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

Abstract

Several muroid rodent species are distributed throughout southern Africa. Some species are reportedly classified as opportunistic omnivorous rodents consuming plant, seed, and insect material. This study aims to provide a detailed morphometric analysis of the gastrointestinal tract (GIT) of four such omnivorous species, including stomach content analysis. Fixed GIT specimens (n = 5 of each) of Rhabdomys dilectus (Mesic four‐striped grass mouse), Rhabdomys pumilio (Xeric four‐striped grass mouse), Aethomys chrysophilus (Red rock rat), and Lemniscomys rosalia (Single‐striped grass mouse) were weighed. Length and circumference measurements of each anatomically distinct GIT region were determined to calculate the basal surface area (BSA). Histological sections from each GIT region were used to calculate a surface enlargement factor (SEF). The BSA and SEF were multiplied to calculate the luminal surface area (LSA) of each GIT region. Stomach content was analyzed both macroscopically and histologically. All species had a similar GIT morphology, namely a unilocular, hemiglandular stomach with a clear limiting ridge, which indicated the transition from stratified squamous epithelium to glandular epithelium. A large loosely spiralled cecum was present in all species. A narrowing of the cecal apex accompanied by lymph aggregates, confirmed histologically in both Rhabdomys species, indicated a cecal appendix. A single short colonic loop with a unique folding pattern for each species was present in the proximal colon. The colonic mucosal surface presented with proximal V‐shaped, and distal longitudinal folds. Intermediate transitional S‐shaped folds were present in three species (R. dilectus, R. pumilio, and L. rosalia). Colonic mucosal folds indicated hindgut specialization similar to other muroid rodents. The hindgut specialization was further supported by morphometric analysis, which indicated large BSA and LSA measurements in the cecum and colon. These adaptations are consistent with herbivory, despite stomach content analysis revealing omnivorous tendencies.

Standardised imaging pipeline for phenotyping mouse laterality defects and associated heart malformations, at multiple scales and multiple stages

“…As in humans, the stomach is located on the left under the LLLiL and the spleen runs along it caudally. The colon, as reported previously (Henke et al, 2018; Nguyen et al, 2015), has a short C-shape curvature, going dorsally and on the left. Thus, micro-CT imaging is a simple and powerful technique to resolve the laterality features of visceral organs, both qualitatively (organ position, asymmetric shape) and quantitatively (organ size, number of lobes).…”

“…In the mouse as in the human, the stomach and spleen are localised on the left side of the body. The colon forms a leftward loop in the human, whereas in the mouse, it has a short C-shape curvature, going dorsally and on the left (Henke et al, 2018; Nguyen et al, 2015).…”

“…The mouse provides a good model for the study of laterality defects, given the array of genetics tools available to reproduce genetic alterations, and given anatomical similarities in mammals. However, there are also anatomical variations between the mouse and human, which can be extracted from fragmented analyses of individual mouse organs (Ciszek et al, 2007; Fiebig et al, 2012; Henke et al, 2018; Kaufman and Richardson, 2005; Nguyen et al, 2015; Thiesse et al, 2010; Webb et al, 1996). Thus, a comprehensive description of laterality features in all mouse visceral organs, and its relevance to clinical diagnosis has been lacking.…”

Mammalian intestinal allometry, phylogeny, trophic level and climate

“…The most often-cited work to back this claim is that of Chivers & Hladik [5]; in citing this study, the large overlap in GIT morphology between trophic groups and several other issues (see electronic supplementary material, S1) are often not mentioned, as well as the fact that these analyses were done without accounting for phylogeny. A large number of original studies that investigated digestive tract anatomy came to supportive conclusions, albeit always necessarily on very small datasets [11][12][13][14][15][16], and generally also without accounting for phylogeny. By contrast, large-scale studies that accounted for phylogeny did not confirm an association between diet and intestinal length [17][18][19][20][21] or GIT complexity [22].…”

Unique Running Pattern and Mucosal Morphology Found in the Colon of Cotton Rats

“…Sundevall's jird (Meriones crassus) and the fat sand rat (Psammomys obesus) have a prolonged cecum with curved apex, ileum, and colon located close to each other, forming a unified opening, and the V-shaped colon forming a loop. African muroid rodent species (Rhabdomys dilectus, R. pumilio, Aethomys chrysophilus, and Lemniscomys rosalia) show short, solitary colonic loops in the AC that folded in on itself (Henke et al, 2018).…”