Going west—invasion genetics of the alien raccoon dog Nyctereutes procynoides in Europe

Dietary change influences the composition of the fecal microbiota in two rescued wild raccoon dogs (Nyctereutes procyonoides)

The gut microbiota of wild animals, influenced by various factors including diet, nutrition, gender, and age, plays a critical role in their health and disease status. This study focuses on raccoon dogs (Nyctereutes procyonoides), a commonly found wild animal, and its gut microbiota composition in response to dietary shifts. The study aimed to compare the fecal bacterial communities and diversity of rescued raccoon dogs fed three different diet types (fish and amphibians, mixed protein with maize, and solely maize) using high-throughput sequencing. Results indicated that the dietary composition significantly influenced the gut microbiota, with notable differences in the abundance of several key phyla and genera. The study identified Firmicutes as the dominant phylum in all diet groups, with notable variations in the relative abundances of Bacteroidota, Proteobacteria, and Verrucomicrobiota. Notably, the group solely fed maize exhibited a significant increase in Proteobacteria, potentially linked to dietary fiber and lignin degradation. The genus-level analysis highlighted significant differences, with Lactobacillus and Bifidobacterium responding to dietary shifts. The genus Akkermansia in Verrucomicrobiota can be identified as a marker for assessing the health of the gut and deserves further investigation. Gender-specific differences in the gut microbiota were observed, highlighting the influence of individual variation. Furthermore, the analysis of bacterial functions suggested a connection between diet and host metabolism, emphasizing the need for further research to understand the complex mechanisms underlying the relationship between dietary composition and gut microbiota in wild animals. These findings provide crucial insights into conservation and rescue efforts for wild animals.

Toxocara tanuki larval distribution in mice and the infectivity of tissue larvae

Toxocara tanuki is a common large roundworm in raccoon dogs. Experimental infection studies of T. tanuki in mice were conducted to clarify the distribution and infectivity of larvae in tissue. Groups of BALB/c and C57BL/6 mice (n = 5 mice/group) were each inoculated with 1000 embryonated T. tanuki eggs and necropsied at 7, 31, 91, and 182 days post inoculation (dpi). The number of larvae in the central nervous system, heart, lungs, kidneys, spleen, gastrointestinal tract, liver, and carcass was examined. Larvae obtained from the aforementioned mice on different days of the necropsy were orally inoculated into four groups of ICR mice (n = 6 mice/group) that were then necropsied at 21 dpi. Larvae were recovered from all mice. In the BALB/c and C57BL/6 mice, most of the larvae (> 88.7%) were recovered from the liver and the remainder from other tissues. The total number of larvae recovered from C57BL/6 mice was significantly higher than that from BALB/c mice, but no difference in the relative larval distribution within the viscera between the two mouse strains was observed. The mean recovery percentage of larvae from ICR mice infected with 182-day-old tissue larvae was 3.3%. Our findings showed that T. tanuki larvae migrated predominantly to the liver of mice and that the larvae maintained their infectivity for at least half a year.

Introduction, spread, and impacts of invasive alien mammal species in Europe

Biological invasions have emerged as one of the main drivers of biodiversity change and decline, and numbers of species classed as alien in parts of their ranges are rapidly rising. The European Union established a dedicated regulation to limit the impacts of invasive alien species (IAS), which is focused on the species on a Union List of IAS of particular concern. However, no previous study has specifically addressed the ecology of invasive alien mammals included on the Union List.We performed a systematic review of published literature on these species. We retrieved 262 publications dealing with 16 species, and we complemented these with the most up-to-date information extracted from global databases on IAS.We show that most of the study species reached Europe as pets and then escaped from captivity or were intentionally released. On average each year in the period 1981-2020, 1.2 species were recorded for the first time as aliens in European countries, and most species are still expanding their alien ranges by colonising neighbouring territories. France is the most invaded nation, followed by Germany, Italy, and the Russian Federation, and the muskrat Ondatra zibethicus, the American mink Neovison vison, and the raccoon dog Nyctereutes procyonoides are the most widespread species, having invaded at least 27 countries each. Invasive mammals of European Union concern are threatening native biodiversity and human well-being: worryingly, 81% of the 16 study species are implicated in the epidemiological cycle of zoonotic pathogens.Containing secondary spread to further countries is of paramount importance to avoid the establishment of new populations of invasive mammals and the related impacts on native communities, ecosystem services, and human health.We present a compendium on the ecology and impacts of invasive mammals of European Union concern. It can be used to assist environmental policies, identify and subsequently fill knowledge gaps, and inform stakeholders.

