Microbiotheria

Diversity

Order Microbiotheria includes one extant species, monitos del monte ( Dromiciops gliroides ). However, fossil records indicate that this order has included at least 13 other species, separated into 7 genera. Due to the genetic isolation of this species, monitos del monte are of special interest for conservation. This species has many features that may suggest a close relationship with Australian marsupials.

Geographic Range

These animals are found in a narrow range of southern South America, in southern and central Chile and southwestern Argentina. They have been recorded in 88 localities, from the coastal Andes Mountains in Chile, south of Concepcion, to the lowlands of Argentina in the provinces of Neuquen, Rio Negro and Chubut, out to Chiloe Island, from 35 to 43°S south latitude.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

Monitos del monte are found in temperate rainforests dominated by southern beech trees ( Nothofagus ), with a bamboo ( Chusquea ) understory, known as Valdivian temperate forests. These forests are often cool, with a mean annual temperature of 10 to 11°C; they are also damp and humid, with a mean annual precipitation rate of 3,000 to 4,000 mm. These areas may include evergreen and broad leaved forests with vines and epiphytes. On Chiloe Island, these animals are found at sea level, but they may be found at elevations up to 1,600 meters, in Bariloche, Argentina. They may also be found in secondary growth forests, particularly those areas that have bamboo and are open, but they have not been reported in agricultural areas.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• rainforest rainforest
• mountains mountains

Systematic and Taxonomic History

Monitos del monte are the only remaining members of order Microbiotheria . Prior to their characterization as a microbiotheriid , monitos del monte were included in the family Didelphidae . However, several characteristics divide monitos del monte from didelphids including their anklebone articulation, dentition, chromosome morphology and lack of paired sperm. All of these features make monitos del monte dissimilar from all other South American marsupials and similar to Australian marsupials. In fact, these animals are more closely related to Australian marsupials than any other South American marsupial; their relationship is sometimes described as the link between the two groups. The genus name Dromiciops indicates their physical similarities to Australian marsupials, Australian pygmy possums are in the genus Dromicia and the suffix “ops” means “the appearance of”. Prior to their redefinition as microbiotheriids , all members of the family Microbiotheriidae were believed to be extinct. Historically, members of this order had a wider distribution including Bolivia, Brazil and Antarctica. This order may have first appeared in the Mesozoic, the oldest known fossil is from Bolivia. Based on fossil records, basal microbiotheriids likely showed a similar habitat preference to the extant member. This species has previously been known by the name Dromicops australis .

Physical Description

Monitos del monte, the only extant member of order Microbiotheria , are small mouse-sized marsupials, weighing between 16 to 49.5 grams. They have short, silky pelage. Their fur is dense and grayish-brown dorsally and pale whitish ventrally, from their chin to their belly, with a light patch on each shoulder. The back of their neck and the top of their head is reddish-brown, compared to their face, which is largely pale gray. Monitos del monte have white cheeks, with fine whiskers and a dark muzzle. Both eyes have a dark ring, which may extend down to their nose. Directly above their eyes, monitos del monte have a light patch and directly below their ears, they have a dark patch. Their ears are round, small and well-furred. Their bodies and coloration are designed to withstand cool temperatures, with their thick fur, dark coloration and reduced ears. Their total body length is about 195 to 246 mm, including a moderately prehensile tail that measures about 90 to 132 mm. Their tails are used for fat storage beginning at the end of summer, helping them survive times of low food availability, particularly among females. Although there is some debate about the appearance of sexual dimorphism within the species, for at least part of the year, females are larger than males due to their additional fat storage. Females have a well-developed pouch, lined with reddish-brown fur and containing 4 mammae. These animals have large, white hands and feet, which often have furry tufts on their digits, concealing their claws. Monitos del monte have an opposable pollex and hallux. These animals have 50 teeth with spatulate upper incisors and stout canines. They also have extremely enlarged auditory bullae as compared to other marsupials.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

Reproduction

Monitos del monte breed seasonally, and produce one litter per year, this is likely due to the cool winter temperatures in their range. These animals select a mate between August and September. Their breeding season may extend from September to March, ending at the first snowfall and peaking in November.

Monitos del monte likely become reproductively mature when they are 2 years old, or when they weigh between 25 to 28 grams. These animals have a well-developed marsupium that opens ventrally and is lined with soft reddish-brown fur and contains 4 mammae. Often, these animals have litters of 2 to 4 offspring during October through November, after which time, the offspring remain within the pouch and nurse for about 2 months. The young leave the pouch but remain associated with their family group for at least another 2 months.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Females care for their offspring for at least 4 months after parturition, this is the most extended maternal care known among South American marsupials. There is no record of paternal care for this species. Mothers make leafy nests in trees about 1 to 2 meters above ground. Typically, around December offspring leave the pouch, often riding on their mother’s back during nighttime excursions. By the end of February, young may begin independently exploring during nocturnal trips, however, at this point; they remain in close proximity to their mother and use their nest as the center of their home range. Generally, young are independent by March, although females may allow their young to continue suckling until April.

