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. (Cuarón, et al., 2010; Marshall, 1978)
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. (Cuarón, et al., 2010; Elliot, 1904; Marshall, 1977; Marshall, 1978; Zetek, 1930)
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. (Cuarón, et al., 2010; Elliot, 1904; Hume, 1982; Marshall, 1977; Marshall, 1978; McLean, 1993; Nowak and Wilson, 1999)
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. (Cuarón, et al., 2010; Elliot, 1904; Hume, 1982; Marshall, 1977; Marshall, 1978; McLean, 1993; Nowak and Wilson, 1999)
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. (Cuarón, et al., 2010; Elliot, 1904; Hume, 1982; Marshall, 1977; Marshall, 1978; McLean, 1993; Nowak and Wilson, 1999)
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. (Marshall, 1977; Marshall, 1978; Nowak and Wilson, 1999)
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. (Cuarón, et al., 2010; Galliez, et al., 2009; Marshall, 1977; Marshall, 1978; Nowak and Wilson, 1999)
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. (Galliez, et al., 2009; Julien-Laferriere and Atramentowicz, 1990; Marshall, 1978)
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. (Hume, 1982; Marshall, 1978; Nowak and Wilson, 1999)
Like many marsupials, Chironectes minimus is primarily nocturnal. However, it is commonly observed foraging or performing other activities during the day. Individuals are typically non-social and solitary. Although familial groups consisting of one female, one male and their offspring are not uncommon, groups larger than this are. It is not known how long young remain with their mothers before becoming completely independent. In captivity, C. minimus is reportedly aggressive when handled. It is an excellent swimmer and diver. Although predominantly terrestrial, C. minimus is well-adapted to a semi-aquatic lifestyle. Unlike most opossum species, its tail is critical to its exceptional swimming ability. It also has been observed using its thick, prehensile tail to gather and collect objects. (Marshall, 1977; Marshall, 1978; Nowak and Wilson, 1999; Salazar, et al., 1994)
Although the average home range size of Chironectes minimus is unknown, home length, the distance along the river between conspecific dens, ranges between 844 to 3,388 m. The home length of males is about 4 times larger than those of females, resulting in greater overlap of male habitats when compared to those of females. (Galliez, et al., 2009; Marshall, 1978; Nowak and Wilson, 1999)
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. (Galliez, et al., 2009; Marshall, 1977; Marshall, 1978; Nowak and Wilson, 1999)
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. (Elliot, 1904; Marshall, 1977; Marshall, 1978; McLean, 1993; Nowak and Wilson, 1999)
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. (Fleck, 1995; Marshall, 1977; Marshall, 1978; Smith, 2007; Tortato, 2009)
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. (Marshall, 1977; Marshall, 1978)
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. (Cuarón, et al., 2010; Marshall, 1977; Marshall, 1978; Nowak and Wilson, 1999)
There are no known adverse effects of Chironectes minimus on humans.
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. (Cuarón, et al., 2010; Nowak, 1999)
Taylor McHugh (author), Radford University, Christine Small (author, editor), Radford University, John Berini (editor), Special Projects.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
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.
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.
an animal that mainly eats meat
uses smells or other chemicals to communicate
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.
parental care is carried out by females
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
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).
seaweed. Algae that are large and photosynthetic.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
an animal that mainly eats all kinds of things, including plants and animals
chemicals released into air or water that are detected by and responded to by other animals of the same species
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
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