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Monodelphis kunsipygmy short-tailed opossum

By Marcin Rejniak

Geographic Range

Pygmy short-tailed opossums are a very poorly known species. Not many specimens of this mysterious mammal have been collected (about 15 individuals total); the are from Bolivia (seven) and the rest from Brazil and Argentina. However, the range of Monodelphis kunsi probably extends to Peru since the reported collection sites were in close proximity to the national borders of this country. The first type specimen of this opossum was collected in Bolivia at "La Granja" near the west margin of Itonamas River, 4 km north of Magdalena (13° 18' S, 64° 09'W) at approximately 200 m of elevation. In Argentina, the first specimen of Monodelphis kunsi was collected quite recently (2005) at 22° 18' 41.4'' S, 63° 58' 7.1''W, 700 m above sea level. (Anderson, 1982; Jayat and Miotti, 2005; Salazar, et al., 1994; Vargas, et al., 2003)

Habitat

Not much is known about the preferred habitat of Monodelphis kunsi. Based on the topography of the sites from which the specimens were collected, it appears that M. kunsi occupy a wide range of terrestrial habitats. Locations from which the specimens were collected are characterized by a wide range of elevations, from 200 m to 1500 m. One specimen of the pygmy short-tailed opossum was collected in an area with thick brush, many rocks and fallen wood, and ground covered by occasional small forbs and ferns. The ground was steeply sloped (30°) and there was about 10 to 12 cm layer of mulch and litter. In contrast, another specimen was collected in a banana field about 30 m from a river. On this flat terrace with very moist soil and about 2 cm of leaf litter; the trees (7 to 8 m tall) and shrubs combined, provided 30 to 60 % cover. While these two areas represent somewhat moderately disturbed ecosystems, pygmy short-tailed opossums have also been collected in quite pristine habitats. (Anderson, 1982; Salazar, et al., 1994)

  • Range elevation
    200 to 1500 m
    656.17 to 4921.26 ft

Physical Description

Monodelphis kunsi is probably the smallest species in the genus Monodelphis. The mass of specimens lies between 7.5 and 30 grams and length between 103 and 147 millimiters. Monodelphis kunsi lacks a sagittal crest on the skull and enlarged canines. Unlike M. americana and M. brevicaudata, pygmy short-tailed opossums have no dorsal stripes or lateral reddening. M. kunsi have throat glands covered by thin fur. Over the body, the fur of these opossums is short, generally warm brown on the dorsal side and with whitish areas on the ventral side. The tail is bicolored, darker dorsally and buffy ventrally; covered by fine hair, except for the tip which may serve a tactile function. The skull is small (about 22 mm in length) with no postorbital processes and a relatively blunt rostrum. The head is covered with numerous mystacial, genal, supraorbital, and interramal vibrissae. The hind feet have noticeable webs between digits 3 and 4 and a less conspicuous web between digits 2 and 3. All members of the genus Monodelphis lack abdominal pouches. (Anderson, 1982)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    7.5 to 30 g
    0.26 to 1.06 oz
  • Range length
    103 to 147 mm
    4.06 to 5.79 in

Reproduction

Nothing is known about the reproduction of M. kunsi. It is possible that these tiny opossums are promiscuous, similarly to many other members of the family Didelphidae. Generally, species in this group are solitary and interact with each other only for the purpose of mating. (Mandavia and Myers, 2004; Vargas, et al., 2003)

Nothing is known about the reproductive behavior of Monodelphis kunsi. Since M. kunsi are in the infraclass Metatheria (marsupial mammals), they almost certainly have a short gestation period and young fairly undeveloped at birth, as these traits generally characterize this group of animals. (Anderson, 1982; Salazar, et al., 1994)

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

Nothing is known about the type of parental investment in Monodelphis kunsi. As in all mammals, lactating females nourish and protect the developing young. (Anderson, 1982; Salazar, et al., 1994)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The lifespan of Monodelphis kunsi is unknown.

