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.     

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.     

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.     

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.     

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.     

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。     

Pre-implantational timetable of embryonal development of Myocastor coypus (Coypu)

The purpose of the present study was to determine the chronology of the pre-implantation embryonic development in Myocastor coypus (coypu). It was carried out by daily colpocytological examination and controlled mating of 33 females. Oocytes and embryos were obtained by flushing from day 0 to day 10 post-coitus (p.c.). On day 1 p.c., oocytes predominated whereas on day 2 p.c. zygotes were predominant. The cleavage period was from day 3 to day 6 p.c.. Morulae were collected from day 6 to day 9 p.c., whereas blastocysts were collected on days 8 and 9. From oviduct flushing, the embryos in the zygote stage and up to the morula stage with less than a 30-cell stage were recovered. Embryos in the morula stage with 30 or more cells and up to the growing blastocyst stage were collected from the flushing of hemiuteri.     

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.     

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.     

Population dynamics and regulation in the coypu Myocastor coypus in central Italy

A capture-recapture design was applied between January 1989 and June 1991 in a 37 5 ha area located in the central valley of the Tiber River (Latium), aimed at estimating the demographic parameters of a coypu population in the Mediterranean climate and at preliminarily investigating the factors that regulate its numbers in this region The population fluctuated between 27 and 137 individuals and followed a seasonal pattern It decreased after the winter and increased between summer and winter Density remained almost stable during a particularly mild winter Survival rates remained relatively high over the entire study period, reproductive activity and additions to the population from in situ reproduction, however, showed minimum peaks following colder winters Evidence of immigration was detected during periods of increasing density Key factor and preliminary density dependence analyses showed that pregnancy failure and newborn losses are cumulatively the most important factor contributing to varation in total mortality, and are positively related to coypu numbers in previous periods The failure to realize maximum potential fecundity is inversely related to previous coypu abundance We show that post-recruitment losses play only a minor role in determining population decline     

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.     

Regional differences in hindgut structure and function in the nutria,Myocastor coypus

Summary Morphologically the large intestine of the nutria resembles that of other caviomorphs, notably the guinea pig. The cecum is voluminous: it contributes 8.6% of the total intestinal length and 12.7% of the total intestinal surface area (considering the surface enlargement factor). It contains 27–32% of the wet ingesta and 20–23% of the dry matter in the gastrointestinal tract. In the colon the corresponding figures are: 21.8% of length, 12.6% of surface area, 16–21% of wet ingesta, and 16–40% of dry matter. The colon can be subdivided both structurally and functionally into two sections, the proximal and the distal colon, the border between the two being the apical flexure of a long parallel loop. The proximal colon (42% of colonic length) displays on the mucosal surface of its mesenterial side a narrow furrow bordered by ridges, which is absent in the distal colon. The ridges contain subepithelial accumulations of coiled tubuloalveolar mucoid glands, entwined by bundles of muscle fibers. Determinations of nitrogen in the contents near the furrow suggest a concentration of bacteria in this part of the lumen. It is hypothesized that the structural differentiations of the proximal colon provide mechanisms for the transport of bacteria from the proximal colon back into the cecum to maintain the fermentation function. The slopes of the longitudinal profiles for dry matter and for concentrations of sodium, potassium and calcium in the luminal contents change at the tip of the parallel loop. The electrical potential difference intestinal lumen — blood is particularly large in the proximal colon, indicating active electrogenic ion transport in this region. SEF surface enlargement factor - CSM colonic separation mechanism - PEG polyethylene glycol - DM dry matter Dedicated to Prof. K.-E. Wohlfarth-Bottermann, Institut für Cytologie und Mikromorphologie der Universität Bonn, Bonn, Federal Republic of Germany, on the occasion of his 65th birthday