“Measure my teeth and you'll know what I ate”: The molar ratio method and an updated interpretation of the diet of Nyctereutes sinensis (Carnivora,Canidae)

The molar ratio method presented by Acta Zoologica (98, 2016, 292) is a valid way to estimate the dietary differences between extant subspecies of the raccoon dog genus, Nyctereutes. Particularly, higher values of the molar ratio implies more omnivous diet than lower ones. With the same technique is possible to infer variations in the diet of extinct species. For the two Plio-Pleistocene fossil species Nyctereutes sinensis and Nyctereutes megamastoides, the authors estimate a more carnivorous diet for the latter in comparison to the former that has much higher values. This fact contrast with the morphological features of these two highly comparable species, often considered as morphotypes of the same species. Thanks to the revision of a large sample of N. sinensis from Chinese localities of the Yushe Basin (Shanxi Province), new scores for this species have been calculated. The results presented here confirms a strong adaptation to an omnivorous diet, as emerged from morphofunctional evidence in recent literature.     

Raccoon dog scent marking by scats and its significance in social behaviour

Utilization pattern of latrines by raccoon dogs,Nyctereutes procyonoides viverrinus, was studied on a small island in western Kyushu, Japan. Seventy-eight latrines were spread over the study areas, these were mainly formed on the flat surface in woody areas. Although the site and number of latrines were fairly stable throughout the year, distribution of the utilized latrines and number of scats per latrine were changed seasonally. Latrines were grouped into several clusters and communal utilization of latrines by several animals was observed within the cluster. Seasonal changes of utilization pattern observed in communal utilization rate and cluster formation was assumed to be caused by the changing of the social unit of raccoon dogs. Familiarization within the home range and information site to conspecifics may be concluded as the function of latrines.     

Dispersal of the alien raccoon dog Nyctereutes procyonoides in Southern Brandenburg, Germany

The raccoon dog Nyctereutes procyonoides, an East Asian canid species, was introduced into the European part of the former USSR since 1928. Within 50 years (1935–1984), it colonised a territory of 1.4 million km² in Europe. A telemetry study took place in Southern Brandenburg in a 60 km² sized study area with a typical mosaic structured East German agricultural landscape. For catching raccoon dogs, 20 trap boxes were set there in an area of 46 km², and between February 2001 and July 2004, 15 (5 males, 10 females) adult and 46 (25 males, 21 females) juvenile raccoon dogs were eartagged and adults additionally fitted with radio collars (Biotrack, 150–151 MHz). Data on dispersal behaviour was collected by the relocation points of 11 juveniles (6 males, 5 females). Four juvenile males dispersed even more than 40 km from their trapping places. Additionally, dispersal of two adult males could be documented. This behaviour probably indicates that the German raccoon dog population still is in a process of colonising. This canid’s ability for colonising spacious and distant areas during comparative short periods of time and its preference for habitats with richness of water possibly make this species to be an important vector of fox tapeworm Echinococcus multilocularis—a very dangerous zoonosis.     

Seasonal and annual variation in the diet of the raccoon dogNyctereutes procyonoides in northern Belarus: the role of habitat type and family group

To study variation in the diet of the raccoon dogNyctereutes procyonoides Gray, 1834 in northern Belarus, 3299 scats were sampled from 18 localities differing in habitat quality. In one of the 18 localities, the dietary study was conducted for nine years. The data obtained was analysed according to seasonality, between-year difference, family specificity and habitat influence. In northern Belarus, the raccoon dog was found to be a generalist predator with omnivorous and opportunistic feeding habits. Their diet was highly variable, but a common trait was specialization on carrion in winter and on berries in late summer. Beside carrion and berries, the other seasonally important food items were frogs, insects, plant matter, mammals, and birds. The diet varied between seasons and habitats. In the warm season, habitat factors, such as type of soil (clay or sand), proportion of lakes and open grassy marshes, seemingly determine the food supply for raccoon dogs, and thereby influence the diet of individuals. The obtained results on dietary variation of raccoon dogs can be used in detailed analysis of the impact of this introduced species on native fauna and its role in functioning of vertebrate communities.     

