Inhibition of β-Glucosidase and Esterase by Tannins from Betula, Salix, and Pinus Species

The reaction of tannin fractions isolated from the bark of Betula, Salix, and Pinus species with two enzymes, -glucosidase and esterase, was investigated. The influence of precipitation to the hydrolytic capacity of -glucosidase also was studied. All tannins studied precipitated -glucosidase and esterase, and moderate differences in the precipitating capacities of the tannins were observed. Interestingly, complex formation between -glucosidase and tannin did not markedly affect the activity of the enzyme. Therefore, complex formation during the insect/herbivore feeding does not necessarily change the defense activity of phenolic glycosides or decrease activity of digestive enzymes.     

Interaction of proteins with sorghum tannin: Mechanism,specificity and significance

The grain of some varieties of sorghum contains 2% or more condensed tannin; many other varieties contain no tannin at all. Agronomic advantages, e.g., resistance to bird depredation, are associated with high-tannin sorghums, which have relatively low nutritional value for nonruminants. The biological effects of tannin are a result of its propensity for binding proteins; both hydrogen bonding and hydrophobic interactions are involved. Sorghum tannins can bind dietary proteins and reduce their digestibility. Purified digestive enzymes are inhibited by tannin, but significant inhibition in vivo is unlikely. Proteins differ greatly in their affinity for tannin. Those with highest affinity are large, have an open structure, contain no bound carbohydrate and are rich in proline. Sorghum proteins of the alcohol-soluble prolamine fraction associate strongly with tannin, are difficult to remove during tannin purification and are found combined with tannin in the indigestible residue after in vitro digestion with pepsin. On germination, the seed may sacrifice a portion of these proteins to bind the tannin that might otherwise interfere with metabolism by inhibiting seed enzymes. During seed development, tannin molecules are relatively short and do not effectively precipitate proteins; as the seed dries, tannins undergo polymerization to an average of ca. 6 flavan-3-ol units/molecule. The antinutritional effects of sorghum tannins can be eliminated by soaking the grain in dilute aqueous alkali, but not by cooking. When rats are put on high-tannin sorghum diets, their parotid glands undergo hypertrophy and produce a group of unique salivary proteins with extremely high affinity for tannin. These proteins contain over 40% proline and are devoid of sulfur-containing and aromatic amino acids. This metabolic adaption may protect rats against tannin by binding and inactivating it immediately when it enters the digestive tract. Presented at the AOCS Meeting, May 11, 1983.     

Preserving leaves for tannin and phenolic glycoside analyses: A comparison of methods using three willow taxa

Members of the Salicaceae often produce phenolic glycosides and condensed tannins. There is much debate on the best method for the preservation of leaf material prior to chemical analysis. Published results indicate freeze-drying, a method commonly used for tannin analysis, may be inappropriate for phenolic glycosides, unless done in a manner to prevent thawing during the drying process. Another commonly employed method, air-drying, is appropriate for phenolic glycosides but inappropriate for condensed tannins. I present evidence using willow leaves that demonstrates that: (1) leaves freeze-dried in external flasks without temperature control contain lower concentrations of phenolic glycosides (salicortin and 2-cinnamoylsalicortin), (2) air-dried leaves have reduced concentrations of condensed tannins, while (3) vacuum-dried fresh leaves have high concentrations of both phenolic glycosides and condensed tannins. Freeze-drying caused salicortin and 2-cinnamoyl salicortin concentrations to drop by 20 mg/g and 4 mg/g, respectively. Salicin, a product of salicortin and 2-cinnamoyl salicortin degradation, is absent in vacuum-dried leaves, present in air-dried leaves and very high in freeze-dried leaves. Thus, the presence of salicin in this system is an artifact of the preservation technique. Condensed tannin concentrations dropped nearly 20 mg/g when leaves were air-dried. Thus, vacuum-drying fresh leaves allows researchers to quantify phenolic glycosides and condensed tannins from the same leaf material.     

