77.4 Friday, Jan. 7 Physiological and evolutionary responses of digestive enzymes to toxin-rich diets KOHL, K.D.*; DEARING, M.D.; Univ. of Utah; Univ. of Utah email@example.com
Diets rich in tannins pose challenges to herbivores through inhibition of digestive enzymes and subsequent reduction in nutrient availability. To counteract these effects, herbivores may increase enzyme expression to maintain optimal activity, or produce enzymes with lower tannin-binding affinity. We tested these hypotheses using two populations of Bryant’s woodrat (Neotoma bryanti): a naïve population with no evolutionary history with creosote bush (Larrea tridentata), a plant rich in tannins, and a population known to feed on creosote (“experienced”). Animals from both populations were fed either a control or 2% creosote resin diet for 5 days. We measured pancreatic amylase and intestinal aminopeptidase-N (APN) activity. Additionally, we conducted in vitro inhibition studies by incubating tissue homogenates with varying levels of extracted creosote resin, and measured relative enzyme activity. Dietary creosote resin significantly increased amylase activity in both populations, but there were no differences in relative inhibition by creosote resin. Animals had similar APN activities across dietary treatment groups. Interestingly, APN inhibition rates varied between populations and diets, with individuals from the population naïve to creoste fed the control diet having higher inhibition rates than all other groups. Thus, the woodrats from the population naïve to creosote produce an enzyme more tolerant of tannins in response to dietary tannins. It is possible that this more tolerant form of the enzyme has been maintained in the naïve population to permit seasonal consumption of tannin-rich plants. In contrast, individuals with evolutionary experience with creosote constitutively express the more tolerant enzyme, presumably to deal with a natural diet that is always rich in tannins.