We studied the population structure, spatial patterns, and activity patterns of the water opossum Chironectes minimus via capture—mark—recapture and radiotelemetry from October to October in Atlantic Forest streams in southeastern Brazil. We tested the hypothesis of reproductive seasonality, the usual pattern in neotropical marsupials, by examining recruitment of juveniles. The hypothesis was rejected, supporting the alternative hypothesis that breeding by water opossums was better explained by its habitat characteristics and prey availability than by its phylogenetic ancestry. The observed sex ratio was significantly biased toward males. The home lengths of individual water opossums varied from to 3, m. Males had larger home lengths than females, and there were male—male and male—female overlaps.

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Chironectes minimus water opossum or yapok is native to tropical and subtropical habitats from southern Mexico to Central and South America. 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.

Finally, the geographic distribution of C. Water opossums are most often found in semi-aquatic or aquatic habitats, particularly in freshwater streams and near-shore lakes associated with tropical or subtropical forests. Their preferred habitat ranges from 0 to 1, m above sea level.

Dens are constructed just above the 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 are used as resting spots; these nests are located on the ground and are 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.

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 length of 35 cm. These animals weigh between to g and average g.

They are sexually dimorphic, with males 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, their tail is used as a rudder while swimming.

Their tail may also be used for carrying or manipulating objects. Another distinguishing feature is the 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 them in maneuvering through water, 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 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 the soles and palms of both hind- and forefeet are minimal; this has been attributed to their 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 their 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. Chironectes minimus is polygynandrous. Females are polyestrous and breed up to 2 to 3 times per breeding season. This species shows pre-copulatory 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, ; Marshall, ; Nowak and Wilson, Like most mammals, Chironectes minimus is viviparous, with internal fertilization. Their 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 their 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.

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.

This usually occurs around day 40, almost immediately after their eyes begin to open. Juvenile 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 parental investment in young. Galliez, et al. There is no information available regarding the average lifespan of water opossums in the wild. However, gray four-eyed opossums , a close relative of water 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, ; Marshall, ; Nowak and Wilson, 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. Common familial groups consist of one female, one male and their offspring, larger groups are uncommon. The length of time young remain with their mother before becoming completely independent is not known. In captivity, C. It is an excellent swimmer and diver.

Although predominantly terrestrial, C. 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, ; Marshall, ; Nowak and Wilson, ; Salazar, et al. Although the average home range size of Chironectes minimus is unknown, home length, the distance along the river between conspecific dens, ranges between to 3, m. The home length of males is about 4 times larger than that of females, resulting in greater overlap of male habitats. 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 the water. Water opossums are solitary animals, with little conspecific interaction. During mating season, however, both sexes use pheromones to attract potential mates. 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 consist primarily of crustaceans , but also includes aquatic insects and frogs. It also consumes oil producing prey that helps maintain its waterproof coat.

In addition, C. 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. There is little information available regarding predators specific to Chironectes minimus. Tortato 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 are relatively rare within this habitat and likely have little impact on the overall population. Wild cats, such as ocelots , jaguars , pumas and jaguarundis likely prey on C. Its nocturnal lifestyle and burrowing tendencies likely help reduce its risk of predation.

Fleck, ; Marshall, ; Marshall, ; Smith, ; Tortato, 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 nests that are used by other water opossums once they are abandoned.

There is no information available regarding parasites specific to this species.


Water opossum

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 believed to be 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. 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, 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.

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