Dry bean tannins: A review of nutritional implications

Tannins are one of several antinutritional factors present in dry beans and are located mainly in the seed coat or testa. The tannin content of dry beans ranges from 0.0 to 2.0% depending on the bean species and color of the seed coat. Many high tannin bean varieties are of lower nutritional quality than low tannin varieties of beans. Naturally occurring food legume tannins are reported to interact with proteins (both enzyme and nonenzyme proteins) to form tannin-protein complexes resulting in inactivation of digestive enzymes and protein insolubility. Both in vitro and in vivo studies indicate that bean tannins decrease protein digestibility, either by inactivating digestive enzymes or by reducing the susceptibility of the substrate proteins after forming complexes with tannins and absorbed ionizable iron. Other deleterious effects of tannins include a lowered feed efficiency and growth depression in experimental animals. The antinutritional activity of bean tannins can be reduced by processing (1 or a combination of 2 or more methods), for example dehulling, soaking, cooking and germination. Genetic selection also may help in breeding varieties low in tannins. Potential chemical treatments such as use of tannin complexing agents are discussed. Presented at the AOCS Meeting, Dallas, Texas, April 1984.     

Inhibition of Cyanogenesis by tannins

During isolation of two biosynthetic types of cyanogenic glycosides fromCarica papaya, weak cyanide tests were obtained from initial fractions. Upon final purification, strongly positive cyanide tests were obtained. Pretreatment of extracts to remove polyphenolics alleviated inhibition of cyanogenesis, which led us to suspect that tannins were inhibitory agents. Qualitative and quantitative measures of inhibition were made using standard cyanogenic glycosides and polyphenolics. Cyanogenesis was inhibited quantitatively when condensed tannins (quebracho, wattle, and chestnut), or hydrolyzable tannin (tannic acid) were added. When tannins were precipitated from the reaction mixture, cyanide tests proceeded optimally. These results stress the need to interpret negative cyanide tests with care and indicate possible ecological synergisms between plant defensive chemicals.     

Secondary chemistry of hybrid and parental willows: Phenolic glycosides and condensed tannins inSalix sericea,S. eriocephala,and their hybrids

Salix sericea andS. eriocephala differ markedly in secondary chemistry.S. sericea produces phenolic glycosides, salicortin and 2-cinnamoylsalicortin, and low concentrations of condensed tannin. In contrast,S. eriocephala produces no phenolic glycosides, but high concentrations of condensed tannins. Hybrid chemistry is intermediate for both types of chemicals, suggesting predominantly additive inheritance of these two defensive chemical systems from the parental species. However, there is extensive variation among hybrids. This variation may be due to genetic variation among parental genotypes, which genes were passed on, or to subsequent back-crossing. The differences in chemistry are likely to exert a strong effect on the relative susceptibility of hybrid and parental willows to herbivores.     

Interactions amongHeliothis virescens larvae,cotton condensed tannin and the CryIA(c) δ-endotoxin ofBacillus thuringiensis

The potential interactions among a plant-produced allelochemical, a phytophagous insect, and an endotoxin produced byBacillus thuringiensis were investigated using purified cotton condensed tannins, the CryIA(c)-endotoxin fromB. thuringiensis subsp.kurstaki strain HD-73, and larvae ofHeliothis virescens. Purified condensed tannin from cotton fed to neonateH. virescens reduced feeding and mortality caused by insecticidal crystals ofB. thuringiensis. In fifth instars, tannin reduced relative growth rate (RGR), relative consumption rate (RCR), but antagonized the effects of the crystal-endotoxin. Tannin did not deter feeding of fifth instars in choice tests with cellulose-ester disks. Masking tannin from interacting with the dietary ingredients of artificial diets and crystal protein by encapsulation in alginate gel suggested that tannin adversely affected feeding after ingestion.These results suggest that insect control tactics that employ-endotoxins in microbial insecticides and transgenic cotton plants may not be compatible when used in conjunction with plants containing high tannin concentrations.     

