Use of stable isotopes to reveal trophic relationships and transmission of a food-borne pathogen

Predators in food webs are valuable sentinel species for zoonotic and multi-host pathogens such as Toxoplasma gondii. This protozoan parasite is ubiquitous in warm-blooded vertebrates, and can have serious adverse effects in immunocompromised hosts and foetuses. In northern ecosystems, T. gondii is disproportionately prevalent in Inuit people and wildlife, in part due to multiple routes of transmission. We combined data on T. gondii infection in foxes from Nunavik (northern Québec, Canada) with stable isotope data tracking trophic relationships between foxes and several of their main prey species. Red (Vulpes vulpes) and Arctic fox (Vulpes lagopus) carcasses were collected by local trappers from 2015 to 2019. We used magnetic capture PCR to detect DNA of T. gondii in heart and brain tissues, and enzyme-linked immunosorbent assay to detect antibodies in blood. By linking infection status with diet composition, we showed that infected foxes had a higher probability of consuming aquatic prey and migratory geese, suggesting that these may be important sources of T. gondii transmission in the Arctic. This use of stable isotopes to reveal parasite transmission pathways can be applied more broadly to other foodborne pathogens, and provides evidence to assess and mitigate potential human and animal health risks associated with T. gondii in northern ecosystems.

Coexistence of two sympatric predators in a transitional ecosystem under constraining environmental conditions: a perspective from space and habitat use

BACKGROUND

Range expansion of species, a major consequence of climate changes, may alter communities substantially due to competition between expanding and native species.

METHODS

We first quantified size differences between an expanding habitat generalist, the red fox (Vulpes vulpes), and a circumpolar habitat specialist, the Arctic foxes (Vulpes lagopus), at the edge of the Arctic, where climate-related changes occur rapidly, to predict the likelihood of the larger competitor escalating interference to intraguild killing. We then used satellite telemetry to evaluate competition in a heterogeneous landscape by examining space use early during the foxes' reproductive period, when resource scarcity, increased-food requirements and spatial constraints likely exacerbate the potential for interference. We used time-LoCoH to quantify space and habitat use, and Minta's index to quantify spatio-temporal interactions between neighbors.

RESULTS

Our morphometric comparison involving 236 foxes found that the potential for escalated interference between these species was high due to intermediate size difference. However, our results from 17 collared foxes suggested that expanding and native competitors may coexist when expanding species occur at low densities. Low home-range overlap between neighbors suggested territoriality and substantial exploitation competition for space. No obvious differential use of areas shared by heterospecific neighbors suggested low interference. If anything, intraspecific competition between red foxes may be stronger than interspecific competition. Red and Arctic foxes used habitat differentially, with near-exclusive use of forest patches by red foxes and marine habitats by Arctic foxes.

CONCLUSION

Heterogeneous landscapes may relax interspecific competition between expanding and native species, allowing exclusive use of some resources. Furthermore, the scarcity of habitats favored by expanding species may emphasize intraspecific competition between newcomers over interspecific competition, thus creating the potential for self-limitation of expanding populations. Dominant expanding competitors may benefit from interference, but usually lack adaptations to abiotic conditions at their expansion front, favoring rear-edge subordinate species in exploitation competition. However, due to ongoing climate change, systems are usually not at equilibrium. A spread of habitats and resources favorable to expanding species may promote higher densities of antagonistically dominant newcomers, which may lead to extirpation of native species.

Giardia and Cryptosporidium in resident wildlife species in Arctic Alaska

Giardia and Cryptosporidium are zoonotic protozoan parasites that can infect humans and other taxa, including wildlife, often causing gastrointestinal illness. Both have been identified as One Health priorities in the Arctic, where climate change is expected to influence the distribution of many wildlife and zoonotic diseases, but little is known about their prevalence in local wildlife. To help fill information gaps, we collected fecal samples from four wildlife species that occur seasonally on the northern Alaska coastline or in nearshore marine waters-Arctic fox (Vulpes lagopus), polar bear (Ursus maritimus), Pacific walrus (Odobenus rosmarus divergens), and caribou (Rangifer tarandus)-and used immunofluorescence assays to screen for Giardia cysts and Cryptosporidium oocysts. We detected Giardia cysts in 18.3% and Cryptosporidium oocysts in 16.5% of Arctic foxes (n = 109), suggesting that foxes may be potentially important hosts in this region. We also detected Giardia cysts in a single polar bear (12.5%; n = 8), which to our knowledge represents the first such report for this species. Neither parasite was detected in walruses or caribou.

