Japanese Wood Mouse is known to overcome negative effects of tannins through acclimation mediated by salivary proteins and enterobacteria. This tannin tolerance, a physiological trait, is efficient for feeding on tannin-rich acorns. Our recent study revealed that mice from acorn rich area (Iwate) are more tolerant than mice from acorn free area (Mkiyakejima). Finding genetic basis for this geographic variation may offer evidence for local adaptation, giving better understanding in evolution of mammalian physiological trait. Therefore, we carried out a common garden experiment. All animal used in this experiment is raised under the identical environment, so differences in response to tannin intake is reflected by genetic factors but not environmental factors.

Lab born mice originating from Iwate and Miyakejima were grouped to either tannin-exposed or tannin-free group. They were fed acorns, and then their body weight change was determined as an index of tannin tolerance. As a result, tannin-exposed mice from Miyakejima lost 22% of their initial body weight while mice from Iwate lost only 16%. There was a significant difference in body weight loss among the groups, affected by area and treatment. This result supports the explanation for genetic basis of geographic variation in tannin tolerance.