Seasonal changes in body composition of Ctenomys talarum (Rodentia: Octodontidae): An herbivore subterranean rodent

Diet effect on osmoregulation in the subterranean rodent Ctenomys talarum

Water conservation requires osmoregulatory skills, sometimes limited by the environment and/or physiological and behavioral characteristics acquired along the evolutionary history of the species. Fossoriality had probably emerged as a survival mechanism to face increasing aridity, as suggested for Ctenomys, a genus that radiated to different environments. Ctenomys talarum (tuco-tuco) is an herbivorous subterranean rodent that lives in coastal grasslands inside humid burrows that reduce evaporation. However, their osmoregulatory mechanisms may be challenged by atmospheric variations when foraging aboveground and by the annual variability in dietary water and salt content. Then, it is of great interest to identify how much of this flexibility of C .talarum is attributed to physiological regulation. We analyzed the effect of water and salt content of diet on urinary, plasmatic, fecal and respiratory parameters. Tuco-tucos were not able to maintain their body weight under the offered monodiet, especially under the low hydrated diet, which explains its generalist and opportunistic foraging behavior. C. talarum mainly obtained water through food, whereas water metabolic production was negligible. Evaporative water loss did not vary between diets, but individuals under water restriction showed decreased fecal water loss and urine volume, high urine concentration but stable plasmatic osmolality and ionic concentration values. Under salt stress, urinary parameters remained relatively stable and high plasmatic osmolality was detected. Despite C. talarum produced more diluted urine than rodents from xeric environments, it is able to concentrate it 4 times above than the required at field even under the lowest water availability. This may be a characteristic associated with the evolutionary history of the species, which evolved in an arid context.

Digestive flexibility in females of the subterranean rodent ctenomys talarum in their natural habitat

We studied the occurrence of digestive strategies at different levels in females of the subterranean herbivorous rodent Ctenomys talarum living in their natural habitat. We determined the dimensions of different parts of the gastrointestinal tract and organs along as the activity of key digestive enzymes(sucrase, maltase and N-aminopeptidase) in small intestine in females seasonally caught. Females of C. talarum did not show seasonal variations in the mass of the different parts of the gastrointestinal tract. In nonreproductive females large intestine was longer in autumn, whereas reproductive females did not show seasonal variations in the length of the different parts of the gut. Females of C. talarum exhibited a high sucrose, maltase and N-aminopeptidase activity in small intestine, although these activities were higher in small intestine of females caught in autumn (nonreproductive) than in females caught in winter (reproductive). The results show that C. talarum females exhibit characteristics in the gut at the morphological and biochemical level, which could represent digestive strategies to face the constraints imposed by their costly particular way of life.

The allometry of rodent intestines

This study examined the allometry of the small intestine, caecum, colon and large intestine of rodents (n = 51) using a phylogenetically informed approach. Strong phylogenetic signal was detected in the data for the caecum, colon and large intestine, but not for the small intestine. Most of the phylogenetic signal could be attributed to clade effects associated with herbivorous versus omnivorous rodents. The herbivorous rodents have longer caecums, colons and large intestines, but their small intestines, with the exception of the desert otomyine rodents, are no different to those of omnivorous rodents. Desert otomyine rodents have significantly shorter small intestines than all other rodents, reflecting a possible habitat effect and providing a partial explanation for the low basal metabolic rates of small desert mammals. However, the desert otomyines do not have shorter colons or large intestines, challenging claims for adaptation to water retention in arid environments. Data for the Arvicolidae revealed significantly larger caecums and colons, and hence longer large intestines, with no compensatory reduction in the length of the small intestine, which may explain how the smallest mammalian herbivores manage to meet the demands of a very high mass-specific metabolic rate. This study provides phylogenetically corrected allometries suitable for future prediction testing.