MONITO DEL MONTE: Microbiotheria

PHYSICAL CHARACTERISTICS

The common name monito del monte is Spanish for "little monkey of the mountain." The "monkey" aspect of the common name derives from the animal's nearly furless, somewhat monkey-like hands and feet. Another local common name for the species is colocolo. The scientific name of this species has recently been changed to Dromiciops gliroides, and the species may be referred to as Dromiciops australis even in recent writing.

As with the other living New World marsupial orders, the single living species of Microbiotheria is a remnant with a more diverse past. The fossil record has revealed an extinct genus, Microbiotherium, with six known species, that thrived during the Oligocene and Miocene Epochs (thirty-four million years ago to five million years ago, for a period of thirty-nine million years). Today, D. gliroides represents an order with only a single living species.

An adult monito del monte's size is between a rat's and a squirrel's. The head-and-body length runs 3.3 to 5 inches (8.3 to 13 centimeters). The tail length is about the same, running 3.5 to 5 inches (9 to 13.2 centimeters), The adult body weight runs about a half ounce to just over one ounce (16.7 to 31.4 grams). The animal's coat of fur is fine, short and thick. The upper body pelt is brown, with several light gray patches or spots on the shoulders and rump. The face fur is gray, the large eyes encircled with prominent black rings. The belly fur is pale tan.

The tail is completely furred, except for a furless area, about an inch long (2.5 to 3 centimeters), on the underside, at the

MONITOS AND MISTLETOES

The thousand-or-so species of mistletoe are distributed over most of the world, including the moist temperate forests of southern South America. Mistletoes are hemiparasites, meaning partly parasitic. Although they have green leaves for photosynthesis, they live on tree branches and trunks, anchoring themselves and tapping into the wood to steal nutrients and water from the host tree. In most species of mistletoe, the seeds are spread by birds, which eat the seeds and defecate (DEF-uh-kate) them later while roosting. If they void the seeds while roosting on a tree branch, the seeds, covered with a gluey substance called viscin (VIS-in), are likely to stick to the branch and grow up to be mistletoes.

In an exception to the habit of birds being the main vectors, or transporters, for mistletoe species, the monito del monte feeds and disperses seeds of the mistletoe species Tristerix corymbosus. In fact, the little marsupial, as far as anyone knows, is the only disperser of the seeds of this mistletoe species. This was discovered by Guillermo Amico and Marcelo Aizen of the National University of Comahue, Argentina. During field studies, they came across numerous strings of mistletoe seeds sticking to the trunks of host trees. They were seeds of T. corymbosus, the fruits of which are green when ripe. Normally, green color in fruits indicates that they are not yet edible, so that fruit-eating birds will pass them up. The large number of T. corymbosus strings glued to tree trunks was also unusual, since birds defecate mistletoe species' seeds while roosting on tree branches. Only some of the seeds end up on branches and grow, and birds have no special ability to aim for tree trunks.

On the other hand, some mammal species consume ripe green fruit. That known fact and the sight of lots of mistletoe seeds on tree trunks indicated an arboreal, or tree-living, mammal as the seed-eater and disperser. Further searching and observing revealed that mammal to be the monito del monte. The species gorges on the mistletoe fruit. The animals peel the rinds off the fruit with their front paws, swallow the innards whole, seeds and all. Soon after a meal of mistletoefruits, the marsupial defecates almost all the seeds, undamaged by the animal's digestive system, in and on its foraging territory, which includes tree trunks and branches.

tip. The one-third of the tail closest to the body has the same sort of dense, woolly fur as the body, while the rest of the tail has straight, dark brown fur. The female's well-developed pouch is comfortably lined with light brown fur and has four nipples. The ears are moderately furred.

As in many small marsupials, the snout is conical, cone-shaped, and tapering, but shorter than is usual among marsupials.

GEOGRAPHIC RANGE

The monito del monte has a limited range in South America, in southern Chile, overlapping into Argentina, from Concepción, Chile, southward to and including the Chilean island of Chiloé, and inland to the Andes and just over the border into Argentina.

HABITAT

Monitos del monte live in dense, cool, temperate rainforests, in the lowlands and the Andes mountains, from sea level to 6,000 feet (1,850 meters) above sea level. They most often live in thickets of Chilean bamboo (Chusquea species), especially Chusquea valdiviensis, the most common ground plant in these forests.

The forest type where the monito del monte makes its home is as unique as the animal itself. Called Valdivian temperate forest, it is located in a limited range in southern South America between the Andes and the Pacific Ocean, most of it in Chile with some extending into Argentina. The Valdivian forest biome is isolated from the rest of the world by deserts, mountains, and oceans. The forest is a treasure house of ancient plants and animals, some of which date back, little changed, from the time when the southern continents were all attached together, forming the ancient supercontinent of Gondwana. The Valdivian forests have been in their present isolated condition for thirty million years. A full 90 percent of the seven hundred flowering plant species there are endemic, meaning they are found no where else in the world. One third of the woody plants (trees, shrubs, woody vines) have living relatives in Australia, New Zealand, New Caledonia (an island northeast of Australia), and Tasmania, all linking to an ancient common landmass. The monito del monte is a living fossil whose relationship with other marsupials shows the same sort of geographic split as do the Valdivian plants.

DIET

The monito del monte is mostly insectivorous, meaning that it forages for and eats insect larvae (LAR-vee) and pupae (PYOO-pee). They also eat some plant material. They do most of their foraging at night, in the trees and on the ground. In the Southern Hemisphere in autumn, the animals gorge, doubling their body weights in a week, most of the extra weight being fat packed into the base of the tail.

