper. The specialist, N. stephensi, did not regulate toxin intake via meal size at any juniper concentration and consumed significantly higher concentrations of toxin per meal than the generalists at high concentrations of juniper (75%). The generalists, however, did show toxin regulation. The amount of toxin consumed in a single meal did not differ between 50% and 93% for either generalist, however, they regulated intake by two different mechanisms. N. albigula decreased meal size in a dose dependant manner starting at 25% juniper. The decrease in meal size resulted in a regulation of the amount of toxin ingested in a single meal that was consistent across juniper concentrations. In contrast, N. devia, consumed constitutively small meals irrespective of toxin concentration. When given juniper treatments, N. devia foraged later in the night, after terpenes volatilized from the diets, thereby controlling the average amount of toxin ingested per meal. These data provide evidence that N. albigula and N. devia both regulate toxin intake but do so via different mechanisms. Supported by NSF IBN 236402.