New insights on Early Pleistocene Nyctereutes from the Balkans based on material from Dafnero-3 (Greece) and Varshets (Bulgaria)

The study examines the taxonomy of the newly excavated Nyctereutes material from Dafnero-3 (Greece) and the unpublished specimens from Varshets (Bulgaria). One cranium and a hemimandible from Dafnero-3 site are ascribed to the species Nyctereutes megamastoides, already known from Dafnero-1 and other Early Pleistocene sites of Greece. Two additional crania and a hemimandible from Dafnero-3, along with the Varshets dental material are attributed to N. tingi. This species was previously reported in the Early Pliocene Megalo Emvolon fauna of northern Greece but the record has been challenged and a review is provided. The new findings of Dafnero-3, and Varshets, extend the presence of N. tingi in southeastern Europe until the beginning of the middle Villafranchian and confirm the geographic expansion of the taxon towards West. Moreover, the co-existence of N. tingi and N. megamastoides in Dafnero-3 is reported for the first time in Europe. A paleoecological analysis based on the lower molar method agrees with the existing hypothesis of a more omnivorous N. megamastoides and a more carnivorous N. tingi ecomorph, which further justifies their local co-existence. Additionally, the quantitative analyses of N. tingi from Dafnero-3, and Varshets reveal a possible succession from N. tingi to N. vulpinus, as already supported by previous studies.     

Seroprevalence of antibodies to Neospora caninum in dogs and raccoon dogs in Korea

Neospora caninum is an important cause of abortion in cattle, and dogs are its only known definitive host. Its seroprevalence among domestic urban and rural dogs and feral raccoon dogs (Nyctereutes procyonoides koreensis) in Korea was studied by indirect fluorescent antibody test (IFAT) and by the neospora agglutination test (NAT), respectively. Antibodies to N. caninum were found in 8.3% of urban dogs and in 21.6% of dogs at dairy farms. Antibody titers ranged from 1:50 to 1:400. Antibodies to N. caninum were found in six (23%) of 26 raccoon dogs. However, the potential role of raccoon dogs as a source of horizontal transmission of bovine neosporosis needs further investigation. The results of this study suggest that there is a close relationship between N. caninum infection among dairy farm dogs and cattle in Korea. This study reports for the first time upon the seroprevalence of N. caninum infection in raccoon dogs in Korea.     

Arthrostoma miyazakiense (Nematoda: Ancylostomatidae) infection in raccoon dogs of Korea and experimental transmission to dogs

Arthrostoma miyazakiense (Nematoda: Ancylostomatidae) is a hookworm species reported from the small intestines of raccoon dogs (Nyctereutes procyonoides) in Japan. Five Korean raccoon dogs (N. procyonoides koreensis) caught from 2002 to 2005 in Jeollanam-do (Province), a southeastern area of South Korea, contained helminth eggs belonging to 4 genera (roundworm, hookworm, whipworm, and Capillaria spp.) and cysts of Giardia sp. in their feces. Necropsy findings of 1 raccoon dog revealed a large number of adult hookworms in the duodenum. These hookworms were identified as Arthrostoma miyazakiense based on the 10 articulated plates observed in the buccal capsule and the presence of right-sided prevulval papillae. Eggs of A. miyazakiense were 60-65 x 35-40 micrometer (av. 62.5 x 35 micrometer), and were morphologically indistinguishable from those of Ancylostoma caninum. The eggs were cultured to infective 2nd stage larvae via charcoal culture, and 100 infective larvae were used to experimentally infect each of 3 mixed-bred puppies. All puppies harbored hookworm eggs in their feces on the 12th day after infection. This is the first report thus far concerning A. miyazakiense infections in raccoon dogs in Korea, and the first such report outside of Japan.     

Morphological variation of the Japanese raccoon dog: implications for geographical isolation and environmental adaptation

To test the effect of geographical isolation by 'Blakiston's Line' and the possibility of Bergmann's rule being valid, we comparatively examined the morphology of the crania, mandible and teeth of two subspecies of raccoon dog allopatrically distributed in Japan: Nyctereutes procyonoides albus and Nyctereutes procyonoides viverrinus . The Blakiston's Line is a biogeographic border separating mammalian and avian fauna in Japan, including N. p. albus and N. p. viverrinus . Most skull measurements of N. p. albus were larger than those of N. p . viverrinus , suggesting that the body size of N. p. albus could also be larger than that of N. p . viverrinus . Both subspecies were clearly isolated by Blakiston's Line and followed Bergmann's rule, with skulls of the northern subspecies, N. p. albus , larger than N. p. viverrinus . Premolars and molars of N. p. viverrinus were larger than those of N. p. albus , suggesting that N. p. viverrinus may be more frugivorous. The narrow postorbital constriction associated with development of temporal muscles in N. p. albus suggests this subspecies is more carnivorous.     

