Diversity
Didelphidae
is the largest family of marsupials in the Americas and the only family in order
Didelphimorphia
; it represents 19 genera and 95 species. These animals have fairly diverse modes
of locomotion including terrestrial, arboreal, scansorial and semi-aquatic. Although
members of family
Didelphidae
may range from 10 g to over 2 kg, their size and physical diversity may be limited
by their early developmental requirements. These animals are characterized by their
long rostrum, low body, well-developed sagittal crest and polyprotodont incisors;
their very generalized body plan is considered ancestral for metatherians.
Didelphids
can have a chromosomal diploid number of 14, 18 or 22, although 22 is most common.
Geographic Range
Family
Didelphidae
has a wide geographic range throughout the Nearctic and Neotropical zones. These
animals can be found throughout North, Central and South America and may also be found
on the surrounding continental shelf and Caribbean islands. The northernmost species,
Virginia opossums
, are the only extant
didelphid
found north of Mexico. Since the arrival of Europeans,
Virginia opossums
have expanded their northern range into southwestern Ontario, Canada. The southernmost
species,
Patagonian opossums
, are found into Santa Cruz, Argentina.
- Biogeographic Regions
- nearctic
- neotropical
Habitat
Didelphids
can be found in a wide range of habitats. These animals may survive in dry environments,
tropical forests, grasslands, mountains, temperate forests and near human settlements.
In some cases, human settlement may even facilitate range expansion.
Virginia opossums
have expanded into southern Canada since European settlement, partially due to the
increased shelter and food provided by human habitation. Likewise, other species such
gray four-eyed opossums
and
common opossums
may supplement at least part of their diet with garbage produced by humans. Although
these animals may survive in a wide variety of habitats, their northward expansion
is limited by cold temperatures and deep snows. These animals may be found from sea
level up to 3,400 m in elevation.
- Habitat Regions
- temperate
- tropical
- terrestrial
- Terrestrial Biomes
- desert or dune
- savanna or grassland
- chaparral
- forest
- rainforest
- scrub forest
- mountains
- Other Habitat Features
- urban
- suburban
- agricultural
Systematic and Taxonomic History
The first documented interaction between Europeans and marsupials occurred in 1500
AD when a
southern opossum
, now included in family
Didelphidae
, was presented to Spain's King Ferdinand and Queen Isabella by the explorer Vicente
Pinzon.
Didelphidae
is considered the basal marsupial family. The first metatherians were likely found
in North America and spread to South America before the separation of Australia, Antarctica
and South America in the tertiary period. The division between
didelphids
and other metatherians likely occurred between 62 and 69 million years ago. Fossil
records for order
Didelphimorphia
suggest that these animals have historically been found in Europe and Africa in the
Oligocene and Miocene, in Asia in the Oligocene, in North America from the Pleistocene
until present and in South America from the Cretaceous until present. Due to their
basal, ancestral relationship to other marsupials, the
didelphid
body plan is considered very primitive and generalized. Contemporary
didelphids
likely emerged from a small to medium sized scansorial animal, without limb specializations.
Physical Description
Family
Didelphidae
is an ancestral group, not surprisingly; these animals maintain many morphological
similarities to early mammals including a long rostrum, a well-developed sagittal
crest and short limbs.
Didelphids
range in size from 10 g in genus
Monodelphis
to over 2 kg in genus
Didelphis
. Including their tails, the smallest members may be 170 mm long, whereas the largest
members may be over 1,000 mm long. Sexual dimorphism is present in many
didelphid
species, with males larger than females. Their pelage varies between woolly or fine
and often includes guard hairs or underfur. Their fur is typically darkly colored,
but may vary to a pale gray or yellow-brown. Many species of
didelphids
also have a dark facial mask that encircles their eyes. All
didelphids
have the same dental formula: 5/4, 1/1, 3/3, 4/4, with a total of 50 teeth. These
animals have conical upper incisors, polyprotodont lower incisors and large canines.
In general, the larger members of the family have a pouch; smaller members may have
simple lateral folds on their abdomen instead. In either case, these animals may have
anywhere from 4 to 27 functional mammae. Their tails are often very long and prehensile
with very little hair; however, some members have short, non-prehensile, furry tails.
Some species are specialized with crassated tails that store fat for periods of torpor.
These animals have 5 digits on each foot, the hallux and pollex is opposable in many
species. The semi-aquatic
water opossum
is specialized with webbed hind feet. Many of these animals also have long sensitive
vibrissae.
- Other Physical Features
- endothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
Reproduction
Members of family
Didelphidae
are considered polygynous. Males from studied species compete for reproductive females.
In laboratory tests, male
didelphids
often follow, chase and circle females, while producing clicking noises. Generally,
didelphids
show neither courtship displays nor pair bonds.
- Mating System
- polygynous
Members of family
Didelphidae
become sexually mature between 6 and 10 months of age and produce 1 to 4 polytocous
litters per year.
