Water opossums are nocturnal and semi-aquatic and use tactile, auditory, and olfactory senses for foraging and reproduction. Their sensitive ears and whiskers are important in detecting prey in the dark and in water. Water opossums are solitary animals, with little intraspecific interaction among conspecifics. During mating season, however, both sexes use pheromones to attract potential mates.
Communication Channels: chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; acoustic ; chemical
Although populations of Chironectes minimus are currently in decline, the IUCN Red List of Threatened Species classifies it as a species of least concern. This species is widely distributed and locally abundant. Currently, there are no major threats to the long-term survival of this species. However, potential threats include deforestation, water pollution or contamination, and habitat deterioration, particularly in freshwater ecosystems. Declines of freshwater invertebrate prey due to deforestation and pollution could also be a point of concern in the near future. It is uncertain whether this species is rare, or if it is infrequently encountered due to its nocturnal lifestyle and use of relatively inaccessible habitats.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
There are no known adverse effects of Chironectes minimus on humans.
Chironectes minimus is hunted by humans for its waterproof fur. Although its skin has little value in most countries, there is an increasing demand in parts of Peru.
Positive Impacts: body parts are source of valuable material
Chironectes minimus is an important predator of aquatic prey, including aquatic insects and insect larvae. As a result, this species may help control insect pest populations throughout their geographic range. They also create dens and nest that are used by other water opossums once they are abandoned. There is no information available regarding parasites specific to this species.
Ecosystem Impact: creates habitat
Chironectes minimus is carnivorous, typically foraging near fresh water streams, lakes, and rivers to feed on a variety of aquatic organisms. It has also been observed at high elevations trailing rivers along mountains. Prey consists primarily of crustaceans, but also includes aquatic insects and frogs. It also consumes oil producing prey that help maintain its waterproof coat. In addition, C. minimus has been observed feeding on fruits and various aquatic plants when other food sources are limited. Chironectes minimus often displays aggressive behaviors when feeding, and tends to consume large quantities of food. In terrestrial habitats, it sits on its hind legs, rapidly and aggressive tearing food with its sharp teeth. Similar to sea otters, C. minimus secures hard-bodied crustacean prey on its abdomen and cracks open the hard exoskeleton.
Animal Foods: amphibians; fish; insects; aquatic crustaceans
Plant Foods: leaves; fruit; macroalgae
Primary Diet: carnivore (Eats non-insect arthropods); omnivore
Chironectes minimus (water opossum or yapok) is native to tropical and subtropical habitats from southern Mexico to Central and South America. It is most common in northern South America, with documented occurrences in Colombia, Ecuador, Peru, Venezuela (rare), Guyana, Suriname, and French Guiana. This species also has been reported in southeastern Brazil, Paraguay, and northeastern Argentina. There are 4 recognized subspecies of Chironectes minimus, each with a relatively distinct geographic range. Chironectes minimus argyrodtes has the northern-most distribution and is found almost exclusively in southern Mexico (just north of Oaxaca), El Salvador and Honduras. The geographic range of C. m. panamensis extends from southern Central America through northwestern coastal countries in South America. Chironectes minimus minimus can be found primarily in northern South America, throughout Venezuela, Columbia and Guiana. Finally, the geographic distribution of C. m. bresslaui includes southern Brazil, Paraguay, and northeastern Argentina.
Biogeographic Regions: neotropical (Native )
Water possums are found most often in semi-aquatic or aquatic habitats, particularly in freshwater streams and near-shore lakes associated with tropical or subtropical forests. Preferred habitat ranges from 0 to 1860 m above sea level. They have relatively elaborate dens that descend into the ground at a 45 degree angle from the entrance, tunneling about 0.6 m in length until reaching a nest area. Dens are constructed just above water level within stream banks and are found in moderately dense cover and cleared tropical forest areas, often between tree roots or in small holes adjacent to water. Burrows are relatively large, and can sustain low levels of water. Diurnal nests are sometimes built near dens in areas of low light, and used as resting spots; these nests are located on the ground composed of gathered grasses and leaves. Water opossums avoid defecating in or near their nesting site, possibly to deter predation since they reside next to commonly visited water sources.
Range elevation: sea level to 1,860 m.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: forest ; mountains
Other Habitat Features: riparian
There is no information available regarding the average lifespan of water opossums in the wild. However, gray four-eyed opossums have a mean lifespan of 2 years in the wild. In captivity, water opossums have been reported to live 1 to 3 years. The oldest known specimen lived for 2 years and 11 months.
Range lifespan
Status: captivity: 3 (high) years.