Chemical and Biological Assays to Evaluate Bacterial Inhibition by Tannins

The interactions among purified tannins from three different plants with five strains of ruminal bacteria were investigated. Tannins were purified from crude quebracho (Schinopsis balansae spp.), desmodium (Desmodium ovalifolium), and myrtle (Mirtus communis). The ruminal bacteria studied were Streptococcus bovis JB1, Ruminococcus albus 8, Fibrobacter succinogenes S85, Prevotella ruminicola H₁4, and a recently isolated tannin-tolerant bacterium. Bacterial binding to tannins, rate of tannin binding, and the inhibitory concentrations for each bacterium to each tannin were evaluated. The effects of tannins on glucose utilization and fermentation product formation also were studied. Tannin binding was rapid with little additional binding occurring 10 min after tannin addition. There was variation among bacteria in the amount of tannins bound and in the amount of tannin required to inhibit growth. Condensed tannins from myrtle and desmodium had the highest binding capacity and were most inhibitory to microbes. Absorbance readings from the total phenolics assay were highest for myrtle and lowest for quebracho. Similarly, readings for condensed tannins were highest for desmodium, which also had the largest polymer size. Myrtle and quebracho gave the largest precipitate rings in the radial diffusion assay, a biological assay that measures precipitation of bovine serum albumin by tannins. The relative absorbance values obtained from the total phenolics assay were the most useful predictor of tannin inhibition of microbial growth. The acid–butanol assay and the radial diffusion assay using bovine serum albumin as the precipitable protein were much less useful predictors of tannin biological activity against the bacteria studied.     

Linking chemical reactivity and protein precipitation to structural characteristics of foliar tannins

Tannins influence ecosystem function by affecting decomposition rates, nutrient cycling, and herbivory. To determine the role of tannins in ecological processes, it is important to quantify their abundance and understand how structural properties affect reactivity. In this study, purified tannins from the foliage of nine species growing in the pygmy forest of the northern California coast were examined for chemical reactivity, protein precipitation capacity (PPC), and structural characteristics (¹³C NMR). Reactivity of purified tannins varied among species 1.5-fold for the Folin total phenol assay, and 7-fold and 3-fold, respectively, for the acid butanol and vanillin condensed tannin assays. There was about a 5-fold difference in PPC. Variation in chemical reactivity and PPC can be largely explained by differences in structural characteristics of the tannins determined by ¹³C NMR. In particular, the condensed versus hydrolyzable tannin content, as well as the hydroxylation pattern of the B-ring and stereochemistry at the C-2–C-3 position appear to influence reactivity. Due to the large differences in chemical reactivity among species, it is necessary to use a well-characterized purified tannin from the species of interest to convert assay values to concentrations. Our results suggest that structural characteristics of tannins play an important role in regulating their reactivity in ecological processes.     

The protective effect of antioxidants to a phototoxin-sensitive insect herbivore,Manduca sexta

Photo-activated plant secondary compounds have been shown to be toxic to many organisms including insects. Insect defenses include behavioral mechanisms such as light avoidance, as well as specific biochemical defenses such as antioxidants and antioxidant enzymes. These antioxidant defenses eliminate or quench the deleterious singlet oxygen and free radicals formed by these phototoxins. In this paper we examined the role of dietary antioxidants in protecting the phototoxin-sensitive insect herbivoreManduca sexta. Elevated dietary levels of the lipid-soluble antioxidants-carotene and vitamin E resulted in a concentration-dependent reduction in the mortality associated with treatment ofM. sexta larvae with the phototoxic thiophene-terthienyl. Elevated levels of dietary ascorbic acid had no effect, whereas reduced levels greatly increased the toxicity of-terthienyl. Tissue levels of antioxidants were shown to increase substantially in larvae fed antioxidant-supplemented diets. The results suggest that the ability to absorb and utilize plant-derived antioxidants could be an important defense against photo-activated plant secondary compounds and may have allowed some insects to exploit phototoxic plants.     

Removal of Dissolved Brown Algal Phlorotannins Using Insoluble Polyvinylpolypyrrolidone (PVPP)

Tannins, a large and diverse group of phenolic secondary metabolites, are common in terrestrial plants and marine brown algae. It is sometimes desirable to remove the tannins from plant or algal extracts, e.g., when isolating enzymes and nucleic acids, when using certain colorimetric methods to quantify the tannin content, or to create reliable controls when using tannins in experimental studies. Insoluble polyvinylpolypyrrolidone (PVPP) can be used to specifically remove tannins from solution. In the present study, we evaluated the effect of different factors (amount of PVPP, number of PVPP treatments, type of solvent, pH, and incubation time) on the PVPP removal of dissolved brown algal phlorotannins. Our results imply that there is a limited amount of phlorotannins that can bind to a given amount of PVPP, and that it is preferable to use low quantities of PVPP repeatedly, compared to using fewer treatments with a high amount of PVPP. Furthermore, we found no consistent effect on the removal of phlorotannins due to solvent type (acetone, methanol, distilled water or filtered seawater). There was a slight decrease in the amount of phlorotannins removed from extracts with increasing pH when repeatedly treated with PVPP. All phlorotannins were removed from extracts with pH 6.2, and 89% of the initial phlorotannin content was removed at pH 9.7. These results are compared with previous methodological studies on tannin removal with PVPP. Furthermore, the implications of phlorotannin removal in analytical and ecological investigations are discussed.     