• Parental Investment
• altricial altricial
• female parental care female parental care

Lifespan/Longevity

Currently, the lifespan of monitos del monte is unknown. A wild individual was captured and survived an additional 2 years and 2 months, however, their age at the time of capture was not known.

Behavior

Monitos del monte are nocturnal, arboreal, terrestrial and scansorial. Their activity typically peaks around 2 am and tapers until sunrise. These animals construct round communal nests, about 20 mm in diameter, lined with water-proof bamboo leaves and moss in tree cavities, down trees or in the bamboo understory. Inside their nests, animals mate during breeding season and curl up individually during the rest of the year. In addition to acting as a nesting substrate, bamboo is important for the species because it facilitates their movement and provides shelter. Monitos del monte withstand cool winters in their range through the use of facultative and deep torpor during cold temperatures (around 4.5°C) and times of food shortage. These animals typically remain in a state of torpor for about 2 months, during which time their heart rate falls from 230 beats per minute to about 30 beats per minute. Generally, 21 to 25 individuals can be found per hectare, although their density is lower in their island ranges. Males maintain a home range of about 0.24 hectares, which is significantly larger than the female’s home range size of about 0.15 hectares.

• Key Behaviors
• arboreal arboreal
• scansorial
• nocturnal nocturnal
• motile motile
• hibernation hibernation

Communication and Perception

Monitos del monte are also known by the name Colocolo which originates from the sound they produce, “tzchi-tzchi-kod-kod”. These animals may also produce trills that terminate in a cough and a variety of sounds through their mouths and throats. Likewise, there is evidence to suggest that these animals may have considerable auditory capabilities due to their enlarged auditory bullae. Monitos del monte are known to yield a foul smelling and bad tasting secretion, however, it is unknown whether this acts as a predator deterrent or a mechanism for attracting mates. Their sense of smell is likely of great importance, at least in their first few moments after birth when they must find their way from the cloaca to the pouch.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Monitos del monte are omnivorous animals, feeding largely on insects and fruits. Among invertebrates, these animals mostly consume beetles , grasshoppers and crickets , making up about 43% of their diet. Their insectivorous diet also includes bees, wasps and ants as well as butterfly larvae and pupae. During summer months, when vegetation is more available, these animals also consume fruits and seeds from mistletoe ( Tristerix corymbosus ), hued-hued ( Gaultheria insane ) and quilineja ( Luzuriaga polyphylla ). Monitos del monte are also nest predators of thorn-tailed rayaditos ( Aphrasturna spinicauda ), consuming their young and their eggs. There are also reports of monitos del monte consuming small lizards.

• Primary Diet
• omnivore omnivore

Predation

Monitos del monte use their bamboo habitat to help conceal themselves from predators. They also produce a foul smell that may help repel potential threats. Their remains have been found in the scat of both domestic cats and dogs . These animals are also prey for Chilean long-tailed snakes , among other predators.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Order Microbiotheria serves as an important seed disperser for a variety of rain forest plants. These animals are the only known disperser of a keystone species of mistletoe ( Tristerix corymbosus ), which needs to pass through their digestive tract to stimulate germination. There are also 5 other species for which monitos del monte are the sole seed disperser ( Asteranthera ovate , Cissus striata , Desfontainia spinosus , Luzuriaga sp, Mitraria coccinea ). Monitos del monte also disperse the seeds of 11 additional plants. They may also carry a variety of ectoparasites including ticks, fleas and mites.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Currently, this species offers no economic benefits for humans.

Economic Importance for Humans: Negative

This species poses no real economic threat; however, human superstition regarding the species may be costly. Their presence has been considered a bad omen; this belief has caused humans to set their homes on fire if an animal was seen nearby. A series of inaccurate beliefs has caused a great deal of fear including that they are venomous, cause convulsions and cause phthisis, none of which is accurate. There is also no evidence that these animals are crop or agricultural pests.

Conservation Status

These animals are currently listed as ‘near threatened’ by the IUCN Red List of Threatened Species. Trapping difficulties have made it hard to estimate their population size, although it is believed to be small and declining. These animals are rapidly losing their habitat due to agriculture and logging, likewise introduced animals such as red deer ( Cervus elaphus ), fallow deer ( Dama dama ) and cattle ( Bos taurus ) may also degrade their habitat.

Other Comments

The name ‘monito del monte’ translates to ‘little mountain monkey’. These animals are also known as ‘colocolo’, which refers to the sound they produce.

Additional Links

Encyclopedia of Life

Contributors

Leila Siciliano Martina (author), Texas State University.

References

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