Behavior

Nothing is known about the behavior of Monodelphis kunsi. Like most other Didelphids these opossums are probably solitary except for the mating season. (Mandavia and Myers, 2004; Salazar, et al., 1994)

Home Range

Based on the methods of Rabinowitz et al.(1986) and Arita et al.(1990) for determining rarity, it was established that Monodelphis kunsi has a wide distribution but low densities locally. (Salazar, et al., 1994)

Communication and Perception

Nothing is known about the communication and perception of Monodelphis kunsi. It is possible that this species depends on its sense of touch (numerous vibrissae on the head and feet) and smell as it moves about its environment. Other didelphids rely primarily on their senses of touch, smell, hearing, and, to a lesser extent, sight. (Anderson, 1982; Mandavia and Myers, 2004; Vargas, et al., 2003)

Food Habits

Based on morphological characteristics such as build, size and dentition; which are similar to the members of the family Soricidae, Monodelphis kunsi is probably invertivorous, or possibly omnivorous. The diet of M. kunsi is probably determined by the availability of food resources in a particular area. (Anderson, 1982; Vargas, et al., 2003)

  • Animal Foods
  • insects

Predation

Nothing is known about the predators or anti-predatory behavior of Monodelphis kunsi. These opossums are probably preyed on by mammal carnivores, reptiles, or predatory birds. Their small size and cryptic coloration may help them to evade some predation. (Anderson, 1982; Mandavia and Myers, 2004)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Nothing is known about the role that M. kunsi plays in the ecosystem. These opossums could have an effect on the population sizes of the insects on which they feed. If there is a predator for which M. kunsi is the major food source, it is possible that these opossums could have an impact on population size of this particular predator. (Anderson, 1982; Mandavia and Myers, 2004; Vargas, et al., 2003)

Economic Importance for Humans: Positive

There are no known positive effects of Monodelphis kunsi on humans. (Anderson, 1982; Vargas, et al., 2003; Anderson, 1982; Vargas, et al., 2003)

Economic Importance for Humans: Negative

There are no known negative effects of Monodelphis kunsi on humans.

Conservation Status

According to the IUCN Red List of Threatened Species Monodelphis kunsi is an endangered species due to a decline in area of occupancy, extent of occurrence and/or quality of habitat. Vargas, Tarifa and Cortez (2003) reported that numbers of M. kunsi are declining due to human induced habitat degradation. They estimated that populations declined as much as 50% in the last decade. (Vargas, et al., 2003)

Other Comments

The name Monodelphis is from the Greek word for "single womb" and the specific epithet kunsi honors Dr. Merle L. Kuns who obtained the type specimen. (Anderson, 1982)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Marcin Rejniak (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

insectivore

An animal that eats mainly insects or spiders.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Anderson, S. 1982. Monodelphis kunsi. Mammalian Species, 190: 1-3.

Jayat, P., D. Miotti. 2005. Primer registro de Monodelphis kunsi (Didelphimorphia, Didelphidae) para Argentina. Mastozoologia Neotropical/ Journal of Neotropical Mammalogy, 12/2: 253-256. Accessed February 20, 2006 at http://redalyc.uaemex.mx/redalyc/pdf/457/45712214.pdf.

Mandavia, A., P. Myers. 2004. "Monodelphis brevicaudata (red-legged short-tailed opposum)." (On-line). Accessed March 15, 2006 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Monodelphis_brevicaudata.html.

Salazar, J., M. Campbell, S. Anderson, S. Gardner, J. Dunnum. 1994. New records of Bolivian mammals. Mammalia, 58/1: 125-130.

Vargas, J., T. Tarifa, C. Cortez. 2003. Nuevos registros de Monodelphis adusta y Monodelphis kunsi (Didelphimorphia: Didelphidae) para Bolivia. Mastozoologia Neotropical/Journal of Neotropical Mammalogy, 10/1: 123-131. Accessed February 20, 2006 at http://www.cricyt.edu.ar/mn/indice/pdf/10_1/vargas.pdf.

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