A study on the defense mechanisms against acorn tannins in the Japanese wood mouse Apodemus speciosus

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Acorns (seeds of oak trees) are staple resource for forest-dwelling wildlife, but they contain high level of tannins and cause negative effects on consumers, such as injury on gastrointestinal tract and lever and kidney failure. In order to elucidate the defense mechanisms against tannins in the Japanese wood mouse Apodemus speciosus, which heavily rely on acorns during fall and winter, we investigated the role of physiological acclimation against tannins and selective foraging decreasing tannin intake.First, we allocated 26 wood mice into two groups: the acclimated group and the non-acclimated group. Of the 14 mice in the non-acclimated group, 8 died, whereas only 1 of the 12 mice in the acclimated group died. Mean body weight change was -17.9‰ in the non-acclimated group and -2.5% in the acclimated group. Food intake, dry matter digestibility, and nitrogen digestibility were much higher in the acclimated group than in the non-acclimated group. These results indicate that wood mice can mitigate the negative effects of tannins by acclimation. Path analysis revealed that increased secretion of tannin-binding salivary proteins (TBSPs) and abundance of tannase-producing enterobacteria (TPB) may be main elements of the mechanism of acclimation to tannins.Second, we examined the selective foraging against tannins by the wood mouse and revealed that wood mice can selectively consume acorns with low tannin content and avoid ones with high tannin content.These findings indicate that the wood mouse can consume tannin-rich acorns effectively with these physiological and behavioral defense mechanisms against tannins.