Effects of Tannins on Digestion and Detoxification Activity in Gray Squirrels (Sciurus carolinensis)

Abstract

Acorn tannins may affect food preferences and foraging strategies of squirrels through effects on acorn palatability and digestibility and squirrel physiology. Captive eastern gray squirrels (Sciurus carolinensis) were fed 100% red oak (Quercus rubra) or white oak (Quercus alba) acorn diets to determine effects on intake, digestion, and detoxification activity. Red oak acorns had higher phenol and tannin levels, which may explain the lower dry matter intakes and apparent protein digestibilities and the higher glucuronidation activities observed in squirrels. Although the white oak acorn diet had lower apparent protein digestibilities than the reference diet, it did not suppress dry matter intake for a prolonged period or stimulate glucuronidation. Negative physiological effects of a 100% red oak acorn diet suggest gray squirrels may require other foods to dilute tannin intake and provide additional nutrients. To distinguish the roles of different tannin types in the observed effects of acorn diets on squirrels, squirrels were fed rat chow containing no tannins, 4% or 8% tannic acid (hydrolyzable tannin), or 3% or 6% quebracho (condensed tannin). Apparent protein digestibilities were reduced by tannic acid and quebracho diets. Only the 8% tannic acid diet tended to increase glucuronidation. Specific effects of tannins may largely depend on tannin type, composition, and source and on other nutritional and physiological factors.

The energetics of autumn mast hoarding in eastern chipmunks

“…Average dry mass of shelled acorns was assumed to be 1.57 g, based on measurements made on a subsample (n=30) of acorns collected during the study period for another project (Humphries et al 2001), and was multiplied by red oak acorn energy content (22.13 kJ/g dry mass; Chung-MacCoubrey et al 1997) and digestibility (80%; Humphries et al 2001). In the rare instances when food other than acorns was delivered to the burrow, loads likely consisted of mushrooms, bulbs, and other miscellaneous items (Elliot 1978; C.L.…”

How plants manipulate the scatter-hoarding behaviour of seed-dispersing animals

“…ChungMacCoubrey et al (1997) found a negative correlation between tannin content and protein digestibility in acorns. At high concentrations, tannins can also damage gut epithelium and liver and kidney tissues (Fleck & Layne 1990;Chung-MacCoubrey et al 1997). Finally, tannins at high levels can incur metabolic costs because of increased detoxification requirements (Chung-MacCoubrey et al 1997).…”

“…locomotion, cognition) that could increase the risk of predation, but these possible effects have not been studied. Many granivorous animals cannot be sustained on a diet of acorns that contain high levels of tannins (Koenig & Heck 1988;Briggs & Smith 1989;Koenig 1991;Chung-MacCoubrey et al 1997). The presence of secondary chemicals can act to reduce the immediate value of food, decreasing the likelihood that a seed-caching animal will eat it, but as the food still has potential value during some future period of food scarcity, the animal is likely to store it.…”

Interspecific Differences in Tannin Intakes of Forest-Dwelling Rodents in the Wild Revealed by a new Method Using Fecal Proline Content

“…Tannins are a widespread group of PSMs that are broadly distributed in various plant parts (Waterman and Mole 1994). Ingesting tannins, a diverse group of watersoluble phenolics with high affinity for proteins, may have negative effects on herbivores, such as reduction in protein digestibility (Robbins et al 1987;Chung-MacCoubrey et al 1997;Shimada and Saitoh 2003), damage to the gastrointestinal mucosa and epithelium (Meiser et al 2000), or endogenous nitrogen loss (Shimada and Saitoh 2003).…”