Dental and temporomandibular joint pathology of the Arctic fox (Vulpeslagopus)

Museum skull specimens from 224 Arctic foxes (Vulpes lagopus) were examined macroscopically using an established protocol for examination of mammalian skull specimens. Foxes were collected from coastal and island regions of Alaska, USA, except for two individuals. Collection years ranged from 1931 to 2016 with most specimens collected during the 1950s and 1960s. The study population comprised more females (n = 134, 59.8%) than males (n = 83, 37.0%) and individuals of unknown sex (n = 7, 3.1%). There were 108 (48.2%) young adults, 115 (51.3%) adults, and one (0.4%) individual of unknown age. A total of 8,891 teeth (94.5%) were available for examination. The most common types of pathology observed were periodontitis (n = 222, 99.1%), dental fractures (n = 175, 78.1%) and attrition/abrasion (n = 198, 88.4%). Periapical lesions (n = 12, 5.3%), temporomandibular joint (TMJ) osteoarthritis (n = 3, 1.3%) and root number variation (n = 5, 2.2%) were less common. Enamel hypoplasia was noted in eight foxes (3.6%), all of which were discovered on St. Matthew Island, Alaska, in 1963. As in other canid species, periodontitis, attrition/abrasion and tooth fractures are common in the Arctic fox, while TMJ pathology is rare. Loss of tooth crown substance probably reflects the influence of diet, interspecific and conspecific aggression and oral trauma due to trapping and hunting methods. The high prevalence of periodontitis is probably also due to the combined effects of diet, genetics and host immune reaction to oral bacteria.

Plastic and other anthropogenic debris in Arctic fox (Vulpes lagopus) faeces from Iceland

Anthropogenic debris, including plastic pollution, is a growing concern in the Arctic and negatively impacts both marine and coastal organisms. The aim of this study was to investigate the potential for using Arctic fox (Vulpes lagopus) faeces as a monitoring tool for plastic pollution in the Arctic environment. Arctic fox faeces were collected in different regions of Iceland and analysed for anthropogenic debris presence larger than 300 µm, and diet composition. In total, 235 faecal samples from 1999, 2017, 2018 and 2020 were analysed. The overall frequency of occurrence of plastic and other anthropogenic material was 5.11% and was found in samples across all regions and years. There were no statistical differences in anthropogenic debris ingested, depending on year or region. There were no obvious differences in diet composition between samples that contained anthropogenic debris and samples without. The suitability of Arctic fox faeces as a method to monitor plastic and anthropogenic debris levels in the Arctic environment remains debatable: Whilst the vast distribution range of the Arctic fox and the non-invasive collection methodology of faecal samples could be utilised as a good monitoring tool, the overall low uptake and unclear source of plastic and anthropogenic debris (marine or terrestrial) makes the interpretation of the data difficult. Nevertheless, debris ingestion by Arctic foxes remains a concern and warrants further studies.

Changes in dental wear and breakage in arctic foxes across space and time: Evidence for anthropogenic food subsidies?

Increased human presence in the Arctic may affect its vulnerable ecosystems. Effects on arctic and red foxes provide notable examples. Both have been documented to take anthropogenic subsidies when available, which can change diet and ranging patterns in complex ways that can either benefit or harm populations, depending on the situation. Understanding this complexity requires new tools to study impacts of increasing human presence on endemic mammals at high latitudes. We propose that dental ecology, specifically tooth wear and breakage, can offer important clues. Based on samples of arctic foxes (Vulpes lagopus Linnaeus, 1758) trapped prior to (n = 78) and following (n = 57) rapidly growing human presence on the Yamal Peninsula, Russia, we found that foxes trapped recently in proximity to human settlement had significantly less tooth wear and breakage. This is likely explained by a dietary shift from consumption of reindeer carcasses (Rangifer tarandus Linnaeus, 1758) including bone to softer human-derived foods, especially when preferred smaller prey (e.g., West Siberian lemmings, Lemmus sibiricus Kerr, 1792 and arctic lemmings, Dicrostonyx torquatus Pallas, 1778) are unavailable. These results suggest that tooth wear can be a useful indicator of the consumption of anthropogenic foods in arctic foxes.

