Karasov W H, Petrossian E, Rosenberg L, Diamond J M
J Comp Physiol B. 1986;156(4):599-609. doi: 10.1007/BF00691047.
What digestive adaptations permit herbivorous nonruminant mammals to sustain much higher metabolic rates than herbivorous lizards, despite gross similarity in digestive anatomy and physiology? We approached this question by comparing four herbivorous species eating the same diet of alfalfa pellets: two lizards (chuckwalla and desert iugana) and two mammals (desert woodrat and laboratory mouse). The mammals had longer small and large intestines, greater intestinal surface area, much higher (by an order of magnitude) food intake normalized to metabolic live mass, and much faster food passage times (a few hours instead of a few days). Among both reptiles and mammals, passage times increase with body size and are longer for herbivores than for carnivores. The herbivorous lizards, despite these much slower passage times, had slightly lower apparent digestive efficiencies than the mammals. At least for chuckwallas, this difference from mammals was not due to differences in body temperature regime. Comparisons of chuckwallas and woodrats in their assimilation of various dietary components showed that the woodrat's main advantage lay in greater assimilation of the dietary fiber fraction. Woodrats achieved greater fiber digestion despite shorter residence time, but possibly because of a larger fermentation chamber, coprophagy, and/or different conditions for microbial fermentation. We conclude with a comparative overview of digestive function in herbivorous lizards and mammals, and with a list of four major unsolved questions.
尽管食草性非反刍哺乳动物与食草性蜥蜴在消化解剖学和生理学上总体相似，但是什么消化适应性使前者能够维持比后者高得多的代谢率呢？我们通过比较四种以相同苜蓿颗粒为食的食草动物来探讨这个问题：两种蜥蜴（卷尾蜥和沙漠鬣蜥）和两种哺乳动物（沙漠林鼠和实验室小鼠）。哺乳动物的小肠和大肠更长，肠道表面积更大，按代谢活体重归一化后的食物摄入量高得多（高出一个数量级），食物通过时间也快得多（几小时而不是几天）。在爬行动物和哺乳动物中，食物通过时间都随体型增大而增加，且食草动物的食物通过时间比食肉动物更长。尽管食草性蜥蜴的食物通过时间要慢得多，但它们的表观消化效率略低于哺乳动物。至少对于卷尾蜥来说，与哺乳动物的这种差异并非由于体温调节方式的不同。对卷尾蜥和林鼠在各种饮食成分同化方面的比较表明，林鼠的主要优势在于对膳食纤维部分的同化能力更强。尽管停留时间较短，但林鼠实现了更高的纤维消化率，这可能是因为其发酵腔更大、存在食粪行为和/或微生物发酵条件不同。我们最后对食草性蜥蜴和哺乳动物的消化功能进行了比较综述，并列出了四个主要未解决的问题。
