Didelphis aurita
Big-eared Opossum
Description:
Didelphis aurita was long considered a subspecies of Didelphis marsupialis,
however recent DNA evidence places Didelphis aurita as its own species. Qualitatively
the differences between the two are lacking and indistinguishable. Didelphis aurita and
Didelphis marsupialis have undergone divergence at both the DNA and morphometric
levels, but qualitative aspects of their skull morphology appear unchanged. DNA
sequence data has shown a divergence of 2.9% in kimura two-parameter distance at the
mitochondrial cytochrome b gene of Didelphis aurita and Didelphis marsupialis
specimens each taxon being monophyletic (Cerqueira and Lemos 2000). Didelphis
marsupialis and Didelphis aurita are not known to overlap in geographic range, so the
site of location can be used for preliminary identification (Emmons 1997).
Didelphis aurita has a well-developed black centerline on its forehead. The
underfur is described as a dirty yellow color with the overhairs being black or grey. The
ears are black and the tail is furred at the base as long as the hind leg, with black and
white parts nearly of equal length, or sometimes the black parts being longer (Emmons
1997). Average body mass of Didelphis aurita ranges from 670-1560 grams. The tail
length typically is around 31.72 cm with and average claw length of 0.47 cm (Vieira
1997). Opossums usually have around 50 teeth with a dental formula I 5/4, C 1/1, P 3/3,
M 4/4 = 50. They have five digits on each foot with a hind foot that has an opposable
thumb. The rostrum is long, ears and tail are naked, with the tail being highly prehensile
(Eisenberg and Redford 1999).
Distribution:
Didelphis aurita occurs in Brazil, Paraguay, and Argentina (Ventura etal 2002).
Didelphis aurita occurs from coastal Brazil from Bahia to Rio Grande do Sul, west to the
lower Rio Paraguay. They typically occur up to 1000 meters in elevation (Emmons
1997).
-See distribution map.
Ontogeny and Reproduction:
Didelphis aurita is considered insectivorous-omnivorous marsupial and
occasionally eats vertebrates and fruits depending on the availability and the season.
Fossorial invertebrates such as Diplopoda, Opiliones, and Coleoptera are highly preyed
upon. They will eat the fossorial snake Cobra-cega (Liotyphlops beui). The main fruits
consumed where the Passion flower (Passiflora actinia) and Sanctaecatharine nightshade
(Solanum sanctaecatharinae). Most fruits are consumed during the wet season since that
is when the most are available. The ability of Didelphis aurita to climb may explain the
high fruit occurrence in its diet (Santori etal 1996).The Rufous-bellied Thrush (Turdus
rufiventris) is the highest consumed vertebrate in their diet, but the Parana Grass mouse
(Akodon paranaensis) and Black-footed Pygmy rice rat (Oligoryzomys nigripes) are
frequently consumed rodents (Caveres and Monteiro-Filho 2001). Santori etal (1996)
found the Collared lizard (Tropidurus torquatus) to be their most frequent prey.
Typically, Didelphis aurita will produce 2-3 litter per year (Eisenberg 1999). The
average litter size in eastern Columbia is 6.5. Breeding season begins in January after 4
months of anestrous and first litters are weaned in April and replaced by the second,
which are weaned at the close of the reproductive season in August. Males usually
include at least 3 females in their home range (Tyndale-Bisoe and Mackenzie 1976).
Didelphis aurita frequently nests in tree cavities (Miles etal 1981).
Gestation lasts 13-14 days for South American species. They have yolk-sac
placentas. After the young are born, they climb unassisted to the nipple area, where the
mother will transport the entire litter attached to her teats for the first 5 or 6 weeks of
their development. Following this, the young detach and begin the nest phase where the
mother will not continually transport them, but will come back to the nest to nurse
(Eisenberg and Redford 1999).
Ecology and Behavior:
Opossums are opportunist feeders and will commonly shift their home range to
adapt to fluctuating resources. They are typically found in moister habitats (Eisenberg
and Redford 1999). Didelphis aurita inhabits humid tropical lowland forests (Emmons
1997). Female home range is around 0.2 ha in the dry season and even less during the wet
season. Males have a typical home range of 3.0 ha in the wet season (Caveres and
Monteiro-Filho 2001).
Didelphis aurita showed to have the greatest frequency of movements in the
range of 0-20 meters. In a study done by Gentile and Cerqueira, (1995) 61% of their
movements were less than 60 meters. They also did not see males as being more nomadic
than females, as Caveres and Monteiro-Filho (2001) observed in a study in Southern
Brazil, however some females did have longer residence time than males (Gentile and
Cerqueira 1995).
Didelphis marsupials do not typically exhibit territoriality, however female
Didelphis aurita are territorial during the wet season when they are reproductively active.
There main activity period was the first hours of the night. Caveres and Monterio- Filho
(2001) suggested opossums may direct some of their foraging activity to capture
crepuscular living prey.
Opossums are solitary and antisocial animals and usually avoid one another or act
aggressively. When two males meet there is almost always extreme agonistic behavior.
Two opposite sexes meeting during the breeding season will initially be aggressive, but
usually turns into courtship, and the two animals may spend several days together. If a
male is placed with a female that is not in estrous, she becomes aggressive, but the male
does not return her attacks (Nowak 1991).
Literature Cited:
Caveres, N.C. and E.L.A. Monteiro-Filho. 2001. Food habitats, home range and activity
of Didelphis aurita (Mammalia, Marsupialia) in a forest fragment of southern Brazil.
Studies on Neotropical Fauna and Environment 36: 85-92.
Cerqueira, R. and B. Lemos. 2000. Morphometric differentiation between neotropical
Black-eared opossums, Didelphis marsupialis and D. aurita (Didelphimorphia,
Didelphidae). Mammalia 64:319-327.
Eisenberg, J.F. and K.H. Redford. Mammals of the Neotropics. Volume 3. 1999. The
University of Chicago Press, Chicago, Illinois, USA.
Emmons, L.H. Neotropical Rainforest Mammals. 2nd Edition. 1997. The University of
Chicago Press. 14-16.
Gentile, R. and R. Cerqueira. 1995. Movement patterns of five species of small mammals
in a Brazilian restinga. Journal of Tropical Ecology 11:671-677.
Miles, M.A., A.A.DeSousa and M.M. Povoa. 1981. Mammal tracking and nest location
in the Brazilian forest with and improved spool-and-line device. Journal of Zoology 195:
331-347.
Nowak, R.M. Walker’s Mammals of the World. 5th Edition, Volume 1.1991. John
Hopkins University Press. 19-20.
Ventura, J. etal. 2002. Morphometrics of the genus Didelphis ( Didelphimorphia:
Didelphidae) in Venezuela. Journal of Mammalogy 83:1087-1096.
Vieira, M.V. 1997. Body size and form in two neotropical marsupials, Didelphis aurita
and Philander opossum (Marsupialia: Didelphidae). Mammalia 61: 245-254.
Santori, R.T. etal. 1996. Diet composition of Metachirus nudicaudatus and Didelphis
aurita (Marsupialia, Didelphoidea) in southeastern Brazil. Mammalia 60:307-311.
Tyndale-Biscoe, H. and R.B. Mackenzie. 1976. Reduction in Didelphis marsupialis and
D. albiventris in Colombia. Journal of Mammalogy 57:249-265.
Reference written by Scott Williams, Biology 378 student. Edited by Christopher Yahnke.
Page last updated 08-03-05.