The ecology of zoonotic parasites in the Carnivora

The order Carnivora includes over 300 species that vary many orders of magnitude in size and inhabit all major biomes, from tropical rainforests to polar seas. The high diversity of carnivore parasites represents a source of potential emerging diseases of humans. Zoonotic risk from this group may be driven in part by exceptionally high functional diversity of host species in behavioral, physiological, and ecological traits. We review global macroecological patterns of zoonotic parasites within carnivores, and explore the traits of species that serve as hosts of zoonotic parasites. We synthesize theoretical and empirical research and suggest future work on the roles of carnivores as biotic multipliers, regulators, and sentinels of zoonotic disease as timely research frontiers.

Predicting the zoonotic capacity of mammals to transmit SARS-CoV-2

Back and forth transmission of SARS-CoV-2 between humans and animals may lead to wild reservoirs of virus that can endanger efforts toward long-term control of COVID-19 in people, and protecting vulnerable animal populations that are particularly susceptible to lethal disease. Predicting high risk host species is key to targeting field surveillance and lab experiments that validate host zoonotic potential. A major bottleneck to predicting animal hosts is the small number of species with available molecular information about the structure of ACE2, a key cellular receptor required for viral cell entry. We overcome this bottleneck by combining species' ecological and biological traits with 3D modeling of virus and host cell protein interactions using machine learning methods. This approach enables predictions about the zoonotic capacity of SARS-CoV-2 for over 5,000 mammals - an order of magnitude more species than previously possible. The high accuracy predictions achieved by this approach are strongly corroborated by in vivo empirical studies. We identify numerous common mammal species whose predicted zoonotic capacity and close proximity to humans may further enhance the risk of spillover and spillback transmission of SARS-CoV-2. Our results reveal high priority areas of geographic overlap between global COVID-19 hotspots and potential new mammal hosts of SARS-CoV-2. With molecular sequence data available for only a small fraction of potential host species, predictive modeling integrating data across multiple biological scales offers a conceptual advance that may expand our predictive capacity for zoonotic viruses with similarly unknown and potentially broad host ranges.

Detection of larvae of Toxocara cati and T. tanuki from the muscles of free-ranging layer farm chickens

Although raw or undercooked livestock meat or viscera has been suggested to be a source of human toxocariasis, there have been few reports on the prevalence of Toxocara larvae in the tissue of livestock animals. To investigate the presence of Toxocara larvae in chickens, we examined 50 culled chickens from a commercial layer farm. The liver, breast meat, and thigh meat were separated individually and artificially digested to examine for the presence of larvae. Nematode larvae were detected in 2 out of 50 chickens. One larva was detected from the breast meat, and it was molecularly identified as Toxocara tanuki. The other from the thigh meat of another chicken was molecularly identified as Toxocara cati. The present study demonstrated for the first time that T. tanuki larvae do infect chickens in the natural environment. The fact that Toxocara spp. larvae were found in muscles of farm chickens suggests that consumption of raw or undercooked chicken meat may present a risk for human toxocariasis.

Phylogenetic relationships between different raccoon dog (Nyctereutes procyonoides) populations based on four nuclear and Y genes

BACKGROUND

The raccoon dog (Nyctereutes procyonoides), endemic to East Asia, is classified as six subspecies according to their geographical distribution including a population introduced to Europe. Studies on phylogenetic relationship or population genetics in both native and introduced areas have been carried out recently. Lately, opinions that Japanese raccoon dogs should be classified as a different species were asserted based on several studies using karyotypes, morphometric characters, mtDNA, and microsatellites analysis. However, no data pertaining to the nuclear DNA (nDNA) or Y chromosome are available.

OBJECTIVE

To estimate the relationship among the species using different genes is necessary in understanding of the history of this species.

METHOD

Therefore, we investigated nDNA and Y chromosomes in our study to define relationships: (1) between continental raccoon dog populations, (2) between original and introduced groups, and (3) between continental and Japanese groups.

RESULTS

The analysis of four nuclear (CHRNA1, VTN, TRSP, WT1) and ZFY genes indicated that there had been no genetic differentiation among the continental populations. However, significant differences were observed between continental and Japanese raccoon dogs in VTN and ZFY genes implying genetic differentiation has been going between them.

CONCLUSION

To better understand the phylogenetic relationship among raccoon dog populations, further study will be necessary.

