The duration of lactation in feral coypus (Myocastor coypus)

The frequency of consecutive reproductive stages in a post mortem sample of 423 lactating coypus was used to estimate the mean post partum interval (D_pp) and the mean duration of lactation ( D ₁). The estimates required a number of assumptions but the most important involved the validity of making time specific inferences from an "age" series. Variation statistics could not be calculated using conventional techniques and the jacknife method of estimation was used to obtain variances of the means and 95 % confidence intervals. D_pp was estimated as 21 ± 0–8 weeks. Some observations of retrapped wild animals showed that some animals conceived at an oestrus which occurred within a day or two of parturition. D _l was estimated in four different ways, three of which were quite closely related: these averaged 8–4 ± 10 weeks. But the fourth estimate, which is equally valid, was 70 weeks. A weighted average of the four estimates was 7–7 weeks with 95 % confidence limits of c . ± 10. The average suckling period of five captive females was 10–9 weeks. The most likely interpretation of the 42 % difference between this value and the estimate for wild females is attenuation as a result of a reduced nutrient intake in the feral population. D _L is substantially longer than predicted from an expression relating maternal weight to D _L in other mammals. This may be part of a maternal care strategy that centres on protection of space, and possibly of a food supply for milk production, rather than on defence of the young.     

The twenty-four hour activity cycle of captive coypus (Myocastor coypus)

The twenty-four hour activity cycle of captive coypus was investigated by direct visual observation, automatic recording and by measuring the amount of faeces eliminated at hourly intervals. Coypus were active from just before sunset and the "Zeitgeber" or cue for activity onset may be declining light. The activity period usually ended before sunrise and the interval between the end of the period and dawn was inversely related to temperature. The animals fed and defaecated throughout the active period and 80–86 % of the faecal pellets were produced in water. Refection started shortly after the end of the feeding period, when the animals had returned to the nest, and continued until an hour or two after midday.
A model is suggested which involves two passages of food through the gut and a cycle length of 24 hours from ingestion to defaecation. The feeding and defaecation periods were equal in duration, but the refection period was 40% shorter. Hypothetically this may be due to a caecum by-pass mechanism during the second passage of food through the gut so that the defaecation period, like the feeding period, is controlled by the rate at which food passes through the pyloric sphincter. In contrast the period of refection may be controlled by the rate at which food remains are voided from the caecum. Coypus spent the pre-dawn and daylight hours on nests and in contact with familiar conspecifics. These behaviours may have the function of temperature maintenance in the coldest part of the night and of avoiding diurnal predators.     

Scent marking and resource defence by male coypus (Myocastor coypus)

The alternative ideas that scent marking functions mainly in intrasexual competition or for attracting or stimulating mates were tested using data from a 16-year study of coypus, Myocastor coypus . Male coypus have a large anal gland, specialized for marking. Despite year-round breeding, the anal gland shows regular seasonal variation with marked enlargement in OctobeDecember. The analysis supported the hypothesis that this seasonal increase in glandular activity was linked to intrasexual competition: the size of the autumn peak was correlated with the increase in male numbers from the previous season and with the frequency of fighting scars. There were no relationships between gland size and any measures of the availability of mates. Increased scent marking may have been part of the response by resource-holding males to male recruits as these competed for existing territories. The timing of the autumn peak in marking and fighting may have been a response to the accumulation of non-resource-holding males over the summer (when recruitment exceeded mortality in the population) and to increasing accessibility within previously dense wetland habitats; together, these factors may cause a switch from scramble to despotic competition and an increase in scent marking to help keep the costs of resource defence within economic limits.     

Dermatophytes and other keratinophilic fungi from coypus (Myocastor coypus) and brown rats (Rattus norvegicus)

The occurrence of mycotic agents was investigated by hair-brush technique on the coat of 162 naturalized coypus (Myocastor coypus) and 64 indigenous brown rats (Rattus norvegicus) originating from the same protected area in Central Italy. The isolates from positive coypus (29.6%) were identified as Microsporum gypseum (14.8%), Trichophyton terrestre (9.8%), Alternaria sp. (3.7%), Trichophyton mentagrophytes (2.5%), Cladosporium sp. (1.8%), Scopulariopsis sp. (1.2%), and Chrysosporium keratinophilum (0.6%), whereas the isolates from positive rats (46.7%) were identified as M. gypseum (28.1%), T. mentagrophytes (12.5%), Chrysosporium tropicum and T. terrestre (3.1% each), and Chrysosporium inops (1.6%). Statistically, brown rats were more likely to harbor fungal agents (P < 0.05) on their coat than coypus, especially T. mentagrophytes (P < 0.01) and M. gypseum (P < 0.05). No positive animal showed dermatological lesions. The present results are the first providing basic information on the coat’s mycoflora of a wild coypu population. It is concluded that the coypu, an allochthonous rodent in Italy, can play a role as natural animal reservoir of dermatophytes and as carrier of keratinophilic and saprophytic fungi within its new habitat, though to a lesser extent than indigenous rats. Therefore, people who are exposed to the risk of contact with the coat of rats and coypus should take all the cautions needed to protect themselves from mycotic agents potentially transmissible to humans.     

