The American alligator, Alligator mississippiensis, is an opportunistic carnivore that experiences an ontogenetic shift in food and feeding habits with an increase in body size. Alligators frequently feed on invertebrates and small fish as neonates and transition to feeding less frequently on larger vertebrates as they grow. We hypothesized that alligators experience an ontogenetic shift in the regulation of intestinal performance-modest regulation with frequent feeding early in life and wider regulation with less frequent feeding as they increase in body size. We tested this hypothesis by comparing postprandial responses in metabolic rate, organ masses, intestinal histology, digestive hydrolase activities, and intestinal nutrient uptake rates among neonate, juvenile, and subadult alligators. With feeding, alligators of all three age classes experienced a rapid increase in metabolic rate that peaked within 2 d and thereafter declined more slowly to prefeeding rates. Specific dynamic action increased with body mass and was equivalent to 32% of meal energy. For each age class, the majority of organs did not change in wet and dry mass with feeding. For subadult alligators, luminal gut pH varied regionally due to the acidic stomach, which continued to remain acidic with fasting. With feeding, epithelial enterocytes are remodeled from a pseudostratified to a stratified architecture and become infiltrated with lipid droplets. Feeding did not generate any significant change in the thickness of intestinal tissues, though it did induce an increase in enterocyte width and volume for subadults. For each age class, feeding generally did not result in significant changes in pancreatic trypsin, intestinal aminopeptidase, and intestinal nutrient uptake activities and capacities. Mass-specific nutrient uptake rates varied among age classes due to the higher rates exhibited by neonates. Among age classes, intestinal uptake capacities scaled allometrically (mass exponents <1) with body mass. Across these three age classes, the modest regulation of digestive performance with feeding and fasting for alligators appears to be ontogenetically conserved.

中文翻译：

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通过早期个体发育，美国短吻鳄密西西比鳄维持了适度的消化功能调节。

美国短吻鳄密西西比鳄是一种机会性食肉动物，其食物和进食习惯会随着个体发生变化而发生个体发育。短吻鳄经常以无脊椎动物和小鱼为食，而随着它们的成长，它们逐渐过渡为以较大的脊椎动物为食。我们假设鳄鱼在经历肠道发育时会发生自体转变，适度的调节是在生命早期频繁进食，而随着体型的增大，其在较不频繁进食的情况下会进行更广泛的调节。我们通过比较新生儿，未成年和亚成年短吻鳄在代谢率，器官质量，肠道组织学，消化水解酶活性和肠道养分吸收率方面的餐后反应，检验了这一假设。随着喂食 所有三个年龄段的鳄鱼都经历了代谢率的快速增加，并在2 d内达到峰值，此后下降到预饲速度更慢。具体的动态作用随着体重增加而增加，相当于膳食能量的32％。对于每个年龄段，大多数器官的干，湿质量没有随进食而变化。对于亚成年短吻鳄，由于胃呈酸性，肠腔的pH值会局部变化，而空腹则继续保持酸性。通过进食，上皮肠上皮细胞从假复层改造为复层结构，并被脂滴浸润。饲喂虽然确实引起亚成体肠细胞宽度和体积的增加，但并未引起肠组织厚度的任何显着变化。对于每个年龄段，喂养通常不会导致胰蛋白酶，肠内氨肽酶以及肠内营养吸收活动和能力的显着变化。由于新生儿表现出较高的吸收率，因此特定年龄段的体重特定营养素吸收率有所不同。在各个年龄段中，肠道吸收能力与体重呈异比例变化（质量指数<1）。在这三个年龄段中，对鳄鱼的摄食和禁食对消化系统性能的适度调节似乎在遗传上是保守的。1）具有体重。在这三个年龄段中，对鳄鱼的摄食和禁食对消化系统性能的适度调节似乎在遗传上是保守的。1）具有体重。在这三个年龄段中，对鳄鱼的摄食和禁食对消化系统性能的适度调节似乎在遗传上是保守的。