BEHAVIOR AND REPRODUCTION

Colocolos are solitary, nocturnal foragers, both in trees and on the ground. They build and shelter in globe-shaped nests of sticks and water-repelling Chusquea bamboo leaves, lined with moss and grass, in protected areas, and often concealed by a final overlay of gray moss. The nests are about 8 inches (20 centimeters) in diameter. Nest locations may be rock clefts, hollows of trees, or in dense ground shrubbery. The nests are snug and comfortable, but in the coldest months, monitos del monte hibernate, living off fat reserves in the base and first third of the tail.

Since monitos del monte are marsupials, birth and nurturing of the young follow the standard marsupial model: the young are born at an incomplete stage of embryonic development, crawl from the birth canal over the mother's belly fur to the pouch, and there latch onto nipples and remain so, nourished by milk, until they complete their development.

Colocolos mate in the Southern Hemisphere spring and early summer—October through December. A female has a single litter of one to four young annually. Litters of five young have been seen, but since the mother has only four nipples, the fifth cannot survive. On leaving the pouch, the young first reside in the nest, then ride on the mother's back, clinging to her fur as she forages, before beginning to forage on their own. The offspring live solitary lives but continue to associate, off and on, with the mother. The young of both sexes reach sexual maturity in two years. Males remain with females only during the breeding season. The maximum lifespan of this species is probably three to four years.

Colocolos hibernate, intermittently, in their nests, during the cool and cold months, depending on temperature and food availability. Torpor, the low state of body activity in hibernation, is triggered by absence of food over time or by outside temperature. A torpor bout, or period of lowered body functions, may last a few hours to several days (five days is the longest known bout period). Hibernating colocolos rouse themselves spontaneously, probably cued by a temperature increase in their surroundings or a signal from some internal clock. These periods of hibernation, along with the stored tail fat, enable the colocolo to conserve body energy while waiting out periods of low food availability and cold.

MONITOS DEL MONTE AND PEOPLE

There is little interaction between these small, secretive animals and humans. In the Lake Region of Chile, a superstition holds that seeing a monito del monte in the home brings bad luck, and that the only cure is burning down the house. One the other hand, the animal's consumption of insects serves as a local control on insect populations.

Scientific value of the monito del monte is immense, because of its ancient origins and relationships.

CONSERVATION STATUS

Monitos del monte are listed as Vulnerable, facing a high risk of extinction in the wild, on the Red List of the World Conservation Union (IUCN). The main problem facing the species is ongoing deforestation.

FOR MORE INFORMATION

Books:

Aplin, K. P., and M. Archer. "Recent Advances in Marsupial Systematics With a New Syncretic Classification." In Possums and Opossums: Studies in Evolution. Vol. I. Chipping Norton, U.K.: Surrey Beatty and Sons PTY Limited, 1987.

Feldhamer, G. A., L. C. Drickamer, S. H. Vessey, and J. F. Merritt. Mammalogy: Adaptation, Diversity, and Ecology. Boston: WCB McGraw-Hill, 1999.

Szalay, F. "A New Appraisal of Marsupial Phylogeny and Classification." In Carnivorous Marsupials. Sydney, Australia: Royal Zoological Society of New South Wales, 1982.

Vaughan, T. A., J. M. Ryan, and N. J. Czaplewski. Mammalogy, 4th ed. Philadelphia: Saunders College Publishing, 2000.

Periodicals:

Amico, G., and M. A. Aizen. "Mistletoe Seed Dispersal by a Marsupial." Nature no. 408 (2000): 929–930.

Bozinovic, Francisco, G. Ruiz, and M. Rosenmann. "Energetics and Torpor of a South American "Living Fossil," the Microbiotheriid Dromiciops gliroides." Journal of Comparative Physiology B 174 (2004): 93–297.

Hershkovitz, P. "Ankle Bones: The Chilean Opossum Dromiciops gliroides Thomas, and Marsupial Phylogeny." Bonner Zoologische Beiträge no. 43 (1992): 181–213.

Hershkovitz, P. "Dromiciops gliroides Thomas, 1894, Last of the Microbiotheria (Marsupialia), With a Review of the Family Microbiotheriidae." Fieldiana Zoology (New Series) 93, no. 1502 (2004).

Kirsch, J. A. W., A. W. Dickerman, O. A. Reig, and M. S. Springer. "DNA Hybridisation Evidence for the Australian Affinity of the American Marsupial Dromiciops australis." Proceedings of the National Academy of Science, USA no. 88 (1991): 10465–10469.

Marshall, L. G. "Dromiciops australis." Mammalian Species 99 (1978): 1–5.

Pridmore, P. A. "Locomotion in Dromiciops australis (Microbiotheriidae)." Australian Journal of Zoology no. 42 (1994): 679–699.

Westerman, M., and D. Edwards. "The Relationship of Dromiciops australis to Other Marsupials: Data From DNA-DNA Hybridisation Studies." Australian Journal of Zoology no. 39 (1991): 123–130.

Horovitz, Inez, and M. R. Sánchez-Villagra. "A Morphological Analysis of Marsupial Mammal Higher-Level Phylogenetic Relationships." Cladistics19, no. 3 (June 2003): 181–212.

Web sites:

Terrestrial Ecoregions—Valdivian temperate forests (NT0404). http://www.worldwildlife.org/wildworld/profiles/terrestrial/nt/nt0404_full.html (accessed on June 29, 2004).

Animal Diversity Web, University of Michigan. http://animaldiversity.ummz.umich.edu/site/index.html (accessed June 29, 2004).