Induced and constitutive responses of digestive enzymes to plant toxins in an herbivorous mammal

Abstract

SUMMARYMany plants produce plant secondary compounds (PSCs) that bind and inhibit the digestive enzymes of herbivores, thus limiting digestibility for the herbivore. Herbivorous insects employ several physiological responses to overcome the anti-nutritive effects of PSCs. However, studies in vertebrates have not shown such responses, perhaps stemming from the fact that previously studied vertebrates were not herbivorous. The responses of the digestive system to dietary PSCs in populations of Bryantʼs woodrat (Neotoma bryanti) that vary in their ecological and evolutionary experience with the PSCs in creosote bush (Larrea tridentata) were compared. Individuals from naïve and experienced populations were fed diets with and without added creosote resin. Animals fed diets with creosote resin had higher activities of pancreatic amylase, as well as luminal amylase and chymotrypsin, regardless of prior experience with creosote. The experienced population showed constitutively higher activities of intestinal maltase and sucrase. Additionally, the naïve population produced an aminopeptidase-N enzyme that was less inhibited by creosote resin when feeding on the creosote resin diet, whereas the experienced population constitutively expressed this form of aminopeptidase-N. Thus, the digestive system of an herbivorous vertebrate responds significantly to dietary PSCs, which may be important for allowing herbivorous vertebrates to feed on PSC-rich diets. Supplementary material available online at

Individual diet specialisation in sparrows is driven by phenotypic plasticity in traits related to trade‐offs in animal performance

“…different diets require different digestive conditions, enzymes, or detoxification mechanisms for efficient assimilation (Afik & Karasov ; Karasov et al . ; Kohl & Dearing ; Barceló et al . ).…”

“…Consumption of a wide range of resources that differ in quality result in physiological trade-offs associated with resource digestion; e.g. different diets require different digestive conditions, enzymes, or detoxification mechanisms for efficient assimilation (Afik & Karasov 1995;Karasov et al 2011;Kohl & Dearing 2011;Barcel o et al 2016). Thus, nutritional differences in the energy and macromolecular content among diet items may impact digestive performance, which could affect energy budgets when animal are faced with the prospect of switching diets.…”

Low activities of digestive enzymes in the guts of herbivorous grouse (Aves: Tetraoninae)

“…Herbivorous grouse species specialize on a number of plants that are relatively high in fiber and rich in plant secondary metabolites (PSMs), and so might be faced with limited digestibility associated with both fiber and toxins. We have previously shown that some PSMs, such as phenolics and monoterpenes can inhibit digestive enzymes (Kohl and Dearing 2011;Kohl et al 2015). Though, the enzymes of grouse can be more resistant to inhibition by PSMs when compared to domestic chicken (Kohl et al 2015).…”

Animal plant warfare and secondary metabolite evolution

“…changing from few daily meals with high food intake to many meals with low food intake, 19,20 and metabolization and detoxification of toxic PSM taken up with food. [21][22][23][24][25] Another adaptation to PSM that cannot be taken up in unlimited amounts is the evolutionary developments of specialists and generalists. The mixed diet of generalistic herbivores reduce the need for detoxification of similar groups of toxic PSM, whereas herbivores specialist to one or few plant species as food source developed especially improved metabolic detoxification pathways.…”