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

橡子（橡树的种子）是森林野生动物的主要资源，但它们含有高浓度的单宁，对消费者造成负面影响，如胃肠道和杠杆损伤和肾衰竭。为了阐明秋、冬季以橡实为食的日本木鼠斑姬鼠（Apodemus speciosus）对单宁酸的防御机制，我们研究了生理适应和选择性觅食减少单宁酸摄入量的作用。首先，将26只木鼠分为驯化组和非驯化组。在未驯化组的14只小鼠中，有8只死亡，而驯化组的12只小鼠中只有1只死亡。非驯化组平均体重变化为-17.9‰，驯化组平均体重变化为-2.5%。驯化组采食量、干物质消化率和氮消化率显著高于未驯化组。这些结果表明，木鼠可以通过驯化来减轻单宁的负面影响。通径分析显示，单宁结合唾液蛋白（TBSPs）的分泌增加和产单宁酶肠杆菌（TPB）的丰度增加可能是单宁适应机制的主要因素。其次，研究了木鼠对单宁的选择性觅食行为，发现木鼠对单宁含量低的橡子有选择性进食，对单宁含量高的橡子有选择性回避。这些发现表明，木鼠可以通过这些生理和行为防御机制有效地摄取富含单宁的橡果。

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.