Biology of Other Species

Last modified on June 5, 2010

Tree shrew (Tupaia belangeri)

The tree shrews are the only genus in the order Scandentia. They resemble both primates and rodents. Like prosimians and rodents, they lack bronchial cartilage distal to the lobar bronchi; however, like rodents their terminal bronchioles open abruptly into alveoli. Because they are not technically nonhuman primates, they are not subject to the same regulations, according to Animal Care Policy 7.

In juvenile males, testes descend at 50 days of age; sexual maturity is reached at 3-4 months. Tree shrews have a lifespan of approximately 10 years. An incidental pathologic finding is pulmonary histiocytosis, with traces of cholesterol and fat, and granulomas in the ventral lung lobes.{3819,4094}

They are useful in psychosocial stress research because the males are very territorial. Confrontation with a superior male can cause increased stress hormone levels and temporary retraction of the testicles into the abdomen. Longer duration confrontation may result in profound, irreversible and regressive testicular and epididymic changes. The most common change is hypospermatogenesis (in which the sequence of spermatogenesis is normal up to the level of spermatocytes, but lacking mature spermatozoa). This is statistically related to the application of social stress using an experimental paradigm of allowing two males access to each other for a few hours each day for a month. Testicular atrophy, which is irreversible, is not related to social stress, and occurs significantly more often in the left testicle. In humans, the left testicle descends first and is cooler than the right. Testicular tumors, particularly Leydig cell tumors rather than germ cell tumors, occur at higher frequency than in NHPs (6.3%, whereas only 23 cases in NHPs have ever been reported); in fact they are the most common tumors in male tree shrews >6 years of age. Social stress is known to affect levels of IGF-I, testosterone and LH in NHPs, which has an effect upon germ cell apoptosis.{4094}

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Marsupials

The order Marsupalia contains the New World opossums or Didelphidae, which have been used in research with limited success. The woolly (Caluromys sp), mouse (Marmosa sp), and Virginia (Didelphis virginiana) opossums are some examples that have been used in research. Monodelphis domestica (gray short-tailed opossum) is a newly established model.{3655}

Monodelphis domesticus

Didelphis virginiana

Phascolarcos cinereus (koala)

Macropus eugenii (tammar wallaby)

This is Macropus parryi

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Physiology

Marsupials (metatherians) do not appear to be capable of mounting a mixed lymphocyte response, a measure of T cell function and genetic polymorphisms at the MHC. As a result, they have no immunologic memory and show no isotype switch. Monodelphis domesticus has a high degree of class I polymorphism and rejects allogeneic skin transplants more slowly than eutherian mammals.{4004}{4006}

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Behavior

Other than death-feigning, which has only been reported for one or two didelphid species, the behaviors observed in didelphids are qualitatively similar to those of eutherian mammals. Nevertheless, differences can be seen in prey manipulation and spatial maze behavior. Social interactions appear to be sparser in opossums than in most eutherian mammals. However, the scarcity of systematic research on didelphid behavior still prevents firm conclusions regarding these ancient and interesting mammals.{4079}

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Common Diseases

The most spontaneous disease problems in Monodelphis domestica occur in the digestive system, particularly lesions of the liver. The most common cause of death related to the GI tract is rectal prolapse, largely a female reproductive problem. Neoplasia is most commonly found in the digestive system also (liver followed by pancreas). The kidney is the second most frequently affected organ.{3655} A single case report of intestinal neoplasia with Paneth cell differentiation in a Virginia opossum was published in 1999. This tumor is extremely rare and has been reported in humans with familial adenomatous polyposis.{4078}

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Armadillos (Dasypus spp.)

Armadillos are the natural hosts for Trypanosoma cruzi, Toxoplasma gondii, Sarcocystis, Eimeria, Leptospira, Salmonella, and Mycobacterium leprae. As such, breeding them in captivity would be highly advantageous for research. A group in Brazil claims the best luck with breeding by placing the armadillos in an enclosed area of natural forest. They feed them dog food daily, newborn mice twice a week, crickets and mealworms once a week. They have had one female who raised two offspring followed 1.5 years later by 4 offspring. Armadillos are called xenarthrans. They reproduce by polyembryony to produce identical offspring. D. novemcinctus produces 4 offspring, while D. hybridus produces 12. D. novemcinctus is used because they develop lepromatous leprosy when experimentally infected.{4340}

Comments? Send an email to janet.rodgers@vet.ox.ac.uk