Gracilinanus microtarsus

Geographic Range

Brazilian gracile opossums ( Gracilinanus microtarsus ) are found in southeastern Brazil in coastal rainforests from the Brazilian state of Minas Gerais, south to Santa Catarina. There have also been mixed reports of Brazilian gracile opossums found in Misiones Province, Argentina.

• Biogeographic Regions
• neotropical neotropical
  • native native

Habitat

Brazilian gracile opossums are found in seasonal lowland and pre-montane ecosystems. This species prefers Atlantic coastal rainforests and wet evergreen and deciduous forests in areas of moderate to high rainfall, however, they have also been found on eucalyptus plantations. Brazilian gracile opossums may also be found in cerrado habitats, which are characterized as tropical savannas. These animals are frequently referred to as ‘habitat generalists’, due to their ability to survive in fragmented habitats and human disturbed environments. This species is arboreal and is often found on tree branches and vines, although they forage on the ground. They may use tree hallows, abandoned internal tree nests and bamboo boxes for resting sites.

• Habitat Regions
• tropical tropical

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest
• rainforest rainforest

• Other Habitat Features
• agricultural agricultural

Physical Description

Brazilian gracile opossums are small, pouchless marsupials. These animals have long, uniformly reddish-brown dorsal pelage, with buff gray under fur. Among other members of their genus, Brazilian gracile opossums have notably redder fur than the others. Their faces are noticeably lighter than the rest of their body, with a dark, broad ring around their eyes, reaching their nose. These animals are adapted for an arboreal lifestyle, as shown by the elongated digits on their white feet. Likewise, they have a long, unicolor prehensile tail. Their total body length is about 230 mm, including a tail length of 131 mm, their tail-to-body ratio is 1.25. Their large hind feet are approximately 15 mm long. This species is small and sexually dimorphic. Females typically weigh 20 to 30 grams, whereas males weigh between 30 to 45 grams. Likewise, males grow at a faster rate, about 1.5 times as quickly as females; in addition, their tails, feet and ears tend to be larger. Members of genus Gracilinanus may grow lifelong, these species are short-lived, however, the rare individuals that survive multiple years tend to be noticeably larger. In general, the temperature and metabolic rate of didelphids tends to be lower than similarly sized placental mammals. Female Brazilian gracile opossums in breeding condition tend to have a much higher metabolic rate than those not in breeding condition. Brazilian gracile opossums’ dental formula is as follows: I 5/4, C 1/1, P 3/3, M 4/4 with a total of 50 teeth. Due largely to their range overlap, Brazilian gracile opossums are often mistaken for their relative, agile opossums . In addition to their red dorsal pelage, Brazilian gracile opossums can be distinguished by their larger ears and the broadness of their ocular rings.

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

• Sexual Dimorphism
• male larger

Reproduction

Brazilian gracile opossums engage in a polygynous mating system, similar to other didelphids . The extreme competition among males for breeding females causes a massive amount of stress for this species. As a result, Brazilian gracile opossums are considered partially semelparous because many of the males die shortly after breeding. This trend is considered only partial because each year a few males survive to a second or even third breeding season.

• Mating System
• polygynous polygynous

Brazilian gracile opossums begin mating when they are about 1 year old. This species reproduces seasonally; females are receptive during the end of the cool dry season from August to September. Several pregnant and lactating females have been captured in September to December. Their strategy of synchronous estrous means that their young are born in October to December, during the first half of the warm wet season, when insect prey are most populous. This likely optimizes the female’s ability to capture food while caring for young. Litters are composed of 6 to 14 individuals, with an average of 11 offspring. Weaning begins at about 2 to 3 months of age when the young weigh about 8 to 10 grams.