Didelphids
are primarily seasonal breeders, although some species, such as
gray short-tailed opossums
, breed nearly year round. Their breeding season is largely dictated by food availability.
In the seasonal tropics, breeding typically coincides with the dry season, whereas
in less seasonal environments the breeding season may be longer. These animals have
a very short gestation period that often lasts no more than 2 weeks, after which,
several altricial young are born. Their tiny newborns are about 1 cm long and weigh
about 0.13 g. At birth, many of their organs and systems have not fully formed; however,
these animals have very precocial forelimbs with sharp deciduous claws that allow
them to climb from the cloaca to their mother’s mammae. Although these animals have
4 to 27 mammae, many species produce more offspring than they can nurse and a large
number of newborns perish. Larger species, such as members of the genera
Didelphis
,
Chironectes
,
Philander
and
Lutreolina
, typically have a pouch; smaller species have lateral abdominal folds located near
their mammae. Once the newborns are attached, they nurse constantly for several more
weeks, during this time they complete their development. Males of some species show
partial semelparity, after breeding, these males have high mortality rates and a low
body condition.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
Young
didelphids
are cared for solely by their mother, there are no reports of male parental investment.
While attached to the mammae, young are kept warm by their mother’s body heat. After
the attachment period, young remain associated with their mother for several more
weeks and continue nursing. During this time, it is common for offspring to ride on
their mother’s fur during nighttime excursions. Typically, young leave their mother’s
care during the wet season. Litters born late in the season tend to be smaller and
have higher mortality rates. Likewise, older females often have fewer offspring per
litter. Regardless of age, females with only one offspring may not be able to produce
milk due to the low level of stimulation.
- Parental Investment
- altricial
- female parental care
Lifespan/Longevity
In general,
didelphids
have a fairly short lifespan. In the wild, these animals typically live 1 to 3 years;
however, their infant mortality rate is also very high. In captivity, many
didelphids
survive up to 8 years.
Behavior
Members of family
Didelphidae
are nocturnal and are often crepuscular as well. Generally, these animals are solitary
but they may congregate while feeding, although they do not usually interact. In laboratory
tests, male
didelphids
were extremely aggressive with other male conspecifics and fought often. Males did
not show a similar level of aggression toward female conspecifics. These animals have
several modes of locomotion including terrestrial, scansorial, arboreal and semi-aquatic
(
water opossums
). Many species utilize nests by either creating them, using the nests of other species
or using tree hallows. Nesting substrates include dry leaves, roots and grasses. Some
species enter torpor due to low food availability and extreme temperatures.
- Key Behaviors
- arboreal
- scansorial
- terricolous
- nocturnal
- crepuscular
- motile
- hibernation
- daily torpor
- solitary
Communication and Perception
Members of family
Didelphidae
are not often noisy. When they do produce sound, it typically varies between four
distinct types, tonal chirps, growls, clicks/hisses or screams. These animals are
sensitive to high frequency sounds, but their sensitivity to general noises may be
low. Their hearing is somewhat limited compared to placental mammals and has to do
with their primitive inner ear morphology. The hearing range of studied species typically
was most acute at 8 to 64 kHz. Regardless,
didelphids
communicate vocally during breeding season and to maintain contact with their young.
Young
didelphids
may produce bird-like screams and adult females may produce clicking and lip smacking
sounds.
Didelphids
have fairly well-developed eyesight, as is evident from their ability to capture
prey and walk on narrow vines. As compared to other groups, such as primates, their
visual acuity is fairly poor, although some species are able to discriminate between
prey items at a distance of about 60 cm. Similar to other nocturnal species, the light
gathering ability of their eyes is extremely well developed. Although it is still
somewhat debated, current research suggests that these animals have dichromatic vision.
When they perceive danger, these animals may produce visual displays such as opening
their mouth and curling their lips. Olfaction is an extremely important mode of perception
among
didelphids
. These animals have scent glands, which are used during breeding season to attract
mates. In these situations, males scent mark more frequently than females using their
head, flank and chest. Sexually immature males do not show scent marking behaviors.
Likewise, olfaction is an important means of communication between mothers and their
offspring. After parturition, females often produce a musky secretion that stains
their fur and the fur of their offspring. This may help maintain contact if they are
separated. Likewise,
didelphids
use their vomeronasal organ in selecting their food.
Didelphids
with impaired vomeronasal organs show no preference when selecting food as opposed
to non-altered animals, which can be rather selective.
- Other Communication Modes
- scent marks
Food Habits
Overall,
didelphids
are opportunistic omnivores; these animals eat a broad range of invertebrates, vertebrates
and plant material. There is variation in the group regarding the degree of insectivory,
carnivory and frugivory, but almost all members consume at least a small amount of
each of these food items, although their diet generally changes based on food availability.
Species found in urban environments may feed on garbage produced by humans and food
intended for domestic pets. Many members of family
Didelphidae
are immune to the snake venom of family
Vipiridae
and may actively hunt rattlesnakes. Likewise, although
didelphids
are impacted by the chemical release produced by
harvestmen
spiders, many opossums still consume them.