Typical lifespan
Status: captivity: 1 to 3 hours.
Water opossums are small, rodent-like marsupials with short grayish-white and brown fur. They range in size from 27 to 40 cm long, with an average of 35 cm, and from 604 to 790 g in weight, with an an average of 697 g. They are sexually dimorphic, with males being larger than females. Their long skinny tails are nearly as long as or longer than their bodies and range in length from 30 to 43 cm. Unlike other opossums, water opossums do not use their tails to climb. Instead, the tail is used as a rudder while swimming. The tail may also be used for carrying or manipulating objects. Other distinguishing features include a unique white stripe above their eyes and beneath their lower jaw. Facial bristles and whiskers under each eye serve as important sensory organs. These tactile hairs aid water opossums in maneuvering through water and sensing nearby predators and potential prey. Their appearance has been described as most similar to gray four-eyed opossums, another member of family Didelphidae.
Water opossums are the only extant aquatic marsupial and are well-adapted to their aquatic habitat. Their streamline body is covered with a water-repellent coat that enhances buoyancy. This allows them to float on the surface of the water and to swim rapidly and efficiently. Virginia opossums, a closely related terrestrial species, are strong but slow swimmers. Lacking the water-repellent coat of water opossums, Virginia opossums must expend greater amounts of energy to keep their body afloat. Water opossums also have broad, webbed hindfeet, which they use to move through the water. THeir forefeet, in contrast, are not webbed but consist of long, naked fingers for catching prey. Padding on soles and palms of both hind- and forefeet are minimal; this has been attributed to its aquatic or soft-substrate habitats, particularly muddy banks of river and streams.
Another aquatic adaptation of water opossums is the presence of a water-proof pouch or sphincter known as the pars pudenda. This organ is essential for the survival of offspring, who remain in the mother's pouch during underwater dives. The pars pudenda creates a water-free environment for young that are not yet weaned. Males also possess this sphincter; however, it does not completely cut off the flow of water through the pouch. Rather, it appears to function only to protect the male genitalia while underwater.
Range mass: 604 to 790 g.
Range length: 30 to 40 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Average basal metabolic rate: 2.793 W.
There is little information available regarding predators specific to Chironectes minimus. Tortato (2009) reported a single predation event by a roadside hawk in Brazil. Chironectes minimus also has been reported in the diet of large eagles such as hawk-eagles, however, these birds relatively rare within C. minimus habitat and likely have little impact on overall population. Wild cats such as ocelots, jaguars, pumas and jaguarundis likely prey on C. minimus as well. Its nocturnal lifestyle and borrowing tendencies likely help reduce risk of predation.
Known Predators:
Chironectes minimus is polygynandrous and females are polyestrous, as reproductive females can reproduce more than once in a single breeding season. Females breed up to 2 to 3 times per breeding season. The species as a whole shows precopulatory behaviors, with males and females developing strong social bonds. When mating occurs, males pull females close prior to mounting. When females are carrying offspring, males often circle them as a means of defense.
Mating System: polygynandrous (promiscuous)
Like most mammals, Chironectes minimus is viviparous, with internal fertilization. Breeding season varies geographically. In Brazil, breeding occurs from December through February. In Venezuela, breeding occurs during January, November and July, and in Argentina, breeding occurs during the month of August. An average litter consists of 3 to 4 offspring. Immediately after parturition, neonates climb to the mother's pouch, where they begin nursing. Within the first 38 days offspring develop fur, pigmentation, and their eyes begin to open. By the time young open their eyes, they are too large to remain in the mother's pouch but continue to nurse. Offspring become independent between 45 and 60 days after birth, but maintain a close social bond with their mother.
Breeding interval: Chironectes minimus exhibits polyestrus and can breed soon after giving birth.
Breeding season: Breeding season in Chironectes minimus varies geographically but typically occurs during spring and summer.
Range number of offspring: 1 to 5.
Average number of offspring: 3-4.
Range time to independence: 45 to 60 days.
Average time to independence: 53 days.
Average age at sexual or reproductive maturity (female): 304 days or 10 months.
Average age at sexual or reproductive maturity (male): 10 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Average number of offspring: 4.
Average age at sexual or reproductive maturity (female)
Sex: female: 304 days.
There is little information available concerning parental care in water opossums. However, they are likely similar to other members of Didelphidae in producing altricial offspring that remain attached to the mother's mammae. In related species, young remain in the mother’s marsupium, where the mammae are located, until they become too large. This usually occurs around day 40, almost immediately after their eyes begin to open. Although young can no longer remain in their mother’s pouch, they continue to nurse as they lack maure teeth for capturing prey. Developing water opossums develop strong social bonds with their mother and young tend to nestle with the female while sleeping and sometimes climb on their mother's back for transportation. There is no information available regarding paternal care. In gray four-eyed opossums, a closely related species, females leave young unattended for up to two weeks as they forage for food, suggesting little to no paternal investment in young.
