植物槲皮酮对东方田鼠繁殖适合度的影响

Plant-herbivore interaction is one of the central topics in ecology. Herbivores are faced with a food resource of poor quality not only because plants are low in nutrients but also because they produce plant secondary metabolites (PSMs) that have wide-ranging physiological effects from direct toxicity to digestion impairment. However, studies on the influence of dietary tannins on the reproductive fitness of small mammalian herbivores are scarce. The majority of wild mammalian herbivores confront food items which contain a myriad of chemical compounds that are potentially poisonous. The ingestion of plant secondary metabolites including tannins can have a wide range of physiological consequences in mammalian herbivores, from direct toxicity to digestion impairment, lesions of kidney and liver and disturbance of acid-base homeostasis. In contrast, little is known the influence of dietary tannins on the reproductive fitness of small mammalian herbivores. Reed voles(Microtus fortis ) is one of the dominated rodents in the Dongting lake region, The population cycles of voles typically have 5-10 year period. The main food items of voles include Cara spp., ardamine lyruta and Paspalum dischun, Tristurn trfidum, Inpenruta cytindricus, Erigeran annusperus. During the peak phase, reed voles move to dam and hills intake barks of Populus alba, Broussonetia papyrifera. We found that the contents of quebracho in Cara spp, Cardamine hirsute, Imperata cylindrical, Erigeron annuus, Erigeran annusperu were 2.04% , 1.99%, 2.12% and 2.3%, respectively. And the contents of quebracho in Populus alba, Broussonetia papyrifera were up to 8.4% and 11.5%, respectively. Obviously the reed voles ingest queracho in the field as part of their regular diet. To test the hypothesis that the reproductive fitness of reed voles may be improved by ingesting plant that containing low level of plant secondary compounds (PSC) during vole's low population density period, while the reproductive fitness of voles may be inhibited by ingesting the plants that contain high level of PSC during vole's high population density period. The main research contents of this proposal involves : (1) the concentration of condensed tannins-quebracho in main food items grazed by voles from different inhabitats in the field pens; (2) the effects of condensed tannins-quebracho on the reproductive fitness of voles fed freeze-dried powder of poplar bark, the level of freeze-dried powder of poplar bark in the vole's food based on the observation of voles' foraging behavior in field; (3) the response of reproductive fitness of voles fed foods contain different doses of quebracho. On the bases of theses studies, the proposal will enrich and develop the theory of co-evolution between the small mammalian herbivores and plant mediated by plant secondary compounds.

1. 本研究结合野外围栏研究与实验室分析，探讨植物浓缩单宁-槲皮酮对洞庭湖区东方田鼠繁殖适合度的影响。连续4年在不同季节，测定湖滨苔草地、防洪堤坝、湖滨岗地围栏内东方田鼠主要食物项目中浓缩单宁 - 槲皮酮含量的动态变化；以捕鼠笼活捕3种围栏内的东方田鼠，测定其繁殖力和免疫力；模拟东方田鼠在野外围栏内不同种群密度条件下对槲皮酮含量最高的杨树树皮的采食强度，将杨树树皮的冻干粉以及槲皮酮，分别按不同剂量处理东方田鼠，测定植物浓缩单宁-槲皮酮对东方田鼠繁殖力和免疫力的影响。验证在东方田鼠种群密度较低时，摄入较低剂量的PSC可诱导免疫细胞因子的形成，有益于提高动物的免疫功能；而在种群密度高，可利用食物匮乏，迫使动物采食PSC含量高的植物，摄入高剂量的PSC可抑制东方田鼠免疫功能的假设。研究成果可丰富和发展植食性小哺乳动物－植物协同进化的理论体系，对于控制洞庭湖区东方田鼠种群密度具有重要意义。

动物－植物系统的协同进化是现代生态学的重要研究领域之一，植食性哺乳动物采食植物来获取营养和能量，而植物则衍生出各种有毒的植物次生代谢物（Plant Secondary Metabolites，PSMs）来防御植食动物的采食，影响其生长、繁殖或生存。迄今，有关植物次生代谢物对植食性小哺乳动物免疫功能影响的报道极少。东方田鼠（Microtus fortis, Mf）是栖息于洞庭湖区的主要鼠类，种群暴发时严重危害当地农作物的生长。本论文通过连续饲喂东方田鼠以含0、1.5%、3%、5% 和8% 槲皮素的日粮20d，分析东方田鼠体重的变化；其胸腺指数和脾脏指数； T淋巴细胞、B淋巴细胞、巨噬细胞的增殖以及巨噬细胞的吞噬效应；测定CD4+、CD8+及其百分数局；测定血清中各免疫球蛋白和细胞因子水平，以及对东方田鼠繁殖特征的影响。所获结果充分验证了本研究提出的假设。食物中槲皮素浓度较低时，能显著提高东方田鼠的胸腺和脾脏的器官指数，提高淋巴细胞、巨噬细胞的增殖能力，促进巨噬细胞的吞噬能力，维持CD4+ /CD8+的稳定，促进免疫球蛋白和抗炎因子并抑制促炎因子的分泌。而高浓度的植物槲皮素则会限制东方田鼠免疫器官指数，降低免疫细胞的增殖能力、巨噬细胞的吞噬功能以及CD4+ /CD8+的比值，促进抗炎因子并抑制促炎因子和免疫球蛋白的分泌。摄入含不同浓度槲皮素的日粮后，各组之间东方田鼠卵母细胞凋亡有显著性差异。相比于对照组，植物槲皮素浓度在5%以内可显著降低卵母细胞的凋亡；槲皮素浓度升高至8%时，卵母细胞凋亡比例显著升高。说明适宜浓度的植物槲皮素能显著降低东方田鼠卵母细胞的凋亡比列，高浓度的植物槲皮素则会增加东方田鼠的卵母细胞凋亡比例，从而降低了东方田鼠的繁殖适合度。