The colonic groove or furrow: A comparative morphological study of six species of African mole‐rats (Rodentia, Bathyergidae)

Abstract

Herbivorous mammals such as nutrias, guinea pigs, chinchillas, and mole-rats have a longitudinal mucosal colonic groove (furrow) in their ascending colon, which is thought to play a role in the colonic separation mechanism (CSM). It is not known whether this groove is structurally modified to adapt to this function in mole-rat species. The morphology of this groove was studied in 32 mol-rats, four species, one of which consisted of three subspecies, endemic to southern Africa and two species found in eastern Africa. The macroscopic morphology of the groove was documented, and samples for histological examination were taken. The groove was wide at its origin at the cecocolic junction and was lined on either side by a row of papillae with the opposing papillae slightly offset in arrangement. The papillated groove gradually decreased in size toward the distal part of the ascending colon where it disappeared. This pattern was similar in all species except in Heterocephalus glaber, where the papillae were absent and the groove was lined by two longitudinal ridges. A histological examination of cross sections revealed that the mucosa covering the inner and outer walls of the groove was rich in mucous-secreting goblet cells. The walls of the groove contained smooth muscle extending from the inner circular smooth muscle layer at the base to the tips of the papillae in all species examined as well as arteries, lymphatic vessels, and prominent sinusoid-like veins. The groove could be demonstrated both macroscopically and histologically in three Bathyergus suillus fetuses of varying sizes. The sinusoid-like veins present in all grooves, regardless of macroscopic shape, suggest that they have a role in the functioning of the groove.

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

“…Having a CSM has been associated with coprophagy (Björnhag & Snipes, ), which has been reported in H. emini , but not T. splendens . The colonic groove in T. splendens was narrow and nonpapillated and was similar to the delicately papillated groove described in another East African mole‐rat species, namely H. glaber (naked mole‐rat; (Kotzé, Van der Merwe, Ndou, O'Riain, & Bennett, ). The histological structure of the colonic groove was similar to H. glaber where the mucosa of the colonic groove and its ridges were similar to that of the rest of the colon.…”

“…glaber where the mucosa of the colonic groove and its ridges were sim-ilar to that of the rest of the colon. The colonic groove of H. emini resembled that of Georychus capensis (Cape mole-rat) in that the groove walls were low ridges and was wide in the proximal colon and narrowed as it progressed to the distal colon (Kotz e et al, 2009). However, the papillae were not as robust as described in the other Bathyergidae, but was more delicate and similar to that observed in H. glaber Similar V-shaped mucosal folds to those observed in T. splendens have been observed in insectivorous rodents Acomys spinosissimus (Southern African spiny mouse) (Boonzaier et al, 2013) and Jaculus jaculus (Lesser Egyptian jerboa) (Pereira et al, 2016), but not reported in other African mole-rat species (Kotz e et al, 2010).…”

“…The histological structure of the colonic groove was similar to H. glaber where the mucosa of the colonic groove and its ridges were similar to that of the rest of the colon. The colonic groove of H. emini resembled that of Georychus capensis (Cape mole‐rat) in that the groove walls were low ridges and was wide in the proximal colon and narrowed as it progressed to the distal colon (Kotzé et al, ). However, the papillae were not as robust as described in the other Bathyergidae, but was more delicate and similar to that observed in H. glaber (naked mole‐rat) (Kotzé et al, ).…”

“…The colonic groove of H. emini resembled that of Georychus capensis (Cape mole‐rat) in that the groove walls were low ridges and was wide in the proximal colon and narrowed as it progressed to the distal colon (Kotzé et al, ). However, the papillae were not as robust as described in the other Bathyergidae, but was more delicate and similar to that observed in H. glaber (naked mole‐rat) (Kotzé et al, ). Histologically, the colonic groove was similar to that described in Georychus capensis where there was no difference in the mucosa covering the luminal and furrow sides of the papilla and the submucosa of the groove wall contained smooth muscle extending from the inner circular smooth muscle layer into the tip of the papillae (Kotzé et al, ).…”

“…These colonic grooves may be examples of a mucus dependent colonic separation mechanism (CSM) or rodent CSM, which are adaptations for hindgut fermentation (Bj€ ornhag & Snipes, 1999;Sperber et al, 1983). This type of CSM traps microbes in the mucus, which are moved back into the cecum through retroperistalsis along with the digesta, allowing for further fermentation to take place (Sakaguchi, 2003 & Bennett, 2009). The histological structure of the colonic groove was similar to H.…”