Comparative gastrointestinal morphology of Tachyoryctes splendens (Rüppell, 1835) and Heliophobius emini, (Noack, 1894) two species of East African mole‐rats

Abstract

Tachyoryctes splendens (Northeast African mole-rat) and Heliophobius emini (Emin's mole-rat) are two African mole-rats that represent separate allopatric rodent families namely Spalacidae and Bathyergidae respectively. While these species consume a similar diet of underground plant storage organs such as roots and tubers, T. splendens has been reported to additionally consume small amounts of aerial foliage. This study aims to provide detailed gross morphological and histological morphometric analyses of the gastrointestinal tract (GIT) of these two subterranean species. The formalin fixed gastrointestinal tracts of T. splendens (n = 9) and H. emini (n = 6) were photographed, weighed and measured. The length and basal surface areas were calculated for each anatomically distinct region. Representative histological samples were prepared and stained using Hematoxylin and Eosin. Microscopic luminal measurements were used to calculate a surface enlargement factor and the luminal surface area of each region. Tachyoryctes splendens had a large double chambered hemi-glandular stomach with a macroscopically visible transition from keratinized stratified squamous epithelium to glandular epithelium. The cecum was large and the luminal surface revealed a single spiral fold. The ascending colon of T. splendens was arranged in a spiral, with two centripetal and two centrifugal windings. The descending colon was arranged in a single parallel loop, similar to H. emini. A narrow colonic groove was accompanied by V-shaped folds on either side. Heliophobius emini had a simple glandular stomach, a large, haustrated cecum that displayed a cecal appendix and the descending colon was arranged in a single parallel loop. The internal aspect of the colon revealed a wide colonic groove extending from the ceco-colic junction to distal colon. As both species originate from a similar geographical region and ingest very similar diets, it is likely that the differences in the GIT morphology are attributed to phylogeny as the species represent two different families of mole-rats.

Morphometric analysis of the gastrointestinal tract of four African muroid rodent species (Rhabdomys dilectus, Rhabdomys pumilio, Aethomys chrysophilus, and Lemniscomys rosalia)

“…Aethomys chrysophillu s was the most distantly related to the other three species yet displayed few statistically significant morphometric differences. Therefore, the significant differences in morphometric analysis between the four species are unlikely to be caused by phylogeny as suggested in previous research on more distantly related species (Pereira et al, ; Sahd et al, ). Clearly, herbivorous rodent traits, namely a hemiglandular stomach and hindgut specialization, were similarly present in all four species, while typical insectivorous GIT traits such as a simple glandular stomach and the absence of a cecum or hindgut specialization were not represented.…”

“…Lymphoid tissue was found in the cecal apex of all species studied here; however, the additional narrowing of the cecal apex seen in the Rhabdomys species indicated the presence of a cecal appendix similar to that described in a wide range of mammalian species (Smith et al, ; Smith, Parker, Kotzé, & Laurin, ). A cecal appendix was previously reported in other muroid rodents, namely, voles and lemmings (Smith et al, ) as well as in certain hystricomorphic rodents, such as in Bathyergus suillus (Cape dune mole‐rat; Kotzé, Van Der Merwe, & O' Riain, ) Georychus capensis (Cape mole‐rat; Kotzé et al, ), and Heliophobius emini (Emin's mole‐rat; Sahd, Pereira, Bennett, & Kotzé, ). The lymphoid tissue seen in the present study further supports the underlying immune function of the appendix, and the narrowing may be linked to its putative role in acting as a “safe house” or reservoir for commensal bacteria in cases of loss of the normal microbiome (Bollinger, Barbas, Bush, Lin, & Parker, ).…”

“…Similar folds have been described in other muroid rodents, such as A. dimidiatus (Eastern spiny mouse), Acomys cahirinus (Egyptian spiny mouse; Walters et al, ) , A. spinosissimus (Southern African spiny mouse; Boonzaier et al, ), Meriones rex (King jird), Meriones libycus (Libyan jird; Walters et al, ), and Jaculus jaculus (Lesser Egyptian jerboa; Pereira et al, ). Interestingly, in the muroid rodent, Tachyoryctes splendens (East African mole‐rat) V‐shaped folds are accompanied by a longitudinal colonic groove, normally associated with hystricomorph rodents (Kotzé, Van der Merwe, Ndou, O'Riain, & Bennett, ; Sahd et al, ). The colonic groove is typically found in amongst others, African mole‐rats and is indicative of a colonic separation mechanism (CSM) where large and small particles and microbes are separated to be returned to the cecum for longer retention (Björnhag, ).…”

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

“…Our results have showed that the mucosal layer of the gastric corpus II was significantly thicker in the plateau zokor than it was in the plateau pika, and the muscular layer in other parts of the stomach was also significantly thicker in the plateau zokor than in the plateau pika. These results indicate that the unique stomach histology of the plateau zokor can not only ensure that the gastric glands secrete enough gastric acid, mucus and other substances for chemical digestion, but—as a result of the thicker muscular layer in the gastric fundus—also strengthen the contraction and peristalsis of the stomach [ 47 ], which has a strong mechanical digestion function. Furthermore, our analysis of the gastric ultrastructure of the plateau zokor confirmed that the functional cells in the gastric tissue were highly differentiated and highly matched with their high-fiber food, indicating that they have a strong digestive ability.…”

Morphology of the digestive system of the lesser bamboo rat (Cannomys badius)

“…Even though many studies have examined the GIT morphology of rodents in relation to their feeding behaviour and diet, the data for Spalacidae are limited, being available only in two spalacid species: Spalax leucodon (lesser blind mole‐rat; Gorgas, 1967; Tammam et al, 2017) and Tachyoryctes splendens (northeast African mole‐rat; Sahd et al, 2017), and is lacking for C. badius . Biological studies of this species are hardly accessible due to the need for proficiency in habitat analysis and animal tracking.…”