A mortality survey of free range nutria (Myocastor coypus)

A review of the literature revealed little information on natural occurring diseases in wild nutria. In this report, a summary of necropsies performed on free-range animals from four different geographical areas, is presented. Fifty-two percent of the nutria had trauma (mostly by predation and road kill), 15% had poisoning by different toxics, and 11% had starvation. The rest died due to infectious diseases and miscellaneous causes, while 21 individuals had no significant lesions. The occurrence of infections seems sporadic with a far lower prevalence than in the farmed animals, while the incidence of poisoning is rather high. In addition, anthrax was diagnosed in two individuals. Thus, nutria are probably subject to mortality from a number of different human-induced causes rather than natural ones. Analysis of these records may provide insight into prevention of problem and better management practices.     

Modeling the spread of invasive nutrias (Myocastor coypus) over Iran

Nutria (Myocastor coypus) is a native aquatic rodent to South America, and was introduced to Europe, Asia, Africa and North America for fur farming. The South American nutria or coypu is now considered a pest in the area of introduction, because of its negative impact on biological diversity and ecological relationships. Having information on the invasion range of exotic species is crucial for understanding the ecology of invasive spread and for making good conservation and management planning to address this problem. At the beginning of the 20th century, nutria was introduced into Asia. Nutria was recorded for the first time in Iran in 1995. In the present study we proposed a multiple spatial scale approach to predict the invasion trends of the nutria in Iran, and to define up the “suitable scale” for predicting the invasion trends of this species. Our results highlighted the importance of environmental variables including vegetation density (for food and nesting) and water resource (streams, rivers, and lakes) in distribution of the nutria. Potential areas for the presence of the nutria are located near the Caspian Sea, west and central Iran which receive more precipitation than other parts of the country. Therefore, these parts of Iran may face a much greater risk of invasion risk in the future. Moreover, these results can show the possible risk of nutria invasion to the northern and western neighbors of Iran.     

Feeding strategy of coypu (Myocastor coypus) in central western France

The diet of coypu ( Myocastor coypus ) on two sites in a managed marsh was investigated by field observations and microscopic analysis of faeces. The habitat is mainly grazing pasture and over 51% of the plant fragments recovered from faeces were leaves of Graminaceae. Other food included hydrophytes, Cyperaceae, dicotyledons, flowers and seeds of Graminaceae and various roots. The mean annual diet of coypu was similar at both sites and showed moderate interannual variations. Relative proportions of different foods varied with season and availability. Hydrophytes, mostly Lemnaceae, were preferentially selected in late summer and autumn. Coypu fed on roots during winter, particularly in periods of exceptional food shortage due to flooding and severe frost. Even when crops were available, coypu utilized a wide range of food. The study shows the importance of feeding strategy in the ability of coypu to colonize new habitats, particularly those which are man-made.     

Climatic determinants of spring littering by feral coypus, Myocastor coypus

The fat reserves of adult female coypus in winter and the proportion of females littering in the following spring were measured between 1971 and 1979. Data were from post mortem material obtained during the current trapping programme in East Anglia.     

Seroprevalence for selected pathogens of zoonotic importance in wild nutria (Myocastor coypus)

Little information is present in the literature on diseases of the nutria (Myocastor coypus) in the wild. Serum samples obtained from 176 trapped animals were tested for antibody reactivity against 11 pathogens of significant zoonoses. Sera were positive against Leptospira (38.0 %, odds relative risk?=?0.03, Taylor series 95 % confidence limits 0.01–0.06), Toxoplasma gondii (27.8 %, odds relative risk?=?2.30, Taylor series 95 % confidence limits 1.23–4.31), Chlamydophila psittaci (21.0 % odds relative risk?=?4.94, Taylor series 95 % confidence limits 2.75–8.89), Streptococcus equi subspecies zooepidemicus (15.9 % odds relative risk?=?1.87, Taylor series 95 % confidence limits 1.04–3.37), and encephalomyocarditis virus (3.4 %, odds relative risk?=?0.05, Taylor series 95 % confidence limits 0.02–0.12). Some of the rodents showed antibodies at high titers, mostly indicating recent exposure. Seroprevalence rates varied among the location and age groups, although not by season or gender. All samples were seronegative for Brucella spp., Francisella tularensis, vesicular stomatitis virus, rabies virus, foot-and-mouth disease virus, and Encephalitozoon cuniculi.     

