Abstract. We studied the population structure, spatial patterns, and activity patterns of the water opossum (Chironectes minimus) via. Abstract. The male genital system was examined in 9 male specimens of Chironectes minimus (2 adult and 7 young) from Brazil. Unlike other. AnAge entry for Chironectes minimus. Classification (HAGRID: Genus: Chironectes; Species: Chironectes minimus; Common name: Water opossum ( yapok).
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We studied the population structure, spatial patterns, minmus 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. The longer home lengths for males may explain the observed sex ratio bias, because males are more exposed to capture. All individuals used stream stretches with preserved chironectws forest, fast-flowing water, and stony substrate.
The hypothesis that activity was homogeneously distributed throughout the night was rejected; activity began right after sunset and ended before sunrise, but with higher levels of activity in the first 6 h of the night.
Because of anthropogenic alterations of hydrographic basins, water opossums may be threatened by reduction of their main habitat, streams with fast-flowing water and stony substrate. The water opossum Chironectes minimus is the only semiaquatic marsupial Marshall ; Mondolfi and Padilla ; Nowak Water opossums have many cuironectes convergences with otters, plus several unique features Marshall ; Nowak Like otters, they have a streamlined body shape, large webbed hind feet, dense, nonwettable fur, and supernumerary facial bristles Marshall ; Nowak This last feature allows a female to swim with young in her pouch and protects a male’s scrotum from low water temperatures Marshall ; Nowak Water opossums occur in water bodies from southern Mexico to northern Argentina Nowak Despite their wide distribution, there is little and inconclusive information about their ecology Mondolfi and Padilla ; Zetek Most studies that mention the water opossum to date merely record its presence in faunistic surveys, with a few morphophysiological and genetic studies, and a few on its behavior in captivity Nowak Its abundance in nature is controversial.
In Peru Terborgh et al. Emmons and Feer regarded it as rare throughout its distribution. In most studies, captures or sightings occurred mainly in forested streams with clear, fast-flowing waters.
As for the breeding season, females with offspring were captured in January, July, and November in Venezuela Mondolfi and Padilla ; in Brazil, females with offspring were captured between December and Chirpnectes Nowak ; and in northern Argentina, the presence of offspring was recorded in August Monteiro-Filho et al.
Nothing is known, among other subjects, about population structure, reproduction in the wild, spatial patterns home lengths and overlaps and habitat selectionand activity patterns of water opossums. In all these aspects, there are open questions as to whether the patterns shown by water opossums are similar to those found in other neotropical marsupials, due to phylogenetic minimmus, or if they are similar to those shown by other semiaquatic mammals, indicating that ecology had a preponderant role minijus shaping these characteristics.
Because of their semiaquatic and nocturnal habits, water opossums have seldom been captured by the traditional methods used for other small mammal species Mondolfi and Padilla An efficient method for trapping the water opossum was only developed in Bressiani and Graipelenabling more thorough studies of their ecology.
The present study chjronectes on the ecology of water opossums in Atlantic Forest streams in southeastern Brazil, attempting to fill some of the many gaps in the knowledge of this species and to test some hypotheses chironextes its reproductive seasonality, spatial patterns, and activity patterns.
Regarding reproduction, we tested the hypothesis that water opossums show reproductive seasonality, as usual among neotropical marsupials Fleming ; Fonseca and Kierulff ; O’Connell ; Tyndale-Biscoe and Mackenzie Alternatively, minimsu by water opossums could reflect the absence of a well-defined seasonality in its river habitat. Regarding spatial patterns, we estimated the home lengths—the distance along the river course between the most widely separated locations of each individual—and analyzed home-length overlaps.
The alternative hypothesis in this case is that water opossums show different spatial patterns reflecting its peculiar habitat for a didelphid. We also described the activity pattern of water opossums to determine whether activity is homogeneously distributed throughout the night or if there are well-defined peaks of activity.
The region is greatly influenced by the surrounding mountain ranges, which reach elevations around 1, m above sea level Mantovani The vegetation of the region has been classified as submontane rain forest, and nowadays it includes secondary vegetation and original forest remnants Mantovani Location of study area in Brazil and in Rio de Janeiro State left ; middle course of minimud Aguas Claras River subbasin, with the studied rivers and tributaries right.
The black square indicates a dam in Aguas Claras River; the arrow indicates a waterfall sequence in Floresta River. Near the confluence with the Dona Rosa River, there is a 3-m-high inactive dam. It has well-preserved habitats along its entire course, with few areas without riparian forest, and consists of runs and riffles with stony substrate.
Along its course there is a sequence of 3 waterfalls up to 12 m high.
The Dona Rosa River is 2. Methods for trapping and handling animals met guidelines approved by the American Society of Mammalogists Gannon et al. Shown minius sampling period, extension of river sampled in mnumber of traps in each trapping session, and sampling effort in trap-nights throughout the study period. The Floresta River also was sampled in the period between July and Octoberwith 15 traps for each trapping session.