- Primary Diet
- omnivore
Predation
Didelphid
opossums are prey items for many predators within their various habitats including
felids
,
canids
, birds of prey,
rattlesnakes
and
coatis
. Not surprisingly, young opossums are the most vulnerable to predation. These animals
may run or climb a tree to avoid a predator, when cornered,
didelphids
may attempt to bite their attacker. Some species may even enter a catatonic state
when they are exposed to extreme stress; colloquially known as ‘playing opossum’,
this response is relatively rare.
Ecosystem Roles
Many
didelphids
act as important seed dispersers due to their at least partially frugivorous diet.
These animals are also used as hosts for a variety of internal and external parasites
including
fleas
,
ticks
,
chiggers
and
mites
, as well as
cestodes
,
nematodes
and
acanthocephalan worms
.
- fleas ( Siphonaptera )
- ticks ( Ixodoidea )
- chiggers ( Trombiculidae )
- mites ( Acari )
- cestodes ( Cestoda )
- nematodes ( Nematoda )
- acanthocephalan worms ( Acanthocephala )
Economic Importance for Humans: Positive
Members of family
Didelphidae
may be used for human benefit in a variety of ways. Several species are hunted for
sport or food and their meat has been used in the wild game trade. Likewise, the pelts
of some species have been used for relatively low quality fur. In addition, several
opossum species are used as study organisms in scientific laboratories. A few species,
such as
Virginia opossums
and
gray short-tailed opossums
have been used in the pet trade. These pets are illegal in many areas of the United
States but are reportedly trainable. Historically, opossum fat, meat and bones have
been used to treat and prevent a variety of ailments such as stomach discomfort, inflammation,
labor pains, asthma, headaches, toothaches, ear aches, sore throat, allergies, epilepsy,
dermatitis, coughing and heart attacks.
- Positive Impacts
- food
- body parts are source of valuable material
- source of medicine or drug
Economic Importance for Humans: Negative
Didelphid
opossums may transmit parasites and human ailments such as Chagas disease and Leishmaniases.
Opossums living near human settlements also have a tendency to knock over trash cans
in an effort to feed on human refuse and may consume food left for domestic pets.
Large
didelphids
often raid poultry farms, killing chickens. Several of the more frugivorous species
may steal crops from orchards and pineapple plantations, however, the crop loss and
damage from
didelphids
is generally considered minimal. These animals may also disrupt scientific research
due to their propensity to kill animals captured in mist nets.
- Negative Impacts
-
injures humans
- carries human disease
- crop pest
- causes or carries domestic animal disease
Conservation Status
Members of family
Didelphidae
are under a variety of conservation risk levels according to the IUCN Red List of
Threatened Species. At least 2 species are currently considered critically endangered,
both
Handley's slender mouse opossums
and
one-striped opossums
, are endangered due to their small amount of viable habitat. At least 7 species are
currently considered vulnerable including
Karimis fat-tailed opossums
,
red three-striped opossums
,
Reigs opossums
,
junin slender opossums
,
Chacoan pygmy opossums
,
little woolly mouse opossums
and
dryland mouse opossums
, the immediate threats to these species include habitat conversion to agriculture,
logging and the encroachment of human settlements. At least 3 additional species are
currently near threatened including
wood sprite gracile mouse opossums
,
Handleys short-tailed opossums
and
Paraguayan fat-tailed mouse opossums
. Likewise, there is one species that is recorded as newly extinct,
red-bellied gracile mouse opossums
have not been seen since 1962, their entire recorded habitat has been converted to
agricultural land and used for human industry. The conservation status of several
other species has yet to be evaluated.
Additional Links
Contributors
Leila Siciliano Martina (author), Texas State University.
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- temperate
-
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- desert or dunes
-
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
- tropical savanna and grassland
-
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
- savanna
-
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
- temperate grassland
-
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
- chaparral
-
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- 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.
- scrub forest
-
scrub forests develop in areas that experience dry seasons.
- mountains
-
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
- urban
-
living in cities and large towns, landscapes dominated by human structures and activity.
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- agricultural
-
living in landscapes dominated by human agriculture.
- polygynous
-
having more than one female as a mate at one time
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- 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.
- female parental care
-
parental care is carried out by females
- arboreal
-
Referring to an animal that lives in trees; tree-climbing.
- nocturnal
-
active during the night
- crepuscular
-
active at dawn and dusk
- motile
-
having the capacity to move from one place to another.
- hibernation
-
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
- solitary
-
lives alone
- visual
-
uses sight to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- scent marks
-
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- food
-
A substance that provides both nutrients and energy to a living thing.
- drug
-
a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease
- causes or carries domestic animal disease
-
either directly causes, or indirectly transmits, a disease to a domestic animal
- omnivore
-
an animal that mainly eats all kinds of things, including plants and animals
- 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.
- 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.
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