The comparative gastrointestinal morphology of five species of muroid rodents found in Saudi Arabia.

Meriones rex (King jird), Meriones libycus (Libyan jird), Acomys dimidiatus (Eastern spiny mouse), Acomys cahirinus (Egyptian spiny mouse), and Dipodillus dasyurus (Wagner's dipodil) are five species of small rodents of the superfamily Muroidea with distributions in Eastern Africa, Egypt, and the desert regions of the Arabian Peninsula. Water is scarce in these regions and may result in relatively low-digestible food. The aim of the present study is to describe and compare the gastrointestinal tract morphology and morphometry of these five species in order to elucidate whether morphology is influenced by phylogeny or dietary preference. Each segment of the gastrointestinal tract of each species was macroscopically examined and the length and basal surface area of each segment was measured. Standard histologic procedures were performed to determine a surface enlargement factor to determine the mucosal luminal surface area. A unilocular-hemiglandular stomach was observed in all the species examined. The caeca of all the species were long and arranged into a loose spiral toward the caecal tip with the ileocaecal and caeco-colic openings positioned close together. Two rows of oblique folds could be observed in the proximal colon of all species except in D. dasyurus which had longitudinal folds. Morphometric analysis showed the largest stomach in A. cahirinus and the largest caecum and colon in M. libycus. All the species can be grouped in the family Muridae in two subfamilies and similarities were observed including the hemiglandular stomach and relatively large caecum. It could be concluded that phylogeny plays an important role in determining gastrointestinal morphology while diet plays a subordinate role in the desert rodents in the present study.