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The paradoxical extinction: Exploring signatures of assortative mating as a possible mechanism that maintains canonical Red Wolf genetic ancestry in the American Gulf Coast canids.

Admixed genomes, particularly those with an evolutionary history of genetic exchange with an endangered or extinct species, are valued for innovative and unconventional conservation actions. Here, we show the substantial conservation value that the admixed canids of the Gulf Coast have as they retain high amounts of contemporary Red Wolf ancestry and unique genetic variation of past Red Wolf lineages (e.g. ghost ancestry). We analyzed 54,439 loci genotyped across the genome of 413 North American canids and investigated the role that assortative mating with respect to ancestry proportions played in the retention of endangered genetic variation. We report high correlations of inter-chromosomal ancestry proportions that varied with geographic location along Texas and Louisiana Gulf Coast populations, with the stronger signatures reported in the latter. We found that models of assortative mating promoted greater ancestry variance compared with random mating leading to increased efficiency of selection for Red Wolf and ghost alleles. Despite the Red Wolf being extinct in the wild, original, and ghost genomic variation persists in Gulf Coast admixed canids. We suggest two conservation strategies that value and preserve this unique and endangered genomic variation through designed breeding programs. Ultimately the incorporation of this ghost genetic variation would be valuable to boost the genetic viability of the ex situ Red Wolf breeding program, create in situ redundancy, and avoid extinction for this endemic American wolf species.

Animals

Evolutionary consequences of domestication on the selective effects of new amino acid changing mutations in canids.

The domestication of wild canids led to dogs no longer living in the wild but instead residing alongside humans. Extreme changes in behavior and diet associated with domestication may have led to the relaxation of the selective pressure on traits that may be less important in the domesticated context. Thus, here we hypothesize that strongly deleterious mutations may have become less deleterious in domesticated populations. We test this hypothesis by estimating the distribution of fitness effects (DFE) for new amino acid changing mutations using whole-genome sequence data from 24 gray wolves and 61 breed dogs. We find that the DFE is strikingly similar across canids, with 26-28% of new amino acid changing mutations being neutral/nearly neutral (|s| < 1e-5), and 41-48% under strong purifying selection (|s| > 1e-2). Our results are robust to different model assumptions suggesting that the DFE is stable across short evolutionary timescales, even in the face of putative drastic changes in the selective pressure caused by artificial selection during domestication and breed formation. On par with previous works describing DFE evolution, our data indicate that the DFE of amino acid changing mutations depends more strongly on genome structure and organismal characteristics, and less so on shifting selective pressures or environmental factors. Given the constant DFE and previous data showing that genetic variants that differentiate wolf and dog populations are enriched in regulatory elements, we speculate that domestication may have had a larger impact on regulatory variation than on amino acid changing mutations.

Journal Article

Rapid derivation of cloning-competent cells from peripheral blood advances conservation biobanking.

Establishing viable cell lines from endangered species is essential for conservation, yet traditional fibroblast derivation from skin biopsies faces challenges including contamination risk and extended culture timelines. Here, we demonstrate that endothelial progenitor cells (EPCs) and pericytes isolated from peripheral blood represent robust alternatives to fibroblasts for biobanking. Compared to canid fibroblasts, canid blood-derived cells exhibit 2- to 3-fold faster doubling rates (15 to 20&#xa0;h vs. ~35&#xa0;h for fibroblasts) and reduced time to banked cell lines (1.5 to 2&#xa0;wks vs. 3 to 4&#xa0;wks for fibroblasts). Proteomic profiling of 32 canonical markers confirmed EPCs and pericytes represent distinct populations with lineage-specific molecular signatures. Optical genome mapping demonstrated equivalent genomic stability across cell types with no detectable structural variants or aneuploidies. Finally, interspecific somatic cell nuclear transfer (iSCNT) experiments confirmed both EPCs and pericytes generate viable canid embryos with efficiency meeting or exceeding fibroblasts. As a proof of concept for conservation cloning, iSCNT embryos made with gray wolf blood-derived cells had a 15% implantation rate following embryo transfer and resulted in six viable fetuses. These findings support integrating blood-derived cell banking into conservation programs, which enables opportunistic genetic preservation during standard management activities and expands options for genetic rescue through assisted reproductive technologies.

Animals

Skull morphology of the extinct Tasmanian tiger suggests unique biting style.

The recently extinct thylacine (Tasmanian tiger) was the largest modern marsupial predator. It is considered a classic example of evolutionary convergence due to striking similarities with placental canids (e.g., foxes and wolves), particularly in the skull, despite ~160 million years of evolutionary separation. However, we here present geometric and linear morphometric evidence that the thylacine's cranial form arises from a mosaic of traits not represented among canids or other living mammalian carnivores. Thylacines had disproportionately large heads, tall and gracile snouts with a flared canine region, and conspicuously large infraorbital foramina. Many of these traits suggest adaptations to fast, high-impact snapping behaviour in prey capture, as proposed for several living and extinct predatorial vertebrates with similar trait combinations. The thylacine's cranial function may therefore not be inferable from observation of living mammals. However, genomic progress presents new opportunities for future insights into the evolution and development of thylacine cranial adaptation.

Animals

High prevalence of PRDM9-independent recombination hotspots in placental mammals.