Giardia in beaver (Castor canadensis) and nutria (Myocastor coypus) from east Texas

We examined the prevalence of Giardia sp. infection in nuisance beaver (Castor canadensis) and nutria (Myocastor coypus) in east Texas. From October 1992 through September 1993, 100 beaver and 30 nutria were collected in routine wildlife management activities conducted by the U.S. Department of Agriculture-Animal and Plant Health Inspection Service-Texas Animal Damage Control Service. Fecal and duodenal mucoid samples were preserved from each animal. Fecal samples were examined for the occurrence of Giardia sp. cysts using the Merifluor immunoassay detection kit: 30 beaver (30.0%) and 20 nutria (66.7%) were positive for Giardia sp. Duodenal mucoid samples were examined for Giardia sp. trophozoites using trichrome staining. with 26 beaver (26.0%) and 20 nutria (73.3%) testing positive. Combining both techniques resulted in 33 beaver (33.0%) and 22 nutria (73.3%) testing positive for Giardia sp. We found no relationship between Giardia sp. and host age, sex, river system, habitat, county, or season in beaver. However, a relationship was found when season and habitat were considered together. No relationship was found between Giardia sp. and age, river system, habitat, county, or season in nutria: however, more males (87.5%) were infected than females (46.4%).     

海狸腺的组织学研究

该文通过对４０只成年雄性海狸鼠的海狸腺体,利用石蜡包埋切片法,并分别进行苏木素伊红染色法和过碘酸Ｓｃｈｉｆ氏组织化学染色法。在光学显微镜（ＮｉｋｏｎＪａｐａｎＯＰＴＩＰＨＯＴ２）×３２０、×６４０、×１６００下进行系统观察。结果发现,海狸腺属于皮脂腺,腺细胞为全浆分泌方式,且有一套完整的导管系统;利用过碘酸Ｓｃｈｉｆ氏组织化学方法,对其有效成分,糖蛋白和粘蛋白进行定性、定位。此物质存在于腺细胞的胞质内,尤其是接近成熟的腺细胞。     

Facultative variation in the timing of parturition by female coypus (Myocastor coypus), and the cost of delay

Female coypus Myocastor coypus in captivity produce more litters than expected by chance following days when they are undisturbed and less after they are disturbed. The observed distribution can be explained using simulations which assume that females can delay parturition for up to three days, depending on the level of disturbance on a previous day. The advantage of delay for wild coypus may be that parturient females can delay parturition if detected by a predator and move to a safer location. The main cost of delay is an increase in the average proportion of young that die in the last few days of pregnancy and in the days following parturition. These costs and benefits may be similar to those involved in the evolution of gestation periods.     

Fetal growth and development of the coypu (Myocastor coypus): Prenatal growth,tooth eruption,and cranial ossification

We examined the fetal growth and development of the coypu (Myocastor coypus), a member of the Caviomorpha that produces extremely precocial young. Analyses of 69 fetuses derived from the latter half of the prenatal period (60–125 days of gestation) focused on external feature growth and development, tooth eruption, and cranial ossification. There were four developmental stages based on morphological characteristics; major external changes predominated over somatic growth in the early stages by 100–105 days of gestation, whereas the last stage was a time of rapid somatic growth. Growth rate was greater in hind foot length (4.3) than in fore foot length (3.4). Soft X-ray photos from 120 to 125 days of gestation show that the incisors, premolars, and first molars were completely calcified, and the second molars were present in the alveolus but not completely calcified. The occlusal surfaces of these teeth were subjected to wear. We analyzed the bone and cartilage of the coypu fetal cranium using a double-staining method. Early ossification of the jugular processes of the occipital bone was a prominent feature of coypu development. The digastric muscle originates on the jugular process, and early ossification should be linked to an adaptation to the herbivorous habit of weaned young coypu. Additionally, the sizes and closure times of six fontanelles are correlated with gestational age and are suggested as a comparative parameter for fetal maturity within and between mammalian species.     

Strongyloides myopotami (Secernentea: Strongyloididae) from the Intestine of Feral Nutrias (Myocastor coypus) in Korea

Surveys on helminthic fauna of the nutria, Myocastor coypus, have seldom been performed in the Republic of Korea. In the present study, we describe Strongyloides myopotami (Secernentea: Strongyloididae) recovered from the small intestine of feral nutrias. Total 10 adult nutrias were captured in a wetland area in Gimhae-si (City), Gyeongsangnam-do (Province) in April 2013. They were transported to our laboratory, euthanized with ether, and necropsied. About 1,300 nematode specimens were recovered from 10 nutrias, and some of them were morphologically observed by light and scanning electron microscopies. They were 3.7-4.7 (4.0±0.36) mm in length, 0.03-0.04 (0.033) mm in width. The worm dimension and other morphological characters, including prominent lips of the vulva, blunted conical tail, straight type of the ovary, and 8-chambered stoma, were all consistent with S. myopotami. This nematode fauna is reported for the first time in Korea.