Sunday, 28 June 2015

Unexpected social behaviour in South American Opossums.


Many species of Placental Mammals are highly gregarious, often exhibiting complex social structures. Such behaviour is much more unusual among Marsupials, with some Australian species living in small colonies with limited social interaction, and occasionally forming larger ‘mobs’ under certain conditions, and almost no social interaction known among American Marsupials. Most American Opossums, Didelphidae, live more-or-less totally solitary lives as adults and under most circumstances are hostile towards co-specifics (members of the same species). Opossums can learn to tolerate one-another in captivity (though they usually do this by ignoring one-another), but examples of social interaction in the wild are very rare. Juveniles, as with all Mammals, live with their mothers until close to maturity, and in some species sub-adult siblings have been shown to continue to live together for short periods after the mother has left the communal nest. Some species also show extended mating periods, with males and females remaining together for several days prior to mating (though interactions can be fairly aggressive during this period). However the fossil Dideplphid Pucadelphys andinus, which lived in the Palaeocene, appears to have been far more social, and to have lived in larger groups, suggesting that Opossums have not always been solitary animals, and that such behaviour could be occurring unrecorded in modern members of the group.

In a paper published in the journal Biology Letters on 17 June 2015, Diego Astúa, Rafael Carvalho and Paula Maia of the Laboratório de Mastozoologia at the Universidade Federal de Pernambuco, Arthur Magalhães of the Laboratório de Mamíferos at the Universidade Federal da Paraíba and Diogo Loretto of the Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios describe the results of a study of the utilization of artificial nest boxes by Opossums in Brazilian Atlantic forests and urban sites on the campus of the Universidade Federal de Pernambuco which revealed several unexpected examples of social behaviour.

Astúa et al. came across ten examples of cohabitation, or close association, among five species of Opossums in Atlantic forest close to Rio de Janeiro. In the first a pair of Brazilian Gracile Opossums, Gracilinanus microtarsus, comprising an adult male and a subadult female were found cohabiting a nest box at the start of the mating season. In the second a pair of Tate's Woolly Mouse Opossums, Marmosa paraguayana, again comprising an adult male and a subadult female, were also found cohabiting in a nest box at the start of the mating season. In the third three juvenile Bare-tailed Woolly Opossums, Caluromys philander, two females and a male were found in the same nest box at the end of the breeding season; DNA testing revealed these to be siblings. In the fourth two juvenile female Big-eared Opossums, Didelphis aurita, were also found cohabiting a nest box at the end of the breeding season; these were not DNA tested, but are thought likely to have been siblings. In the fifth instance two subadult female Gray Slender Opossums, Marmosops incanus, were found sharing a nest box at the end of the breeding season. The six the instance also involved a pair of subadult Gray Slender Opossums cohabiting at the end of the breeding season, though in this case they were a male and a female. The seventh example a pair of adult Gray Slender Opossums were found cohabiting in a nest box at the end of the mating season, again a male and a female. The eighth case involved a pair of adult Bare-tailed Woolly Opossums, a male and a female, found cohabiting at the end of the mating season, in this case the female had four newborn infants in her pouch. The ninth example comprised two adult Bare-tailed Woolly Opossums of unknown sex found together in a nest box at the end of the mating season. The tenth case involved two adult female Opossums of different species, one Tate's Woolly Mouse Opossum and one Bare-tailed Woolly Opossum found nesting in close association (nests about 2.5 m apart within the same tree) during the mid-breeding season.

However the most remarkable discovery came at the Universidade Federal de Pernambuco campus, not within a nest box, but in a nest constructed within an electrical connection box, to which the team were called by university maintenance staff. Here a total of 13 White-eared Opossums, Didelphis albiventris, were found cohabiting within a den. All the animals were awake when investigated, and showed no sign of hostility towards one-another. The group comprised at least three adults, plus several sub-adults and juveniles. One of the adults sought to protect the juveniles and subadults during removal.

Specimens of Didelphis albiventris found in a communal den at Universidade Federal de Pernambuco campus, Recife, Brazil. At least nine specimens (out of a total of 13) of different sizes can be seen on the photo. Astúa et al. (2015).

See also…

The One-striped Opossum, Monodelphis unistriata, was described as a species by JA Wagner from a skin and skull of an adult male animal, brought back from Brazil by the explorer Johann Natterer in 1821, which...

Modern Australian Marsupials are generally held to be a distinct evolutionary lineage, distinct from South...



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