Condensed tannins,attine ants,and the performance of a symbiotic fungus

Field experiments indicate that the foliar concentration of condensed tannin affects the selection of leaf material ofInga oerstediana Benth., a tropical legume tree, by leaf cutter ants. In one study an increase in tannin concentration was correlated with a decrease in the acceptability of leaves to leaf-cutter ants, except at low tannin concentrations. Protein concentration was not correlated with acceptability nor was the ratio of protein to tannin. Results from a second study suggest that when the concentration of tannin was low the ants appear to select leaves on the basis of nutrient availability. Laboratory assays with the ants indicated that quebracho tannin, a commercially available condensed tannin, inhibits foraging ants. Again, at lower concentrations, quebracho tannin appeared to have little affect on the ants. The fungus the ants cultivate is a wood-rotting Basidiomycete that produces enzymes, such as polyphenol oxidase (PPO), that are capable of inactivating tannins. The activity of these PPOs may explain why leaf-cutter ants are undeterred by low concentrations of condensed tannins. I hypothesized that PPO activity would be absent from fungal cultures without tannin and that only high concentrations of tannin would inhibit the fungus. Cultures with and without tannin showed similar PPO activity. Thus PPO activity is constitutive. In fact, as fungal biomass increased, so did PPO activity. As hypothesized, only high concentrations of quebracho tannin inhibited PPO activity and fungal growth. However, it is not clear whether the ants can discriminate between concentrations that do and do not inhibit the fungus.     

Evaluation of Methods for Measuring Polyphenols in Conifer Foliage

There is a resurgence of interest in the quantification of polyphenols in plant tissues because of their presumed ecological importance in plant–litter–soil and plant–animal interactions. The influence of sample preparation, extracting solvent, foliage quality, and assay method was investigated for the quantification of total phenols and condensed tannins in conifer foliage. Our results suggest that it is not possible to recommend a single optimal protocol for quantification of total phenol and condensed tannin fractions from plant materials. In general, the use of aqueous acetone (50–70% v/v) with freeze-dried materials gave the highest recovery. The Folin-Ciocalteau method for total phenols and the butanol–HCl hydrolysis method for condensed tannins appear superior to other common assays tested. There were large differences (1.4–2.2 times) in the reactivity of purified condensed tannins among species, indicating the importance of an appropriate standard for polyphenol quantification. A solid-state ¹³C NMR method with an improved "interrupted decoupling" pulse sequence yielded the highest concentrations for condensed tannins. Assuming that ¹³C NMR provides an accurate measure of total condensed tannin, the other extraction/assay methods used in this study recovered 50–86% of the condensed tannin fraction. The recovery rate is correlated with the nitrogen content of the foliage, which suggests that the formation of protein–tannin complexes may limit the extractability of condensed tannins. While ¹³C NMR condensed tannin values may give the best value for total condensed tannin concentrations, the water-soluble fraction may have the greatest physiological and/or ecological significance.     

Tannin Composition Affects the Oxidative Activities of Tree Leaves

We examined whether tannin composition plays an important role in explaining the oxidative activities of tree leaves of Acer saccharum (sugar maple) and Quercus rubra (red oak). Sugar maple leaves contained substantial amounts of ellagitannins, condensed tannins, and galloyl glucoses, whereas red oak leaves contained almost exclusively condensed tannins. Oxidative activities of the crude phenolics from both species, and the phenolic fractions from sugar maple, were measured with electron paramagnetic resonance (EPR) spectrometry and UV-visible spectrophotometry. The two assays produced similar results: (1) sugar maple phenolics produced larger semiquinone radical concentrations,and higher semiquinone decay rates and browning rates than did red oak phenolics;(2) ellagitannin levels were positively associated with the three measures of oxidative activity; and (3) condensed tannin and galloyl glucose levels were negatively associated with these measures. The negative relationship between condensed tannin levels and oxidative activity resulted from the antioxidant effects of condensed tannins on hydrolyzable tannins; several purified condensed tannins significantly decreased the concentrations of semiquinone radicals and browning rates of pedunculagin (an ellagitannin) and pentagalloyl glucose. As expected, whole-leaf extracts from sugar maple produced elevated levels of semiquinone radicals, but none were observed in red oak extracts when the two species were compared with an EPR time-course assay. We conclude that the oxidative activities of tree leaves may be affected by tannin composition, and that the prooxidant activity of ellagitannins may be decreased by co-occurring condensed tannins.     

