Does acclimation reduce the negative effects of acorn tannins in the wood mouse Apodemus speciosus?

Acclimation as a mechanism of mitigating the damaging effects of acorn tannins was examined in the Japanese wood mouse Apodemus speciosus Temminck, 1844. Mice were fed the two types of diet: a control diet (laboratory chow for mice), and acorns of Quercus serrata (QS), which differ in tannin contents (control = 0%, QS = 2.7% tannic acid equivalent). Body weight changes and digestive abilities were compared between the first stage (Days 1 to 5; Day 0 was defined as the first day of acorn feeding) and the second stage (Days 6 to 10). The amount of salivary proline-rich proteins (PRPs), which are thought to be defensive products to tannins, was measured before and after the experiment. The responses of the wood mice to QS acorns differed between stages: decreases in body weight during the second stage were less than half those that occurred during the first stage; digestive abilities tended to improve; and the relative amount of PRPs after the experiment increased by a factor of five compared with the value recorded before the experiment in the QS-feeding mice. These results suggest that the negative effects of ingesting acorn tannins may be reduced by acclimation, which may result primarily from the induction of PRP production.