Molecular evolution of MHC class II DRB exon 2 in Japanese and Russian raccoon dogs, Nyctereutes procyonoides (Carnivora: Canidae)

Raccoon dogs, Nyctereutes procyonoides, are native to East Asia, but have been introduced into western Russia and eastern Europe. To determine allelic diversity and elucidate the evolution of major histocompatibility complex (MHC) class II genes in the raccoon dog, we analysed a 237-bp region of DRB exon 2 from 36 individuals of native and introduced populations from Japan and Russia. We detected 23 DRB alleles (Nypr-DRBs), 22 of which were novel. Some alleles were found across the species’ range, while others were geographically restricted. For both native and introduced populations, the ratio of non-synonymous to synonymous substitution rates for codons at predicted antigen-binding sites was significantly greater than 2, indicating that Nypr-DRBs have evolved under positive selection. Mixed effect model evolution analysis and an algorithm to detect recombination showed five positively selected codons and one recombination breakpoint, respectively. Overall, our results suggest that the diversity of MHC class II DRB in N. procyonoides was influenced and maintained by recombination, pathogen-driven positive selection, geographical barriers and the founder effect. A Bayesian phylogenetic tree revealed no evidence of trans-species polymorphism (TSP), but instead showed monophyly for the Nypr-DRB alleles within a larger clade of canid sequences. The lack of TSP may have been due to long-term divergence of raccoon dogs from other canids, or to their having encountered different sets of pathogens due to occupying a different ecological niche.

The occurrence and muscle distribution of Trichinella britovi in raccoon dogs (Nyctereutes procyonoides) in wildlife in the Głęboki Bród Forest District, Poland

The raccoon dog (Nyctereutes procyonoides) is an introduced, invasive species in Europe. Literature data show that raccoon dogs act as a reservoir of many dangerous parasites, including nematodes of the genus Trichinella. The aims of the study were to determine the prevalence of Trichinella spp. infection in raccoon dogs collected from the Głęboki Bród Forest District between 2013 and 2016, and to evaluate their distribution in the muscle tissue of the host. The larvae of Trichinella spp. were detected in 45 raccoon dogs (39.82%), and all of them were identified as T. britovi. No mixed infection was observed. The intensity of infection ranged from 0.02 to 622.92 larvae per gram (LPG), and the highest mean was observed in the tongue and lower forelimb in both examined sexes. The raccoon dog may play a significant role as a reservoir of T. britovi in the wildlife in the examined area.

Genetic Diversity and Population Structure of East Asian Raccoon Dog (Nyctereutes procyonoides): Genetic Features in Central and Marginal Populations

The raccoon dog (Nyctereutes procyonoides) is endemic to East Asia but has been introduced in Europe. Its high adaptability enabled its rapid colonization of European countries, where population growth has been raising concerns regarding ecosystem disturbance and the spread of zoonotic diseases. The genetic diversity and structure of endemic, source, and introduced populations from seven locations across South Korea, China, Russian Far East, Finland (spread to Finland after introduction to European part of Russia from Russian Far East), Vietnam, and Japan (Honshu and Hokkaido) were examined based on 16 microsatellite loci. Two major and significantly different (F_ST = 0.236) genetic clusters were found: continental (South Korean, Chinese, Russian, Finnish, and Vietnamese) and island (Japanese) populations. The continental raccoon dog population comprises three subpopulations (Chinese_Russian_Finnish, South Korean, and Vietnamese) and the Japanese population consists of Honshu and Hokkaido subpopulations. The genetic diversity and geographic structure of raccoon dogs in East Asia has been influenced by natural barriers to gene flow and reveals a typical central-marginal trend in genetic diversity (continental vs. island, and central vs. marginal or source vs. introduced within continental populations). The detected differences between continental and island populations agree with those reported in previous studies that considered these populations as different species.

Comparative Transcriptome Analysis of Raccoon Dog Skin to Determine Melanin Content in Hair and Melanin Distribution in Skin

The raccoon dog (Nyctereutes procyonoides) is an important canid fur-bearing animal species worldwide. Chinese raccoon dogs that present a white mutation, especially those with a white coat. Exploring melanin biosynthesis in the hair and skin of raccoon dogs is important for understanding the survival and evolutionary mechanisms of them. In this study, we measured the content of melanin in the hair of two types of raccoon dog and generated stained slices of skin tissue. The results indicated that melanin biosynthesis occurs in the wild-type (W) and white-type (B) raccoon dog skin, although less melanin is produced in B skin. We then sequenced the skin transcriptomes of W and B, compared the similarities and differences in expressed genes. A comparison of the gene expression showed 60 up-regulated genes and 127 down-regulated genes in B skin. We analyzed the unigenes and pathways related to the melanogenesis pathway and found that TYR, TYRP1, MC1R, SLC24a5, SLC45a2 and OCA2 were significantly down-regulated in B skin and these results were verified via qRT-PCR. We surmised that the phenotypic characteristics of the white mutation might be caused by the reduced expression of these genes and this finding provides new insights for future experiments in raccoon dogs.

