The Complex and Well-Developed Morphological and Histological Structures of the Gastrointestinal Tract of the Plateau Zokor Improve Its Digestive Adaptability to High-Fiber Foods

Abstract

The morphological and histological traits of the gastrointestinal tract (GIT) enable the animal to perform some specific functions that enhance the species’ adaptability to environments. The plateau zokor (Eospalax baileyi) is a subterranean rodent that mainly forages on plant roots in the Qinghai-Tibet Plateau, but little is known about the mechanism by which the plateau zokor digests roots that have high fiber contents. In this study, we used comparative anatomy methods to compare the morphological and histological traits of the GIT of both the plateau zokor and the plateau pika (Ochotona curzoniae), a small, fossorial lagomorph that forages aboveground plant parts, in order to clarify the traits of the plateau zokor’s GIT and to understand its adaptations to high-fiber foods. The results showed that the foods which plateau zokors eat have a higher fiber content than those which the plateau pikas eat. The plateau zokor has a double-chambered and hemi-glandular stomach (the tubular glands are only in the gastric corpus II, and the gastric fundus is keratinized), whereas the plateau pika has a simple, wholly glandular stomach. The gross morphological indicators (organ index and relative length) of the GIT were significantly lower in the plateau zokor than they were in the plateau pika (p < 0.001). However, the thickness of the gastric corpus II mucosal layer and the gastric fundus muscle layer are significantly higher in the plateau zokor than they are in the plateau pika (p < 0.001), and the thickness of each layer of intestinal tissue is higher in the plateau zokor than it is in the plateau pika. Additionally, the small intestinal villi also are higher and wider in the plateau zokor than they are in the plateau pika. Our results suggest that instead of adapting to digest the high-fiber diet by expanding the size of the GIT, the plateau zokor has evolved a complex stomach and a well-developed gastrointestinal histological structure, and that these specialized GIT structures are consistent with an optimal energy-economy evolutionary adaptation strategy.

Histomorphological and Histochemical Study of Esophagus and Stomach in the Neonate Guinea Pigs (Cavia porcellus)

“…The thickness of this layer was 23.8±2.3, 21.7±2.7, and 47.3±4.08 subsequently in the three parts. This observation was consistent with the findings published by (Cai et al, 2022), and consisted of some elastic and collagen fibers without any visible submucosal glands. The tunica muscularis in the cranial region of the esophagus consisted of striated muscle fibers, which progressively changed into mixed fibers in the intermediate region and smooth fibers in the caudal region, formed by three layers from outside to inside: The external thinner layer that formed by longitudinal oriented muscle fibers, the middle thicker layer its fibers having a circular disposition, and the internal layer with a longitudinal arrangement of muscle fibers that are present in less than half of the esophageal circumference is not on the entire circumference which agreed with study of (Das and Ranjan, 2016).…”

“…There is a thickened part where there are muscle fibers that surround the base of the esophagus and make up a circular muscle called the esophageal sphincter. These results agreed with (Dyce et al, 2010;Cai et al, 2022) with differences in morphometrical measurements. The histological results showed that the esophagus in all regions (cervical, thoracic, and abdominal) was formed from four tunics: mucosa, submucosa, muscularis, and adventitia or serosa.…”

“…Therefore, the goal of the digestion process is to gradually transform the feed materials into soluble, simple forms that are suitable for consumption and absorption (Al-Aaraji and Addi Ali, 2022). The gastrointestinal tract (GIT), has a very diverse morphological shape and function as a result of adaptation through long-term natural selection processes ( Jiang et al, 2015;Al-Aaraji and Al-Kafagy, 2016;Cai et al, 2022). Rodent GITs have highly specific morphological, histological, and functional traits that have developed over time to accommodate these environmental variations.…”