Marmosa isthmica, Goldman, 1912

Russell A. Mittermeier & Don E. Wilson, 2015, Didelphidae, Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona: Lynx Edicions, pp. 129-186 : 137-138

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Marmosa isthmica


9. View Plate 8: Didelphidae

Panama Mouse Opossum

Marmosa isthmica

French: Opossum isthmique / German: Panama-Zwergbeutelratte / Spanish: Marmosa de Panama

Other common names: Isthmian Mouse Opossum

Taxonomy. Marmosa isthmica Goldman, 1912 ,

“ Rio Indio , near Gatun, Canal Zone , Panama.”

Formerly considered a subspecies of M. robinsoni . Monotypic.

Distribution. Panama, W Colombia, and W Ecuador, also in Caribbean lowlands of NW Colombia. View Figure

Descriptive notes. Head—body 11.5-20 cm (males) and 10.5-18.2 cm (females), tail 1625-3 cm (males) and 15-22.9 cm (females); weight 52-143 g (males) and 40-93 g (females). Dorsal fur of the Panama Mouse Opossum is pale to dark orangish, slightly paler on sides of body. Orangish fur continues onto head, where mid-rostral fur is paler and sharply contrasts with that of crown. There is no mid-rostral stripe. Dark brown eye-rings surround black eyes but do not reach base of ears. Tail length is ¢.130% of head-body length, tail has fur on proximal 10% of its length, and naked part of tail is brown, paler on ventral side. Ventral fur is yellowish to orangish, in a streak from chin to anus, with yellowish to orangish gray-based hairs on sides of abdomen. Throat gland is present. Feet are yellowish to orangish-brown, and male Panama Mouse Opossums have a distinct carpal tubercle. Females lack a pouch and have 13 mammae, six on each side, and an additional medial mamma. Its karyotype is unknown. There is no sexual dimorphism in the skull size and shape.

Habitat. Moist lowland and pre-montane forests below elevations of 1700 m. Nevertheless, some specimens of the Panama Mouse Opossum have been collected in dry forests, mangroves, and xeric scrub.

Food and Feeding. Stomach contents of Panama Mouse Opossums collected in the Canal Zone contained ants and other insect remains, fig seeds, and unidentified fruits, with insect remains being the most frequently found items. One trapped individual was observed capturing and eating a butterfly that had entered the trap to feed on the banana bait.

Breeding. In Panama, 1-2 litters were recorded per breeding season, and the Panama Mouse Opossum is believed to be polyestrous. Mean litter size was ten young, ranging from six to 13 young. Although the breeding season is not clearly defined, females that were lactating, pregnant, or had pouch young were found in April-October and December. An adult female kept in the same cage with two young individuals that had been captured far from where she was captured ended up, after some time, “adopting” them. They slept together, and occasionally the young held onto the female’s fur when she moved, as they would with their mother.

Activity patterns. Panama Mouse Opossums are nocturnal and seem to be active right after sunset, although they may start foraging before dark. Some specimens were captured when they were already foraging at dusk, suggesting they left their dens earlier. Others were captured between 16:00 h and 21:00 h.

Movements, Home range and Social organization. In the Panama Canal Zone, individual Panama Mouse Opossums traveled on average 47-59 m, with maximum distances within a trapping grid reaching 103 m. Marked individuals were later recaptured more than 300 m away. Estimated densities in the same area were 31-220 ind/km?.

Status and Conservation. The Panama Mouse Opossum has not been assessed as a distinct species on The [UCN Red List. At the time of the last IUCN assessment, the Panama Mouse Opossum was included as a form of Robinson’s Mouse Opossum ( Marmosa robimsoni ) but was not named or formally assessed as a subspecies. Conservation status of all opossumsis being reassessed by the IUCN New World Marsupial Specialists Group.

Bibliography. Astta (2010), Creighton & Gardner (2007b), Emmons & Feer (1997), Enders (1930), Fleming (1972, 1973), Gardner (2007e), Gutiérrez et al. (2010), Hershkovitz (1992a), Rossi (2005), Rossi, Voss & Lunde (2010), Voss & Jansa (2009), Voss et al. (2014).














Marmosa isthmica

Russell A. Mittermeier & Don E. Wilson 2015

Marmosa isthmica

Goldman 1912