Allelopathic Effects of Volatile Monoterpenoids Produced by <Emphasis Type="Italic">Salvia leucophylla</Emphasis>: Inhibition of Cell Proliferation and DNA Synthesis in the Root Apical Meristem of <Emphasis Type="Italic">Brassica campestris</Emphasis> Seedlings

Salvia leucophylla, a shrub observed in coastal south California, produces several volatile monoterpenoids (camphor, 1,8-cineole, -pinene, -pinene, and camphene) that potentially act as allelochemicals. The effects of these were examined using Brassica campestris as the test plant. Camphor, 1,8-cineole, and -pinene inhibited germination of B. campestris seeds at high concentrations, whereas -pinene and camphene did not. Root growth was inhibited by all five monoterpenoids in a dose-dependent manner, but hypocotyl growth was largely unaffected. The monoterpenoids did not alter the sizes of matured cells in either hypocotyls or roots, indicating that cell expansion is relatively insensitive to these compounds. They did not decrease the mitotic index in the shoot apical region, but specifically lowered mitotic index in the root apical meristem. Moreover, morphological and biochemical analyses on the incorporation of 5-bromo-2-deoxyuridine into DNA demonstrated that the monoterpenoids inhibit both cell-nuclear and organelle DNA synthesis in the root apical meristem. These results suggest that the monoterpenoids produced by S. leucophylla could interfere with the growth of other plants in its vicinity through inhibition of cell proliferation in the root apical meristem.     

黑荆树皮单宁不同级分的抑菌性能

通过对黑荆树皮单宁进行醇沉纯化 ,可以使单宁质量分数提高 1 0 %。在此基础上进行萃取分级 ,可得到相对分子质量分布范围不同的单宁级分。各级分的抑菌性能与其浓度和pH有关。根据最低抑菌浓度 (MIC)测试结果 ,黑荆树皮单宁各级分在适宜pH条件下的抑菌性能依次为 :乙酸乙酯级分 >乙醚级分 >纯化后单宁 >水级分 >未纯化单宁。各级分在 1 0g dL质量浓度下对所选霉菌和酵母菌无抑制作用。     

Synthesis and properties of aromatic polyesters and brominated polyesters derived from α,α′-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene

The interfacial polycondensation technique was used for the preparation of polyarylates and brominated polyarylates. Polyarylates and brominated polyarylates were prepared by mixing a solution of diacid chloride such as terephthaloyl chloride, isophthaloyl chloride, or their mixture in dichloromethane with an aqueous alkaline solution of ,-bis(4-hydroxyphenyl)-1,4(or 1,3)-diisopropylbenzene or ,-bis(4-hydroxy-3,5-dibromophenyl)-1,4(or 1,3)-diisopropylbenzene using triethylbenzylammonium chloride as the phase transfer agent. Moderate to high molecular weight polyarylates with _inh up to 1.27 dL/g were obtained, and most of them could be cast into tough and flexible films depending on the polymer composition. In general, polymers containing more 1,3-isomer or isophthaloyl chloride moieties gave transparent and flexible films and had lower glass transition temperatures and higher solubility. Although these polymers have two isopropylidene linkages in their repeating units, they still exhibit moderately high thermal stability and show no obvious weight loss before 400 °C. The introduction of bromine on the polymer backbone caused a decrease of inherent viscosity, crystallinity, and thermal stability of the polyarylates, while causing an increase in glass transition temperature and a great enhancement of fire retardancy.     