Parental Investment: altricial ; female parental care ; pre-hatching/birth (Provisioning: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Male)
The water opossum (Chironectes minimus), also locally known as the yapok (/ˈjæpɒk/), is a marsupial of the family Didelphidae.[2] It is the only living member of its genus, Chironectes.[3] This semiaquatic creature is found in and near freshwater streams and lakes from Mexico through Central and South America to Argentina and is the most aquatic living marsupial (the lutrine opossum also has semiaquatic habits). It is also the only living marsupial in which both sexes have a pouch. The thylacine, commonly referred to as the Tasmanian tiger, also exhibited this trait, but it is now extinct.[4]
The water opossum lives in bankside burrows, emerging after dusk to swim and search for fish, crustaceans and other aquatic animals, which it eats on the bank.
The local name for the water opossum, "yapok", probably comes from the name of the Oyapok River in French Guiana.
The water opossum is a small opossum, 27–32.5 cm (10.6–12.8 in) long, with a 36–40 cm (14–16 in) long tail. The fur is in a marbled grey and black pattern, while the muzzle, eyestripe, and crown are all black. A light band runs across the forehead anterior to the ears, which are rounded and naked. There are sensory facial bristles in tufts above each eye, as well as whiskers. The water opossum's tail, furred and black at the base, is yellow or white at its end. The hindfeet of the water opossum are webbed, while the forefeet ("hands") are not. The forefeet can be used to feel for and grab prey as the animal swims, propelled by its tail and webbed back feet.[5] Unlike other didelphids, the water opossum does not have a cloaca.[6]
The water opossum has several adaptations for its watery lifestyle. It has short, dense fur, which is water-repellent. The broad hindfeet are webbed and are used for propulsion through water, moving with alternate strokes. They are symmetrical as well, which distributes force equally along both borders of the webbing; this increases the efficiency of the water opossum's movement through the water. The water opossum's long tail also aids in swimming.
Being a marsupial and at the same time an aquatic animal, the water opossum has evolved a way to protect its young while swimming. A strong ring of muscle makes the pouch (which opens to the rear) watertight, so the young remain dry, even when the mother is totally immersed in water.[5] The male also has a pouch (although not as watertight as the female's), where he places his genitalia before swimming.[6] This is thought to prevent them from becoming entangled in aquatic vegetation and is probably helpful in streamlining the animal as well.
Water opossums mate in December and a litter of 1–5 young is born 12 to 14 days later in the nest. By 22 days the offspring are beginning to show some fur, and by 40 days or so their eyes are open, their bodies protruding from the mother's pouch. At 48 days of age, the young opossums detach from the nipples, but they still nurse and sleep with the mother.
The water opossum seems to have a history dating as far back as to the Pliocene Epoch. The first Pliocene occurrences were recorded in 1902, 1906, and 1917 when two fragments of left mandibular ramus with alveoli (characterized as MACN 2464 and MACN 3515), as well as the fragment of the distal end of a humerus (MACN 3675) were collected near the city of Parani, Entre Rios Province, Argentina. The mandibular fossils, MACN 2464 and 3515 were known to be from the water opossum because their teeth were nearly indistinguishable from living populations of the organism in present day. Additionally, water opossum teeth are characteristically different from other didelphids, likely because they are the only semi-aquatic marsupials, making these teeth easy to identify.[7]
Holocene subfossil fragments of Chironectes have been discovered in São Paulo, Brazil. Also, there are fossil specimens from the late Pleistocene-Recent cave deposits in Minas Gerais, Brazil, as well as from the late Pliocene in Entre Ríos Province, Argentina.
The water opossum (Chironectes minimus), also locally known as the yapok (/ˈjæpɒk/), is a marsupial of the family Didelphidae. It is the only living member of its genus, Chironectes. This semiaquatic creature is found in and near freshwater streams and lakes from Mexico through Central and South America to Argentina and is the most aquatic living marsupial (the lutrine opossum also has semiaquatic habits). It is also the only living marsupial in which both sexes have a pouch. The thylacine, commonly referred to as the Tasmanian tiger, also exhibited this trait, but it is now extinct.
The water opossum lives in bankside burrows, emerging after dusk to swim and search for fish, crustaceans and other aquatic animals, which it eats on the bank.