Evolutionary and biogeographical implications of variation in skull morphology of raccoon dogs (Nyctereutes procyonoides,Mammalia: Carnivora)

Morphological characteristics reflect geographical variation resulting from adaptation to varying environmental conditions. Carnivore species distributed over a wide geographical range generally have highly polymorphic morphological variation. The raccoon dog (Nyctereutes procyonoides) has a longitudinal distribution restricted to East Asia and the northern Indochina Peninsula. Its unique geographical range makes it an appropriate model to examine how morphological differences are influenced by geography. To demonstrate morphological evolution of Russian, Chinese, Korean and Japanese raccoon dogs predicted by geographical differences, we tested the island rule and Bergmann's rule. We compared craniodental variation among populations and examined morphological implications for intraspecific taxonomic status. Insular raccoon dogs possessed substantially smaller body size than those from the mainland. Moreover, different island effects among Japanese islands were demonstrated by markedly larger occipital condyle breath in the Hokkaido population. Larger skull size in Russian and Hokkaido raccoon dogs could be explained by Bergmann's rule. Based on previous chromosomal and molecular studies and results of our morphological analyses, we suggest Japanese raccoon dogs are a distinct species from the mainland N. procyonoides.     

Trichodectes canis (De Geer, 1778) (Phthiraptera, Ischnocera), a new ectoparasite of the raccoon dog (Nyctereutes procyonoides) in the Czech Republic

The raccoon (Nyctereutes procyonoides) is described as a host of the dog biting louse, Trichodectes canis (De Geer, 1778). The present note reports the occurrence of this species of louse on two raccoon dogs from Moravia and Bohemia. The specimens of T. canis collected on this host differed from T. canis originating from the domestic dog by body size only.     

Regulation of energy economy in raccoon dogs and blue foxes: a process of dynamic interactions

1. Seasonal regulation of energy economy was studied in farm-raised blue foxes (Alopex lagopus) and raccoon dogs (Nyctereutes procyonoides; Gray, 1834). 2. Both species exhibited marked seasonal changes in body weight, body energy content, food intake and locomotor activity. Seasonal changes in food efficiency were also evident. 3. The results emphasize the important role of both energy intake and energy expenditure in the regulation process. 4. It can be concluded that regulation of seasonal energy balance is a dynamic process with various interactions between different factors.     

The evolution of Nyctereutes (Carnivora: Canidae) in the Nihewan Basin,Hebei, northern China

The occurrence of Nyctereutes during the Plio-Pleistocene has long been reported in northern China, with the highest abundance in the Nihewan Basin. However, due to site dispersal, the coexistence of different taxa, and lack of a precise stratigraphic constraint, the evolutionary process of this genus remains enigmatic. In this study, we re-examined the available Nyctereutes materials recovered from the Nihewan Basin housed in IVPP and Tianjin Natural History Museum, in addition to a newly recovered specimen from our latest excavation. Furthermore, we compared these materials with Nyctereutes fossils recovered from the Pleistocene Zhoukoudian sites near Beijing and the extant species N. procyonoides. Our analysis of the upper molar morphometry reveals the variations in size and dietary characteristics within different species of Nyctereutes during the late Plio-Pleistocene. The examination of molars indicates an increase in the size of Nyctereutes sinensis compared to early Pliocene N. tingi as well as changes in the molar teeth morphology. Subsequently, changes in diet or environmental factors possibly caused the decrease of body size in the late Pleistocene. We also estimate an age constraint for the fossils of N. sinensis from the Xiashagou section by relocating Licent's localities and referring of updated magnetostratigraphic data.     

Euryhelmis squamula (Digenea: Heterophyidae) Recovered from Korean Raccoon Dog,Nyctereutes procyonoides koreensis,in Korea

In this study, we intended to describe an unrecorded species of heterophyid trematode recovered from the small intestine of a Korean raccoon dog, Nyctereutes procyonoides koreensis, in Korea. A total of 13 small flukes were collected from a deceased Korean raccoon dog which was found in Chuncheon-si, Gangwon-do, Korea in May 2017. The trematode body were covered with many small spines, rectangular, broader than long, 807–1,103 μm long and 1,270–1,550 μm wide. Oral sucker in the anterior end slightly smaller than acetabulum. Pharynx muscular and well developed. Esophagus relatively long and sigmoid. Acetabulum small and located at median in anterior 2/5 portion. Ceca bifurcated at the anterior of genital pore and acetabulum and terminated at testis level. Testes larger, deeply lobed and located at the near of posterior end of body. Ovary small, triangular and located at the slight left of median and the anterior of left testis. Vitelline follicles dendritic and extend from the middle level of esophagus to the posterior portion of body. Eggs embryonated, operculated, small and 33–35×15–16 μm in size. Based on the morphological characteristics, the small heterophyid flukes recovered from the small intestines of Korean raccoon dog, N. procyonoides koreensis, were identified as Euryhelmis squamula (Digenea: Heterophyidae). Accordingly, this species of heterophyid flukes is to be a new trematode fauna in Korea by this study.     

