Gaucher Lucia, Vidal Nicolás, D'Anatro Alejandro, Naya Daniel E
Departamento de Ecología y Evolución, Facultad de Ciencias and Centro, Universitario de la Regional Este, Universidad de la República, Uruguay.
J Morphol. 2012 Jan;273(1):49-56. doi: 10.1002/jmor.11005. Epub 2011 Aug 10.
Digestive flexibility is a widespread phenomenon among animals, and the congruence between empirical data and optimal digestion models strongly supports the idea that it has evolved by natural selection. However, current understanding of the evolution of this amazing flexibility is far from being comprehensive. Evidence from vertebrate tetrapods suggests that there are two major mechanisms for intestinal down-regulation during fasting periods: a decrease in the number of enterocytes in the mucosal epithelium in endothermic species, and a transitional epithelium in concert with a marked hypotrophy of enterocytes in ectothermic species. Here, we analyze the intestinal changes, at the morphological and histological levels, occurring after 9 and 16 days of fasting in a small characid fish species (Hyphessobrycon luetkenii). We found that short-term fasting was correlated with a marked down-regulation of gut size (i.e., caeca and intestine dry mass fall to a 42.3%, while intestinal length was reduced to a 73.9% of the feeding values) and that these changes were accompanied by a shift in intestinal epithelial organization from a simple columnar to pseudostratified one. This result, in conjunction with data on changes in enterocyte turnover rates during fasting in other fish species, suggests that gut regulation at both levels, cell renewal rate and epithelia configuration, is the basal condition to all tetrapods. More data, especially in some key taxonomic groups (e.g., fish that follow an endothermic strategy), will be needed in order to reach a clear understanding of digestive flexibility evolution.
消化灵活性是动物中普遍存在的现象，经验数据与最佳消化模型之间的一致性有力地支持了这一观点，即它是通过自然选择进化而来的。然而，目前对这种惊人灵活性进化的理解还远远不够全面。来自脊椎动物四足动物的证据表明，在禁食期间肠道下调有两种主要机制：恒温动物黏膜上皮中肠细胞数量减少，变温动物中过渡上皮与肠细胞明显萎缩同时出现。在这里，我们分析了一种小型脂鲤科鱼类（Hyphessobrycon luetkenii）禁食9天和16天后在形态学和组织学水平上发生的肠道变化。我们发现短期禁食与肠道大小的显著下调相关（即盲肠和肠道干重降至摄食时的42.3%，而肠道长度降至摄食时的73.9%），并且这些变化伴随着肠道上皮组织从简单柱状向假复层的转变。这一结果，结合其他鱼类禁食期间肠细胞更新率变化的数据，表明在细胞更新率和上皮结构这两个层面的肠道调节是所有四足动物的基本条件。为了清楚地了解消化灵活性的进化，还需要更多的数据，特别是在一些关键分类群（如采用恒温策略的鱼类）中。