Water opossum (yapok) (Chironectes minimus) longevity, ageing, and life history
Each trapping session comprised 5 consecutive nights of livetrapping. We placed trap stations in favorable river sites, in order to maximize capture success see below. The distance between consecutive trap stations varied between 20 and m. Each trap station had 1—3 traps. According to this sampling design, we set 10— traps in different river stretches in each trapping session Table 1.
Following the method developed by Bressiani and Graipelwe placed double-door wire-mesh live traps We built barriers in suitable places in the rivers, using stones and branches, in a way to direct the water flow through the trap, inducing the animal to enter.
After each trap session, traps were removed and barriers undone. Up to Marchwe used no bait in the traps. From Aprilwe baited the traps with different types of bait. In April and May, the bait was bacon and fruits, and between June and October, the bait was shrimp Litopenaeus vannamei or fish Engraulidae.
To test the null hypothesis that trapping success was not affected by the use of bait, we performed a t -test. From January to Octoberexcept March and August, we placed 23 single-door wire-mesh live traps Between January and June, we baited the traps with a mixture of peanut butter, banana, oats, and bacon.
In the following months, the bait used was the same used in the double-door traps set in the other rivers. Animals captured were individually marked using numbered ear tags model ; National Band and Tag Co.
For each individual captured, we recorded trap station, sex, reproductive condition pouch young and swollen mammae for females, and testes position for malesbody measurements weight and tail lengthand age by tooth-eruption sequence. Because the tooth-eruption pattern for C. This classification divides the individuals into juveniles with deciduous premolarssubadults definitive premolars and 3 molarsand adults definitive premolars and 4 molars.
After recording data, we released each individual at the point of capture. We used a chi-square test with Yates correction to test the null hypothesis that sex ratio was 1: To analyze the reproductive seasonality of water opossums, we 1st used a Spearman correlation to verify if the number of juveniles captured was correlated with the number of nonjuveniles captured, to test the hypothesis that temporal variation in the number of juveniles captured merely reflected the variation in sample sizes.
Then we used circular statistics to test the null hypothesis that recruitment was randomly distributed throughout the year, by applying Rayleigh’s test program ORIANA 2. All statistics followed Zar Radiotagging and tracking methods. There were no obvious adverse effects of the radiocollars on the animals. This technique consists of following the transmitter signal until visual contact with the animal tracked is achieved White and Garrott A location also was recorded cironectes it was possible to hear the radiosignal with the antenna disconnected from the receiver, following Lira et al.
To prevent autocorrelated locations of the same individual, we obtained locations at intervals of at least 1 h Endries and Adler ; Linders et al. Although many techniques are available to analyze how an individual uses the landscape Harris et al. Therefore, we estimated home length of each individual as the distance in meters along the river course between the most widely separated locations of that individual van der Ree and Bennett We used locations obtained both through radiotelemetry and trapping to estimate chironectds lengths.
We assessed static home-length overlaps for individuals that were tracked simultaneously Dunn and Gipson ; Powell ; White and Garrott Overlaps were estimated by the proportion of the home length of individual A overlapped by that of individual B, and by the proportion of the home length of individual B overlapped by that of individual A van der Ree and Bennett We obtained occasional diurnal fixes to check for possible diurnal activity.
We detected activity as fluctuations in the transmitter’s signal strength. For each individual, we grouped the number of active locations, beginning at the sunset, in 4 periods of 3 h. To test the null hypothesis that both sexes had the same activity pattern, we used the G -test. To test the null hypothesis that water chirlnectes showed uniform activity over the night we also used the G miniums, for both sexes separately.
With a trapping effort of 3, trap-nights, we obtained 47 captures chirpnectes 21 individuals of C. Captures were concentrated in 3 streams: In each of the tributaries Tf 1 and Tf 2 there was a single capture of a water opossum, and chironectse tributaries Ta 1 and Ta 3 there were no captures.
Between January and Maythere were no captures of water opossums. However, in the same period of the following year, we obtained 8 captures. During the 1st months ofstrong rains occurred that must have affected trappability. When bait was offered to trapped water opossums, they accepted only shrimp and fish. The first 2 species were captured both in traps within the river and at the margin; the latter 2 were captured only in traps at the margin.
However, the variation in density did not chironectws a seasonal pattern Fig. Throughout the study, the sex ratio was strongly biased toward males. Out of 47 captures, 38 were of 18 males and 9 were of 3 females individuals: Adult weights did not differ between sexes weights: The residence time time between the 1st and last capture for individuals captured in at least 2 trapping sessions ranged between 28 and days.
The line represents the density, in number of individuals per chironectss of river. White and gray bars represent the numbers of juveniles and females captured, respectively. The arrow indicates the only female that was not reproductive. The only 2 reproductive females were captured in August, September, and October Fig.