Overwintering strategy of wild free-ranging and enclosure-housed Japanese raccoon dogs (<Emphasis Type="Italic">Nyctereutes procyonoides albus</Emphasis>)

The raccoon dog, Nyctereutes procyonoides, is a canid with a passive overwintering strategy in northern Europe. However, the behaviour and physiology of the Japanese subspecies, N. p. albus, which has fewer chromosomes than the other subspecies, remain unknown. We measured body temperature, body composition and blood biochemistry of wild free-ranging and fasted enclosure-housed N. p. albus during boreal winter in Hokkaido, Japan. Body temperature of N. p. albus decreased from 38°C in autumn to 35.9–36.7°C while maintaining a circadian rhythm in late February (n = 3). A transient 18–36% decrease in resting heart rate occurred when body temperature was low (n = 2). Despite a 33–45% decrease in body weight due to winter fasting, circulating glucose, total protein and triglyceride levels were maintained (n = 4). Serum urea nitrogen dropped by 43–45% from autumn to spring, suggesting protein conservation during fasting. The overwintering survival strategy of N. p. albus in central Hokkaido is based upon large changes in seasonal activity patterns, winter denning and communal housing without the large decrease in body temperature that is characteristic of subarctic animals exhibiting hibernation or torpor. Naoya Kitao, Daisuke Fukui and Peter G. Osborne contributed equally to this work     

Seasonal physiology of the wild raccoon dog (Nyctereutes procyonoides)

The raccoon dog (Nyctereutes procyonoides) is a canid omnivore with autumnal fattening and winter sleep. Farmraised raccoon dogs have elevated plasma leptin and growth hormone levels in the winter and depressed plasma cortisol and insulin concentrations during wintertime food deprivation. However, these parameters were not previously tested in the wild population. In the present study 37 wild raccoon dogs were sampled at different seasons and diverse biochemical variables were determined. The results mostly confirmed previous observations on farmraised raccoon dogs. The liver glycogen stores increased during the autumnal fattening period but were low in the winter. The liver glycogen phosphorylase activity decreased but lipase activity increased in the winter indicating the use of fat as the principal metabolic fuel. The plasma insulin concentrations were low in the winter allowing the release of fatty acids from adipose tissue. Low wintertime cortisol and thyroid hormone levels could contribute to protein sparing. Unlike on farms, wild raccoon dogs did not show seasonal fluctuations in their plasma ghrelin or growth hormone levels. The observed physiological phenomena emphasise the adaptation of the species to long periods of food scarcity in the winter.     

Adaptations of the raccoon dog (Nyctereutes procyonoides) to wintering--effects of restricted feeding or periodic fasting on lipids, sex steroids and reproduction

The raccoon dog (Nyctereutes procyonoides) is an omnivorous canid with autumnal hyperphagia and fattening followed by mid-winter passivity and fasting in boreal latitudes with seasonal snow cover. The effects of two different feeding levels (400 or 200 kcal/animal/d) or fasting (5-week fasting+1-week feeding+3-week fasting) on plasma lipids, sex steroids and reproductive success of farm-bred raccoon dogs (n=60 females and 24 males) were studied in winter. The body masses, body mass indices (BMIs) and levels of plasma triacylglycerols (TG), total cholesterol and low- and high-density lipoprotein cholesterol did not differ between the fed and the restrictively fed animals. During fasting, the plasma TG concentrations increased and the BMIs decreased, indicating the release of fatty acids from adipose tissue. After the fasting periods, the levels of plasma cholesterol and high-density lipoprotein cholesterol increased, whereas the TG levels decreased indicating the rebuilding of energy reserves. The fact that the different wintertime feeding regimes had no impact on the plasma glucose, total protein, cortisol, estradiol, progesterone or testosterone levels, or on the reproductive success, indicates versatile adaptive capacity in the species.     

