高原鼢鼠对毒草的偏好及其解毒途径初探

Because of the huge energy consumption, burrow limitation and seasonal restrictions during burrow foraging activities, the plateau zokors (Eospalax baileyi) should be dietary generalists according to the inference of optimal foraging theory. If so, plateau zokors should also be good at digestion of cellulose. However, studies have showed that, plateau zokors neither be good at digestion of cellulose nor be dietary obligatory generalists, they are in favor of poisonous forbs, which are of low cellulose content but high PSMs (plant secondary metabolites). Based on these evidences we suggest a hypothesis that plateau zokors may be good at detoxification for PSMs in poisonous forbs, this ability made them get access to the energy in poisonous forbs and avoid the .hardship to digest cellulose. For this aim, we designed four experiments. . 1. Cafeteria test. We plan to take fresh toxic plants and non-toxic plants together to conduct cafeteria test on plateau zokors, to confirm that plateau zokors can forage on or even show preference on fresh toxic plants.. 2. Determination of chemical composition. We plan to determinate the chemical composition of the plant appeared in overwinter caches before (in winter) and after hoarding (in spring), and the plant appeared in cafeteria test conducted in summer.. 3. Oral test. We plan to conduct oral test on plateau zokors , using water extract and alcohol extract of the three most famous toxic plants (Stellera chamaejasme, Oxytropis kansuensis and Thermopsis lanceolata), to confirm that plateau zokors can forage and detoxify better than CK rats (Rattus norvegicus).. 4. Liver transcriptome analysis. We plan to conduct transcriptome analysis of the liver from 2 plateau zokors inhabit together with Stellera chamaejasme, 2 plateau zokors inhabit without Stellera chamaejasme, and 2 rats, to confirm that plateau zokors can up regulate the detoxification genes in liver.. Take the four evidences together, we will confirm that, plateau zokors are able to occupy the nutrients of poisonous forbs by their strong detoxification ability, and this will help for our understanding of detoxification physiology and evolution ecology of herbivorous mammals.

挖掘取食能量消耗极大、又受洞道和季节性的限制，据最佳觅食理论，高原鼢鼠的食性应为严格泛化者，且对纤维素的消化率高。但已有研究表明其对纤维素的消化能力不强，我们也发现高原鼢鼠在越冬食物的选择中偏好几种毒草，因此我们提出高原鼢鼠可解PSMs（植物次生代谢物质）之毒的假设。本研究设计以下试验，试证高原鼢鼠的解毒途径应为体内解毒，且对其解毒途径和酶类做初步研究：1、用足量的有毒和无毒鲜草进行自助餐试验，证实高原鼢鼠可取食新鲜毒草；2、分季节测定高原鼢鼠所取食植物的主要PSMs的含量，证实其所偏好的毒草含有较高剂量PSMs；3、用毒草水提物和醇提物对高原鼢鼠进行灌胃试验，检验毒草提取物进入消化道后鼢鼠的生理反应；4、进行高原鼢鼠肝脏转录组分析，证实高原鼢鼠相对于大白鼠，肝脏解毒酶基因表达上调。如此证实，高原鼢鼠已进化出了较强的处理有毒物质的能力，为探讨草食性哺乳类解毒生理和适应进化机制打下基础。

本实验将狼毒等16种植物对高原鼢鼠进行自助餐投喂实验，设置6g/种、9g/种、12g/种三种梯度来观察其采食行为。结果表明：（1）在食物不足时，高原鼢鼠采食部分狼毒，而三组鼢鼠对棘豆均喜食。（2）高原鼢鼠最喜食的植物为平车前、蒲公英、田葛缕等含水量、蛋白质等都丰富的杂类草。（3）最不喜食的植物是垂穗披碱草、狼毒、披针叶黄华、沙棘；高原鼢鼠在取食行为中不选择含有较高纤维素、根系不发达的植物。（4）投喂食物量在一定范围内，随着食物的增多，高原鼢鼠对不喜食的植物取食选择指数降低，对喜食的杂类草取食选择指数增高。.根据味觉测试及比较Ei值，以确定植物味觉是否会影响鼢鼠的饮食选择。结果表明，植物口味在高原鼢鼠的饮食选择中起着重要作用。此外，我们的结果表明，在选择获取营养和避免不利的次生植物代谢物之间存在着明显的权衡。通过测定每一种植物的粗蛋白、粗纤维、水溶性糖和粗灰分的含量，比较分析了营养成分含量在3 种食物类型（喜食、可变和不喜食）间的差异，及其与各种植物选择指数的相关关系。结果表明，高原鼢鼠总体上偏好粗蛋白和水溶性糖含量高、粗纤维含量低的植物，对无机盐的含量则不敏感。.本研究喂食狼毒对高原鼢鼠转录组和肠道微生物的影响。结果显示喂食狼毒后，高原鼢鼠的肝脏转录组差异表达基因不多，随着喂食剂量的增加，上调基因的表达与上升剂量之间没有显著相关关系；二者肠道微生物在喂食狼毒之后，其微生物群落结构也为发生预期的规律性变化。另外，利用高通量测序技术，通过16s rRNA基因我们发现，两种鼢鼠胃肠道不同部位微生物组成均存在部位特异性，且盲肠的微生物多样性高于直肠、小肠和胃，两种鼢鼠直肠对胃微生物贡献率均在84%左右。本研究通过高通量测序技术比较了高原鼢鼠在圈养前和圈养15天后的微生物群落结构和功能，结果表明圈养对高原鼢鼠肠道微生物的影响也不显著。