Effects of Acacia condensed tannins on urinary parameters,body mass,and diet choice of an Acacia specialist rodent,Thallomys nigricauda

The aim of this study was to investigate the dietary and physiological effects of condensed tannin ingestion on foregut fermenters, using Thallomys nigricauda, a folivorous rodent, as a model. We initially investigated the variability in physiological parameters, such as daily body mass (DM_b), daily feed intake, daily fecal energy loss (FE), daily energy intake (DEI), daily urine pH, and daily urinary ammonia and urea concentrations, in response to different diets with low condensed tannin levels. This experiment was conducted to identify which physiological variables showed the least variation in the absence of tannin. In a second experiment, we investigated the response of the same dietary and physiological parameters to the effects of high dietary condensed tannin ingestion in T. nigricauda. We hypothesized that DM_b, daily feed intake, FE, and DEI of T. nigricauda would be adversely affected by high dietary tannin content. We predicted that detoxification activity by T. nigricauda would increase at higher tannin levels. Ingestion of tannins affected the nutritional status of T. nigricauda, as shown by a decrease in body mass at high tannin levels. We also found that fewer ammonium ions were excreted in the urine by T. nigricauda, as would be expected if this were a means of regulating metabolic acidosis. The urine produced was more alkaline. This result indicates that T. nigricauda is not metabolizing these allelochemicals. Urea production was initially reduced, indicating conservation of bicarbonate ions that will neutralize blood acidity if there is detoxification. A diet choice experiment showed that tree rats avoid high tannin diets, even to the extent that they lose body mass on an alternative diet. This last-mentioned result is noteworthy because previous studies of the effects of tannins on herbivorous mammals have shown that there is physiological control rather than behavioral avoidance of the negative effects of tannin ingestion.     

Effects of Four Monoterpenes on Germination, Primary Root Growth, and Mitochondrial Respiration of Maize

The effects of four monoterpenes—camphor, eucaliptol, limonene, and -pinene—on the oxidative metabolism of mitochondria isolated from maize root (Zea mays), on maize seed germination, and on primary root growth were investigated. The effects of individual monoterpenes on respiration were variable. -Pinene concentrations of 0.05–1.0 mM stimulated respiration with a mixture of substrates composed of NADH, L-malate, succinate, and L-glutamate, and in the absence of exogenously added ADP (basal respiration). However, at concentrations higher than 1.0 mM, -pinene inhibited respiration both in the absence (basal respiration) and presence of ADP (coupled respiration). Limonene at 0.1 mM or above stimulated basal respiration and inhibited in parallel the coupled respiration. Similar effects were promoted by eucaliptol, but at a higher concentration range (1.0 mM or above). Camphor was less active. At 10 mM concentration, it caused stimulation of basal respiration but did not affect coupled respiration. In the concentration range 0.1–10.0 mM, limonene was inactive on seed germination and primary root growth. Camphor and eucaliptol did not inhibit germination but reduced fresh and/or dry weight of roots at 5.0 mM and above. -Pinene inhibited both seed germination and fresh weight of primary roots at 10.0 mM concentration. The results indicate that intact seeds and primary roots are less sensitive than isolated mitochondria. The relatively more lipophilic monoterpenes -pinene and limonene had less activity than the more water-soluble oxygenated monoterpenes camphor and eucaliptol in inhibiting seed germination and/or primary root growth, despite the fact that they had a higher activity on the oxidative metabolism of isolated mitochondria. The findings suggest that the solubility of monoterpenes may be the major factor implicated in these differences.     

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

Mammalian herbivores adopt various countermeasures against dietary tannins, which are among the most widespread plant secondary metabolites. The large Japanese wood mouse Apodemus speciosus produces proline-rich salivary tannin-binding proteins in response to tannins. Proline-rich proteins (PRPs) react with tannins to form stable complexes that are excreted in the feces. Here, we developed a new method for estimating the tannin intake of free-living small rodents, by measuring fecal proline content, and applied the method to a field investigation. A feeding experiment with artificial diets containing various levels of tannic acid revealed that fecal proline content was clearly related to dietary tannin content in three species (A. speciosus, Apodemus argenteus, and Myodes rufocanus). We then used fecal proline content to estimate the tannin intakes of these three forest-dwelling species in a forest in Hokkaido. In the autumn, estimated tannin intakes increased significantly in the Apodemus species, but not in M. rufocanus. We speculated that an increase in tannin intake during autumn may result from consumption of tannin-rich acorns. This hypothesis was consistent with population fluctuation patterns of the three species, which were well-synchronized with acorn abundance for the Apodemus species but not for M. rufocanus.