A flexible digestive strategy accommodates the nutritional demands of reproduction in a free-living folivore, the Koala (Phascolarctos cinereus)
A flexible digestive strategy accommodates the nutritional demands of reproduction in a free-living folivore, the Koala (Phascolarctos cinereus)
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DOI：
10.1111/j.1365-2435.2007.01279.x
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发表时间：
2007-08-01
影响因子：
5.2
通讯作者：
Hume, I. D.
中科院分区：
文献类型：
--
作者：
Krockenberger, A. K.;Hume, I. D.
1. 小型叶食性哺乳动物，如考拉，被认为能量有限，因为它们的肠道容量相对较小，与代谢需求和不易消化的叶片食物的肠道填充作用相比。然而，在哺乳期高峰期，雌性考拉会增加食物摄入量（35%）以满足繁殖所需的营养需求。这项研究探讨了生殖雌性考拉克服食物摄入限制的机制。使用惰性溶质（钴（Co）与EDTA络合）和颗粒标记物（铬(Cr)-与直径600-1180 μ m的细胞壁成分相关）测量了自由生活考拉胃肠道中的食糜潴留。这两种标记物的整个肠道传代速度都比圈养考拉快2-3倍，可能是因为野生考拉的食物摄入量比圈养考拉多35%-69%。与圈养考拉一样，在自由生活的动物中，溶质标记比颗粒标记保留的时间更长，这表明液体、溶质和小颗粒（包括细菌）在后肠盲肠和近端结肠中选择性保留。由于哺乳期动物溶质标记物池大小增加了42%，因此与繁殖相关的食物摄入量增加了35%，而这两种标记物的食糜保留率都没有受到影响。食糜中大颗粒池大小不变。因此，雌性考拉至少在一定程度上通过增加溶质消化池的大小来满足生殖的营养需求，从而最大限度地减少增加食物摄入量对溶质和小颗粒的消化以及粪便中微生物蛋白质的损失的有害影响。有一些迹象表明，它们还可以增加大颗粒的通过速度或提高大小颗粒的分离效率，以减少大的，难以消化的颗粒的肠道填充效应。显然，考拉的消化策略比我们之前认为的更灵活，对食物摄入的限制也不那么严格。雌性考拉适应增加的食物摄入量，以满足自由生活和繁殖的需要，而不影响从桉树叶子中提取营养。我们认为，类似的消化策略的灵活性可能在大多数小型哺乳动物食草动物，特别是树栖叶食性动物满足生殖营养需求的方式中发挥重要作用。
1. Small mammalian folivores, such as the koala, are considered to be energetically limited by their relatively small gut capacity compared with metabolic requirements and the gut-filling effect of their poorly digestible leaf diet. However, during peak lactation, female koalas increase their food intake (35%) to meet the nutritional demands of reproduction.2. This study examines mechanisms by which reproductive female koalas overcome limitations to food intake.3. Digesta retention in the gastrointestinal tract was measured in free-living koalas using inert solute (cobalt (Co) complexed with EDTA) and particle markers (chromium (Cr)-mordanted to cell wall constituents' 600-1180 mu m in diameter).4. The whole gut rate of passage of both markers was 2-3 times faster than in captive koalas, probably because of 35%-69% greater food intakes in the wild. As in captive koalas, the solute marker was retained longer than the particle marker in free-living animals, indicating selective retention of fluid, solutes and small particles (including bacteria) in the hindgut caecum and proximal colon.5. The digesta retention of both markers were unaffected by the 35% increase in food intake associated with reproduction, largely due to a 42% increase in the solute marker pool size in lactating animals. The pool size of large particles in the digesta was unchanged.6. Thus, female koalas meet the nutritional demands of reproduction at least partly by an increased solute digesta pool size, minimizing the detrimental effects of increased food intake on digestion of solutes and small particles, and on faecal loss of microbial protein. There was some indication that they also increase the passage rate of large particles or increase the efficiency of separation of large and small particles to reduce the gut-filling effects of large, poorly digestible particles.7. Clearly the digestive strategy of the koala is more flexible, and limitations to food intake less stringent, than previously thought. Female koalas accommodate the increased food intake required to meet the demands of free-living and reproduction without compromising nutrient extraction from their eucalypt leaf diet. We suggest that similar flexibility in digestive strategy is likely to play an important role in the way that most small mammalian herbivores, especially arboreal folivores, meet the nutritional demands of reproduction.