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Diet
Diet consists mainly of insects, but fortified by frugivory – although their digestive system can’t properly handle the fibrous material found in most fruits, they will chew the fruit to obtain as many nutrients as possible, and later spit out the fiber and other indigestible components,. They use their snout to peruse the undergrowth for arthropods, fruit, and.

Habitat
Tree shrews are localized almost exclusively to the tropical rainforests of southeast Asia, most prominently in Thailand, Indonesia, Sumatra, Java, and other Polynesian islands. While they are tree-dwellers, they spend much of their time on the ground foraging for food on the forest floor. They are agile climbers, often exploring large vertical trees and bushes for food and nesting material.

Predation
Birds of prey, snakes, and small carnivores have been known to hunt Tupaia. Humans have no interest in killing tree shrews for food because of their unpleasant taste, and unlike other small mammals, Tupaiaare rarely seen as pests.

Description
They have slender bodies and limbs, and curved, sharp claws. Their ears and eyes are large, contributing to their keen senses of hearing and sight (6). Their body size ranges from 11-22cm long with tails ranging from 13-22cm. They have dense fur, ranging in color from reddish orange to gray, brown and black with back or shoulder stripes or facial markings to distinguish different species. While most are completely fur covered, the pen-tailed tree shrew has a naked tail with only a tuft of hair at the very tip.

Phylogeny
Tupaia retain many primitive characteristics known of the earliest true mammals, and have been classified in the sub-order Prossimi of the Primates order, despite many similarities to rodents and insectivores. Other classifications have placed them in their own mammalian order, Scadentia, under the genus Tupaia. Their morphological similarity to primates makes them an important model organism in human medical research. One outstanding characteristic of tupaia is their color vision. Most subprimate animals, including rodents and squirrels that tupaia are often associated with, lack the adaptation of well-developed color vision. However, research has shown that tupaia have rod and cone visual receptors similar to primates and humans. Tupaia differ from other endotherms in their body temperature regulation: there is more variance during the circadian rhythm during the day, suggesting that the regulation of body temperature is synchronized to the rhythm of locomotor activity.

Pen-tailed tree shrews demonstrate another fascinating adaption – the ability to daily consume alcohol at concentration levels of up to 3.8 percent! The flowers of the bertam palm (Eugeissona tristis) produce nectar which contains one of the highest alcohol concentrations of all natural foods. Pen-tailed tree shrews frequently consume this nectar while showing no signs of intoxication. Since pen-tailed tree shrews are considered a primitive ancestor for all tree shrews and primates, the ability to ingest high amounts of alcohol is hypothesized to have been an evolutionary adaptation in the phylogenic tree. However, it is unclear how the pen-tailed tree shrews benefit from this alcohol ingestion or what consequences of consistent high blood alcohol content might factor into their physiology.

Reproduction and Development
Tree shrews share more similarity with rodents and squirrels than with primates in regards to their reproduction and development. In contrast to primaters, who produce one baby with longer gestation periods, tree shrews generally have litters of 2-3 young and are only in utero for about 45 days. Female tree shrews give birth in nests made of many dry leaves, and are known to leave the young unattended while returning occasionally to give them milk. Parental care of tupaia is relatively limited. The young remain in the nest for 33 days on average, developing gradually before they exit the nest. There are ten identified embryonic developmental stages in tupaia. Baby tree shrews are sexually immature until about 90 days after birth. Tree shrews are territorial animals. Usually, only one male and one female tree shrew live in the same spatial region, although at times one male can interact with two females. Males protect territory with scent markings, and will chase other males from their territory while females chase other females from their territory.

Use as a Medical Model
Since tupaia share so many similarities with primates yet are more abundant and have more plentiful progeny than them, there is increasing interest in using tupaia as an alternative model for use as a model in human medical research. Successful psychosocial studies have been done, and it was found that dramatic behavioral, neuroendrocrinal, and physiological changes occurred in subordinate male tupaia, similar to depressed human patients. Tupaia’s susceptibility to viruses have also piqued interest in using them to study immune responses to infections such as hepatitis B. Tupaia have been used to overcome the limitations of using rodent models in the study of human biology, disease mechanisms, and development of new drugs and diagnostic tools. Recent studies have utilized tree shrews to study infectious, metabolic, neurological, and psychiatric diseases as well as cancers.

In 2013, an article was published in Virology Journal documenting the use of Tupaia belangeri as medical models for the H1N1 virus. This was advantageous because other possible candidates for study (guinea pigs, rats, mice, and others) leave gaps in the information especially regarding clinical symptoms and transmission. Tupaia, on the other hand, display moderate systemic and respiratory symptoms as well as pathological changes in the respiratory tract, supporting its use as a beneficial model in H1N1 research.

Another instance has been documented where an individual of Tupaia glis developed breast cancer. A study investigating the effects of the Borneo disease virus on tree shrews has given new insight into neurological disease. As knowledge increases regarding the use of tree shrews as medical research models, it will be essential to consider the ethical implications. Although tree shrews are abundant in Southeast Asia and endangerment is not a critical issue at this time, it is imperative that legislation regarding the humane treatment of these animals be enforced, and consideration given towards how a change in the Tupaia species population will affect their ecological environment.