User:Sjh1917/Fat sand rat draft

The fat sand rat (Psammomys obesus) is a terrestrial mammal from the gerbil subfamily that is mostly found in North Africa and the Middle East, ranging from Mauritania to the Arabian Peninsula.

Activity Patterns
The fat sand rat is diurnal, but its activity on the surface fluctuates depending on the ambient temperature. Its period of activity is shortest in the summer, starting in the early morning and finishing an hour to several hours after. As the year progresses and the temperature becomes colder, P. obesus is active for a longer amount of time during the day, and the time that daily activity is initiated is delayed. Upon emerging from their burrows, P. obesus spend a part of the beginning of their day sunbathing, engaging in other activities such as foraging afterwards. A large body mass is an adaptive trait in P. obesus, as individuals with greater body masses have been found to forage for longer periods of time than those with a smaller body mass. When foraging, P. obesus cut pieces away from plants and bring them back to their burrows, where they either eat the plant in the burrow or around the entrance, or store the plant for later consumption. The fat sand rat is atypical in its exploratory behaviour, since when it encounters a novel environment it exhibits perimeter patrolling behaviours, moving in straight lines along the border of an environment, rather than looping or home base behaviours usually displayed by rodents. Males also spend more time exploring an area than females. P. obesus are not social animals, they live in separate burrows with males occupying larger ranges of space than females. Typically, members of the same sex avoid interacting, and members of opposite sexes interact with each other in an agonistic manner.

Habitat Selection
This species usually lives in sandy deserts, but may also be found in rocky terrain or saline marsh areas. It lives in burrows, primarily selecting burrowing sites based on the abundance of Chenopod shrubs in the area rather than other factors such as cover. As such, their preferred type of habitat changes throughout the year in response to the different growing season of plants in the wadi beds or terraces that they inhabit. Distribution of the fat sand rat in a particular habitat is also influenced by the abundance of rainfall in the area, as well as the population density of the site from the previous season. The burrowing activities of the rodents can impact their habitat, affecting the bacteria in the soil around their burrows such that nitrogen fixation and denitrification activity are decreased. The fat sand rat also disturbs vegetation cover while burrowing, further altering its environment. Mounds of active burrows have significantly less percent cover from vegetation than abandoned burrows and undisturbed land near abandoned burrows.

Reproduction
The fat sand rat breeds from autumn to early spring and produces litters usually comprised of one to eight pups, with average litter sizes increasing over the course of the breeding season. When mothers start lactating, their body energy increases but towards the end of the lactation period they begin to utilize stored energy instead of increasing body energy, resulting in a decrease in body mass. The growth rate of pups is maximized when the litter is small and the mother eats plants with a higher water content. The young disperse from their mother at about 5 weeks of age. The sexual activity of male P. obesus is not affected by weather conditions, however there is a correlation between rainfall and the sexual activity of females, with more females becoming sexually active as the amount of rainfall increases. Reproductive strategies differ between the sexes, with females utilizing smaller ranges of space around their burrow with adequate food resources to provide for their young, while males occupy larger home ranges that overlap with multiple female ranges, creating the potential to mate with several females.

Medical significance
Although they remain lean when fed their natural, vegetable-based diet, fat sand rats can easily become obese and acquire type 2 diabetes mellitus when they are fed a normal rodent diet of grains. Therefore, they have been used as an animal model for studies on diabetes and obesity. Sequencing of the complete nuclear DNA genome of Psammomys obesus showed that the Pdx1 homeobox gene, a transcriptional activator of insulin, has undergone massive nucleotide change, likely contributing to diabetes and adaptation to low caloric intake.

Because they are diurnal, fat sand rats are also used as models for human seasonal affective disorder.

Leischmania kDNA has been discovered in P. obesus using molecular studies, suggesting the species can host the parasite that causes leishmaniasis in humans.

These animals have been studied extensively for their remarkably efficient kidneys: they can produce very concentrated urine which enables them to eat halophyte plants and survive extreme heat and lack of water in their desert habitat.