In many mammals, recombination events are concentrated in hotspots directed by a sequence-specific DNA-binding protein named PRDM9. Intriguingly, PRDM9 has been lost several times in vertebrates, and notably among mammals, it has been pseudogenized in the ancestor of canids. In the absence of PRDM9, recombination hotspots tend to occur in promoter-like features such as CpG islands. It has thus been proposed that one role of PRDM9 could be to direct recombination away from PRDM9-independent hotspots. However, the ability of PRDM9 to direct recombination hotspots has been assessed in only a handful of species, and a clear picture of how much recombination occurs outside of PRDM9-directed hotspots in mammals is still lacking. In this study, we derived an estimator of past recombination activity based on signatures of GC-biased gene conversion in substitution patterns. We quantified recombination activity in PRDM9-independent hotspots in 52 species of boreoeutherian mammals. We observe a wide range of recombination rates at these loci: several species (such as mice, humans, some felids, or cetaceans) show a deficit of recombination, while a majority of mammals display a clear peak of recombination. Our results demonstrate that PRDM9-directed and PRDM9-independent hotspots can coexist in mammals and that their coexistence appears to be the rule rather than the exception. Additionally, we show that the location of PRDM9-independent hotspots is relatively more stable than that of PRDM9-directed hotspots, but that PRDM9-independent hotspots nevertheless evolve slowly in concert with DNA hypomethylation.

Animals

Reference genomes of Japanese raccoon dog (Nyctereutes viverrinus) and a Japanese red fox (Vulpes vulpes japonica).

We established primary fibroblast cultures from a Japanese raccoon dog (Nyctereutes viverrinus) and a Japanese red fox (Vulpes vulpes japonica) and generated highly contiguous reference genome assemblies using Oxford Nanopore Technologies PromethION long-read sequencing. The Japanese raccoon dog assembly spanned 2.69 Gb in 813 scaffolds, with a scaffold N50 of 52&#xa0;Mb and a Benchmarking Universal Single-Copy Orthologs (BUSCO) completeness score of 98.2%. The Japanese red fox assembly spanned 2.47 Gb in 903 scaffolds, with a scaffold N50 of 139&#xa0;Mb and a BUSCO completeness score of 97.5%. Phylogenomic analysis placed the Japanese raccoon dog in a lineage distinct from the continental raccoon dog, supporting its evolutionary differentiation within Nyctereutes. The Japanese red fox formed a distinct lineage within the red fox clade, consistent with its recognized regional differentiation. These genome assemblies and associated fibroblast cultures provide resources for studies of canid systematics, population history, local adaptation, comparative genome evolution, and conservation genetics.

Canidae

Expanded detection of canine enteric viruses in UK dogs with diarrhoea.

Canine enteric viruses are an important cause of gastrointestinal disease in pet dogs worldwide. Routine diagnosis often relies on pathogen-specific PCR assays, which may fail to detect some viruses, particularly neglected pathogens or genetically divergent variants of established threats. This limits both clinical characterization of affected patients and broader understanding of disease ecology. To address these limitations, we applied metagenomics and a viral discovery bioinformatics pipeline to faecal samples from diarrhoeic dogs in the UK that had been submitted routinely for PCR-based diagnostic testing. Across 80 dogs, we identified 12 viruses known to infect canids, 9 of which have not previously been reported in UK dogs. Among these, several taxa with prior associations to gastrointestinal disease were identified, including canine sapovirus and canine minute virus. By contrast, for other viruses newly detected in the UK, including bufavirus and rotavirus C, clinical relevance in dogs remains unclear. Notably, an identified protoparvovirus fell within the same species as human-canine-associated parvovirus 1, a recently described lineage detected in both canine and human oropharyngeal samples. We also identified a canine parvovirus 2 strain that clustered with a predominantly wildlife-associated lineage, consistent with occasional exposure at the domestic-wildlife interface rather than established circulation in dogs. These two detections illustrate how genome-level surveillance can help prioritize viruses for targeted investigation of host range and transmission context. Overall, these data broaden the catalogue of viruses associated with diarrhoeic dogs in the UK and support periodic review of diagnostic targets informed by viral metagenomic surveillance, while highlighting the need for controlled studies to assess causality and clinical relevance.

Animals

Ancient Mitogenomes Reveal the Maternal Genetic History of East Asian Gray Wolves (Canis lupus).

The gray wolf (Canis lupus) is the only wild ancestor of dogs (Canis lupus familiaris) and serves a crucial role in understanding the highly controversial issue of dog origins. Recently, ancient DNA studies on gray wolves from different regions of the Eurasian continent have achieved significant breakthroughs, providing important clues about the dog origins. As one of the potential origin areas for dogs, East Asia has seen some research on ancient dogs; however, reports related to gray wolves remain limited. In this study, we sequenced seven new mitogenomes of ancient gray wolves from Northern China, integrating them with 497 ancient and modern canid mitogenomes from published data. Our results reveal the following: (1) East Asian gray wolves have maintained high genetic diversity from ancient times to the present; (2) multiple haplogroup A gray wolves from Northern China support the hypothesis that Northeastern Eurasia is a core region for dog origins; (3) a deep gray wolf lineage in East Asia has been identified in this study; (4) different mitogenomes concentrated at the Jinchankou site indicate that admixture may have frequently occurred in the northeastern edge of the Tibetan Plateau. These findings enhance our understanding of the maternal genetic history of gray wolves in East Asia.

Animals