The gut morphology of the African ice rat, Otomys sloggetti robertsi , shows adaptations to cold environments and sex-specific seasonal variation

Abstract

We studied the gut morphology of the ice rat Otomys sloggetti robertsi, a non-hibernating murid rodent endemic to the sub-alpine and alpine regions of the southern African Drakensberg and Maluti mountains. The gut structure of O. s. robertsi is well adapted for a high fibre, herbivorous diet, as is the case with other members of its subfamily Otomyinae. Despite the broad similarity in gross gut morphology with mesic- and arid-occurring otomyines, O. s. robertsi has a larger small intestine, caecum, stomach volume and parts of the colon, which we suggest are adaptations for increased energy uptake and/or poor diet quality in alpine environments. However, O. s. robertsi has a smaller larger intestine than other otomyines, perhaps because it occupies a mesic habitat. Seasonal sexual differences occurred, with females increasing dimensions of the stomach, small intestine length, caecum, and large intestine in summer. Sexual asymmetry in gut morphology may be related to increased energy requirements of females during pregnancy and lactation, indicating phenotypic plasticity in response to poor quality vegetation and a shorter growing season in alpine habitats.

Latitudinal Trends in Digestive Flexibility: Testing the Climatic Variability Hypothesis with Data on the Intestinal Length of Rodents

“…In addition, we also ran the analyses using the middle point of each area (instead of the locality of the institution), but obtained results did not differ from those reported in the text. Sources: 1, Thomomys bottae (Loeb et al 1991); 2, Mus musculus (Kristan and Hammond 2003); 3, Clethrionomys gapperi, Microtus pennsylvanicus, Microtus longicaudus, and Phenacomys intermedius (Norrie and Millar 1990); 4, Peromyscus maniculatus (Green and Millar 1987); 5, Microtus ochrogaster (Gross et al 1985;Hammond and Wunder 1991;Hammond 1993); 6, P. maniculatus (French and Porter 1994); 7, Peromyscus leucopus and P. maniculatus (Derting and Noakes 1995);8, M. ochrogaster and M. pennsylvanicus (Young Owl and Batzli 1998); 9, P. maniculatus (Hammond and Kristan 2000); 10, P. leucopus (Derting and Hornung 2003); 11, Microtus pinetorum (Derting and Austin 1998); 12, Abrothrix andinus (Bozinovic et al 1988(Bozinovic et al , 1990 and Phyllotis darwini (Sabat and Bozinovic 2000); 13, Akodon azarae (del Valle et al 2006); 14, Clethrionomys glareolus and Arvicola terrestris (Lee andHouston 1993, 1995) and Microtus agrestis (McDevitt and Speakman 1994;Lee and Houston 1995); 15, A. terrestris (Woodall 1989); 16, Apodemus agrarius (Brokowska 1995); 17, Otomys sloggetti (Schwaibold and Pillay 2003); 18, Meriones unguiculatus and Microtus brandti (Pei et al 2001a(Pei et al , 2001b. ments as a response to changing environmental conditions.…”

The burrow system of the African ice rat Otomys sloggetti robertsi

“…We found evidence of crude hoarding chambers at the dead end of tunnels but no evidence of long-term caches, so it appears that all cached food taken into the burrow system is consumed during the same day or overnight. A diet of primarily fresh green plant material (Schwaibold and Pillay 2003) precludes long-term storage of plants, but feeding on caches extends the length of feeding time after dark and during inclement weather, which may be an important adaptation in for this non-ruminant herbivore (Schwaibold and Pillay 2003). Similarly, P. brantsii hoards food plants mainly in the afternoon, which are consumed overnight (Jackson 2001).…”

“…This medium-sized rodent (121-143 g) does not hibernate and is apparently poorly adapted physiologically to the alpine habitats (Richter et al 1997). To cope with thermal stress, O. s. robertsi employs behavioural (sun-basking, huddling) and morphological (dense fur, short extremities, modified gut) adaptations (Willan 1990;Schwaibold and Pillay 2003). Moreover, ice rat colonies have numerous burrow holes, and it is likely that the burrow system of ice rats functions as a thermal buffer against climatic extremes, since ice rats retreat into burrows during the coldest and hottest times of the day (Hinze and Pillay 2006).…”

Spatial dichotomy of sociality in the African ice rat

“…Ice rats also displayed mutual avoidance in summer, almost never occurring within 4 m of one another. The alpine environment is characterized by short growing seasons (Schwaibold & Pillay, ) and ice rats possibly defend food patches to obtain sufficient energy to meet reproductive demands (Schwaibold & Pillay, ). Therefore, like other larger mammals (e.g.…”

“…vlei rats Otomys irroratus ). However, they have morphological adaptations, such as an elongated small intestine for increased energy uptake (Schwaibold & Pillay, ) and thick fur for insulation (Rymer, Kinahan & Pillay, ). Behaviourally, they time their activity to the warmest periods (Hinze & Pillay, ) and bask by withdrawing the limbs, tucking in the head and orientating the back to capture the sun's rays (Rymer et al ., ).…”