Impact of anthropogenic pressure on the formation of population structure and genetic diversity of raccoon dog Nyctereutes procyonoides

The raccoon dog Nyctereutes procyonoides experienced an active introduction and acclimatization in the European part of Russia followed by its migration to and colonization in the neighboring countries. Eventually, it has spread rapidly into many European countries. N. procyonoides probably invaded Lithuania from the neighboring countries of Belarus and Latvia where the species was introduced. However, the data on genetic diversity and population structure of the raccoon dogs in the recently invaded territories are still scarce. The objectives of this study were to investigate genetic diversity of N. procyonoides in Lithuania after acclimatization, and to assess the impact of anthropogenic pressure on the formation of population structure. A total of 147 N. procyonoides individuals collected from different regions of Lithuania were genotyped using 17 microsatellite markers. The microsatellite analysis of raccoon dogs indicated high levels of genetic diversity within the population. The Bayesian clustering analysis in STRUCTURE identified 4 genetic clusters among sampled raccoon dogs that could not reveal a clear separation between subpopulations. The widespread distribution of raccoon dogs in Lithuania, high level of genetic variation observed within subpopulations, and low level of variation portioned among subpopulations suggest migration and gene flow among locations. The significant correlation between genetic and geographic distances indicated isolation that reflected the distance between locations. The fencing of highways and very intensive traffic could be barriers to gene flow between the western and eastern sampling areas of raccoon dogs.

Homogenous Population Genetic Structure of the Non-Native Raccoon Dog (Nyctereutes procyonoides) in Europe as a Result of Rapid Population Expansion

The extent of gene flow during the range expansion of non-native species influences the amount of genetic diversity retained in expanding populations. Here, we analyse the population genetic structure of the raccoon dog (Nyctereutes procyonoides) in north-eastern and central Europe. This invasive species is of management concern because it is highly susceptible to fox rabies and an important secondary host of the virus. We hypothesized that the large number of introduced animals and the species' dispersal capabilities led to high population connectivity and maintenance of genetic diversity throughout the invaded range. We genotyped 332 tissue samples from seven European countries using 16 microsatellite loci. Different algorithms identified three genetic clusters corresponding to Finland, Denmark and a large 'central' population that reached from introduction areas in western Russia to northern Germany. Cluster assignments provided evidence of long-distance dispersal. The results of an Approximate Bayesian Computation analysis supported a scenario of equal effective population sizes among different pre-defined populations in the large central cluster. Our results are in line with strong gene flow and secondary admixture between neighbouring demes leading to reduced genetic structuring, probably a result of its fairly rapid population expansion after introduction. The results presented here are remarkable in the sense that we identified a homogenous genetic cluster inhabiting an area stretching over more than 1500km. They are also relevant for disease management, as in the event of a significant rabies outbreak, there is a great risk of a rapid virus spread among raccoon dog populations.

Population genetic study of the raccoon dog (Nyctereutes procyonoides) in South Korea using newly developed 12 microsatellite markers

The raccoon dog (Nyctereutes procyonoides) is distributed from southeastern Siberia to northern Vietnam, including Korea and Japan, as well as Europe. In Korea, most of its predators and competitors are extinct, which has resulted in rapid growth of the raccoon dog population. This population increase has raised concerns about its role in the ecosystem and the zoonotic transfer of various contagious diseases, and thus an effective method of raccoon dog population control in Korea is required. To investigate the genetic diversity and structure of raccoon dog populations, 12 polymorphic microsatellite loci were identified and characterized. These novel microsatellite markers were employed to obtain basic population genetic parameters for 104 N. procyonoides specimens from five locations in South Korea. The mean allele number of 12 loci across samples was 8.7, and the number of alleles per locus ranged 2-13. Mean expected and observed heterozygosities were 0.723 and 0.619, respectively. Genetic differentiation, estimated by pairwise FST, was significant for all population pairs excepting Seoul/Gyeonggi and Gangwon pair, with a moderate level of genetic differentiation for all the population pairs (mean FST = 0.054), but little differentiation between Seoul/Gyeonggi and Gangwon (FST = 0.024). Bayesian-based clustering analysis predicted that Korean raccoon dog population is composed of four distinct genetic subpopulations. These genetic information and structure of raccoon dog will be very useful to prevent spreading infectious diseases.