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

Brazilian gracile opossums are pouchless marsupials. Females typically have 6 to 14 young per litter, but are often found with 8 to 14 young attached. Both attached and unattached young usually stay near their mother; however, older offspring may stay behind in the nest while their mother forages. Females wean their offspring when they are about 2 to 3 months old, during the warm wet season.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

This species has a short lifespan; in general, their life expectancy is about 1 to 2 years. Brazilian gracile opossums are considered partially semelparous; most males do not survive to a second breeding season. Males invest so much in competing for mates that they often show fur loss, poor body condition and are more likely to become infested with parasites after the beginning of breeding season. Although females also have a short lifespan, they survive to a second year more frequently than males. In general, offspring from the preceding season replace the adults each year.

Behavior

Brazilian gracile opossums are solitary and nocturnal; they typically only come together for breeding. However, there may be anywhere from 8 to 29 conspecifics within a given area, these animals may forage in a similar location, but do not interact. This species enters torpor when the ambient temperature is colder than 20°C; although, evidence suggests that they may enter a daily torpor, lasting up to 8 hours. Brazilian gracile opossums are arboreal and have been trapped on tree branches and vines, but also forage on the ground. This species nests in tree hallows, abandoned woodpecker nests and human-made bamboo boxes. These nests are filled with dry leaves and have an internal area for the animals to rest; however, it is unknown whether all animals use these nests or just reproductive females.

• Key Behaviors
• arboreal arboreal
• nocturnal nocturnal
• motile motile
• daily torpor
• solitary solitary

Home Range

Their home range is based on their body size; larger individuals have a larger range. Male home ranges average about 1,400 meters squared and female home ranges average 1,200 meters squared. The difference in home range size between the sexes can possibly be attributed to the larger male body size or to the competition between males for breeding females.

Communication and Perception

There is very little information regarding the communication or perception of genus Gracilinanus . Members of this genus may produce a variety of sounds defensively or when they are startled, these sounds include hissing, growling and screeching. It has been suggested that arboreal marsupials are more vocal and have more adept vision than their non-arboreal counterparts; however, no conclusive studies have been conducted.

• Communication Channels
• acoustic acoustic

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

Food Habits

Brazilian gracile opossums are primarily insectivores; approximately 84% of their diet is composed of insects, of which 35% are beetles (including curculionid , meloid , scarabaeid , alleculid , tenebrionid , chrysomelid , and elaterid beetles). In addition to beetles , stomach content analyses indicate that they also feed on a variety of other insect prey, including termites , ants and wasps , cockroaches , crickets and grasshoppers , moths , dipterans , barkflies , and mayflies . Additionally, they eat snails and fruits from Brazilian nightshade , passion flower and from genus Miconia . They are also important dispersers of seeds from family Araceae .

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• Animal Foods
• insects
• mollusks

• Plant Foods
• fruit

Predation

Brazilian gracile opossums are predated upon by crab-eating foxes , white-tailed hawks , oncillas , maned wolves , margays and jaguarundis . The remains of unidentified members of genus Gracilinanus have also been recorded in the scat of ocelots , coatis and striped owls . Additional predators may include various owls , snakes and lizards .

Ecosystem Roles

Brazilian gracile opossums are insectivores and important seed dispersers for family Araceae . They may become infested with nematodes ( Pterygodermatites jagerskioldi ) and may be parasitized by botfly larvae ( Cuterebra simulans ), especially during the warm wet season. Males are at a much greater risk of parasites after the breeding season begins. Comparatively, Brazilian gracile opossums have relatively few nematodes; this may be because they rarely encounter parasite infested feces due to their arboreal lifestyle.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Brazilian gracile opossums have no known positive impacts on human populations; however, they are important seed dispersers in their habitat.

Economic Importance for Humans: Negative

Brazilian gracile opossums have been found residing in Eucalyptus plantations; however, they are not known to cause any damage.

• Negative Impacts
• crop pest

Conservation Status

Brazilian gracile opossums are currently listed as a species of least concern on the IUCN Red List of threatened species. It is likely that this species has a relatively large population size and can survive in fragmented and human-disturbed habitats.

Additional Links

Encyclopedia of Life

Contributors

Leila Siciliano Martina (author), Texas State University.

References

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