Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
Research Centre in Evolutionary Anthropology and Palaeoecology, Liverpool John Moores University, Liverpool, UK.
J Morphol. 2022 Sep;283(9):1200-1209. doi: 10.1002/jmor.21496. Epub 2022 Jul 18.
Muroid rodents mostly have a complex stomach: one part is lined with a cornified (nonglandular) epithelium, referred to as a "forestomach", whereas the rest is lined with glandular epithelium. Numerous functions for the forestomach have been proposed. We collated a catalog of anatomical depictions of the stomach of 174 muroid species from which the respective nonglandular and glandular areas could be digitally measured, yielding a "stomach ratio" (nonglandular:glandular area) as a scale-independent variable. Stomach ratios ranged from 0.13 to 20.15, and the coefficient of intraspecific variation if more than one picture was available for a species averaged at 29.7% (±21.5). We tested relationships of the ratio with body mass and various anatomical and ecological variables, including diet. There was a consistent phylogenetic signal, suggesting that closely related species share a similar anatomy. Apart from classifying stomachs into hemiglandular and discoglandular, no anatomical or ecological measure showed a consistent relationship to the stomach ratio. In particular, irrespective of statistical method or the source of dietary information, dietary proxies did not significantly correlate with the stomach ratio, except for a trend towards significance for invertivory (insectivory). Yet, even this relationship was not convincing: whereas highly insectivorous species had high but no low stomach ratios, herbivorous species had both low and high stomach ratios. Thus, the statistical effect is not due to a systematic increase in the relative forestomach size with invertivory. The most plausible hypotheses so far associate the muroid forestomach and its microbiome with a generic protective role against microbial or fungal toxins and diseases, without evident correlates of a peculiar need for this function under specific ecological conditions. Yet, this function remains to be confirmed. While providing a catalog of published depictions and hypotheses, this study highlights that the function of the muroid rodent forestomach remains enigmatic to date.
一部分由角质化（非腺性）上皮组成，称为“前胃”，而其余部分则由腺性上皮组成。人们提出了许多关于前胃的功能。我们整理了 174 种沙鼠类物种的胃解剖描述目录，从中可以对非腺性和腺性区域进行数字测量，从而得出一个“胃比”（非腺性：腺性面积）作为一个与尺度无关的变量。胃比范围从 0.13 到 20.15，对于一个物种，如果有多个图像可用，则种内变异系数的平均值为 29.7%（±21.5）。我们测试了该比例与体重和各种解剖学和生态学变量的关系，包括饮食。结果显示存在一致的系统发育信号，表明亲缘关系密切的物种具有相似的解剖结构。除了将胃分为半腺性和盘状腺性外，没有任何解剖学或生态学指标与胃比显示出一致的关系。特别是，无论统计方法或饮食信息的来源如何，饮食指标与胃比均无显著相关性，只有取食昆虫（食虫性）呈显著趋势。然而，即使这种关系也不令人信服：虽然高度食虫性的物种具有较高的但不是较低的胃比，但草食性物种具有较低和较高的胃比。因此，这种统计学效应不是由于相对前胃大小随食虫性的增加而系统增加所致。迄今为止，最合理的假设是将沙鼠类的前胃及其微生物组与一般性的保护作用联系起来，以防止微生物或真菌毒素和疾病，而在特定生态条件下，这种功能没有明显的特殊需要。然而，这个功能仍然需要被证实。本研究提供了已发表的描述和假设目录，突出了沙鼠类动物前胃的功能至今仍然是个谜。