Endocrine response to fasting in the overwintering captive raccoon dog (Nyctereutes procyonoides)

The raccoon dog (Nyctereutes procyonoides) is an omnivorous canid utilizing the passive wintering strategy in the boreal climate. Farmed raccoon dogs (n=12) were randomly assigned into two study groups on 26 November 2003. Between 3 December 2003 and 27 January 2004, half of the animals were fasted for 8 weeks and plasma weight-regulatory hormone concentrations determined on 26 November and 30 December 2003 and on 27 January 2004. The plasma peptide YY, ghrelin, and growth hormone (GH) concentrations increased due to food deprivation, while the T4 and Acrp30 concentrations decreased. Furthermore, the plasma GH concentrations were higher in the fasted raccoon dogs than in the fed animals, which had higher plasma insulin, glucagon, and T4 concentrations. However, fasting had no effect on the plasma leptin concentrations. The results confirm previous findings with unchanged leptin levels in fasting carnivores. Increased GH levels probably contribute to increased lipolysis and mobilization of fat stores. Ghrelin can also enhance lipolysis by increasing the GH levels. The decreased levels of T4 may reduce the metabolic rate. The plasma dopamine concentrations decreased due to fasting unlike observed previously in rats. Together with the unaffected adrenaline, noradrenaline, and cortisol concentrations, this suggests that food deprivation in winter does not cause stress to the raccoon dog but is an integral part of its natural life history.     

The diet of feral raccoon dog (<Emphasis Type="Italic">Nyctereutes procyonoides</Emphasis>) and native badger (<Emphasis Type="Italic">Meles meles</Emphasis>) and red fox (<Emphasis Type="Italic">Vulpes vulpes</Emphasis>) in Denmark

The raccoon dog (Nyctereutes procyonoides) is an East Asian Canid that has been introduced in Europe. Introduction of alien species is an increasing conservation issue. We examined the diet of a recently established raccoon dog population in Denmark by analysing stomach content in 249 carcasses collected in 2008–2016. Raccoon dog diet was compared to the diet of native badger (Meles meles) and red fox (Vulpes vulpes) in Denmark. The most common food for raccoon dogs were invertebrates (frequency of occurrence, FO 69%), small mammals (FO 68%), birds (FO 41%), fruits (FO 38%), amphibians (FO 36%) and carrions (FO 34%). The occurrence of invertebrates was highest during spring and summer, while fruits, cereals and carrions were eaten most often during autumn and winter. As expected, raccoon dog shared the major food categories with badger and red fox, but generally, it had a wider dietary niche. Overall, dietary overlap between raccoon dog and badger was 0.74 (Pianka index, O_jk). The dietary overlap with red fox was relatively high in all seasons, peaking in summer (O_jk 0.87) and dropping in winter (O_jk 0.79). Despite the dietary overlap between the alien racoon dog and native red fox and badger, the species may coexist due to partitioning of feeding habitats and/or because the red fox is limited by other factors, e.g. diseases and anthropogenic activities. The introduced raccoon dog seems to fit a dietary niche between badger and red foxes in human-dominated landscapes in north-western Europe.     

Modelled population growth based on reproduction differs from life tables based on age determination in Danish raccoon dogs ( Nyctereutes procyonoides )

The population of raccoon dogs (Nyctereutes procyonoides) in Denmark has increased rapidly from 1995 when the first was recorded until today where 3291 raccoon dogs are trapped, shot by hunters or road killed. The aims of this study are to present the first data on reproduction and life tables of raccoon dogs in Denmark and to compare mortality from modelled life tables with game bag records and sampled raccoon dogs in different age groups. In this study, the uteri of 89 adult females (> 10 months) were examined for placental scars (PSC), and 561 individuals (289 males, 272 females) were aged using pulp cavity width and dental lines in canine teeth. The litter size of raccoon dogs in Denmark is to date the largest litter size recorded in the wild (mean ± SE) 10.8 ± 0.4, range 1–16 pubs and fecundity 8.4 ± 0.6 pubs. The percent-reproducing females are 78–83%, based on dark and all PSC, respectively. A significant difference was found between the proportion of individuals composing the different age groups based on age determination of individuals collected (Ntage) and the modelled number of individuals in age groups based on fecundity and different mortality rate (Ntmodel), X2 = 8, p < 0.05. The discrepancy between the relatively high reproduction and lifetables may be due to older and more experienced animals that avoid culling. A low population density in a newly founded Danish population of raccoon dogs, together with a milder climate where raccoon dogs can forage during the winter, may cause an exceptionally high reproduction in Danish raccoon dogs.