Diet reveals potential for competition and coexistence among coyotes (Canis latrans), red foxes (Vulpes vulpes), and gray foxes (Urocyon cinereoargenteus)

Species can alleviate competition by reducing diet overlap. Non-native coyotes (Canis latrans Say, 1823) and historically native gray foxes (Urocyon cinereoargenteus (Schreber, 1775)) have expanded their ranges and may compete with native red foxes (Vulpes vulpes (Linnaeus, 1758)). To examine potential competition among canids in Maine, USA, we compared δ13C and δ15N from muscle and hair samples to assess relative resource use, and we compared frequency of occurrence of prey items from stomach contents to assess diets. For these species, red foxes consumed anthropogenically based foods the most in fall and early winter, gray foxes consumed anthropogenically based foods the most in summer, and coyotes consumed anthropogenically based foods the least in all seasons. Coyotes held the highest relative trophic position in fall and early winter, red foxes held the highest relative trophic position in summer, and gray foxes held the lowest relative trophic position. Based on stomach contents, gray foxes had the broadest diet and consumed the most plants, and coyotes had the narrowest diet. Red foxes were the only species to show isotopic niche overlap with both potential competitors across seasons. Thus, they may be most susceptible to competitive exclusion among these canids, with implications for community dynamics as ranges shift due to human activity.

Domestic cats as environmental lead sentinels in low-income populations: a One Health pilot study sampling the fur of animals presented to a high-volume spay/neuter clinic

Non-human animals serve as sentinels for numerous issues affecting humans, including exposure to toxic heavy metals like lead. Lead plays a role in perpetuating cycles of poverty in low-income communities due to the inequitable distributions of indoor health risks from lower-quality housing and outdoor health risks from industry and polluters, compounded by inequitable distributions of heath care and education. In this pilot study, we explore the potential for studying lead in low-income populations by partnering with nonprofit veterinary outreach programs. We investigate the lead concentration in fur samples of 85 domestic cats (Felis catus) presented to a high-volume spay/neuter clinic and report a mean of 0.723 μg of lead per gram of fur. This study reveals new information about lead exposure in cats in the USA, including that females had greater lead exposure than males, lead exposure increased with increasing amount of access to the outdoors, and lead exposure increased in cats with decreased body condition. We propose that pet, feral, and free-roaming cats presented to high-volume spay/neuter clinics could serve as a source of data about lead exposure in disadvantaged communities where these clinics already operate. Such a non-invasive surveillance system using inert, unobtrusively obtained samples could be deployed to detect highly exposed cats, prompting to follow up contact to a cat's caretakers to recommend seeking lead testing for themselves, their families, and their neighbors.

Individual dietary specialization in a generalist predator: A stable isotope analysis of urban and rural red foxes

Some carnivores are known to survive well in urban habitats, yet the underlying behavioral tactics are poorly understood. One likely explanation for the success in urban habitats might be that carnivores are generalist consumers. However, urban populations of carnivores could as well consist of specialist feeders. Here, we compared the isotopic specialization of red foxes in urban and rural environments, using both a population and an individual level perspective. We measured stable isotope ratios in increments of red fox whiskers and potential food sources. Our results reveal that red foxes have a broad isotopic dietary niche and a large variation in resource use. Despite this large variation, we found significant differences between the variance of the urban and rural population for δ13C as well as δ15N values, suggesting a habitat-specific foraging behavior. Although urban regions are more heterogeneous regarding land cover (based on the Shannon index) than rural regions, the dietary range of urban foxes was smaller compared with that of rural conspecifics. Moreover, the higher δ13C values and lower δ15N values of urban foxes suggest a relatively high input of anthropogenic food sources. The diet of most individuals remained largely constant over a longer period. The low intraindividual variability of urban and rural red foxes suggests a relatively constant proportion of food items consumed by individuals. Urban and rural foxes utilized a small proportion of the potentially available isotopic dietary niche as indicated by the low within-individual variation compared to the between-individual variation. We conclude that generalist fox populations consist of individual food specialists in urban and rural populations at least over those periods covered by our study.

Dietary variation in Icelandic arctic fox (Vulpes lagopus) over a period of 30 years assessed through stable isotopes

Identifying resources driving long-term trends in predators is important to understand ecosystem changes and to manage populations in the context of conservation or control. The arctic fox population in Iceland has increased steadily over a period of 30 years, an increase that has been attributed to an overall increase in food abundance. We hypothesized that increasing populations of geese or seabirds were driving this growth. We analyzed stable isotopes in a long-term series of collagen samples to determine the role of these different resources. The isotopic signatures of arctic foxes differed consistently between coastal and inland habitats. While δ¹⁵N displayed a non-linear change over time with a slight increase in the first part of the period followed by a decline in both habitats, δ¹³C was stable. Stable isotope mixing models suggested that marine resources and rock ptarmigan were the most important dietary sources, with marine resources dominating in coastal habitats and rock ptarmigan being more important inland. Our results suggest that seabirds may have been driving the arctic fox population increase. The rapidly increasing populations of breeding geese seem to have played a minor role in arctic fox population growth, as rock ptarmigan was the most important terrestrial resource despite a considerable decrease in their abundance during recent decades. This study shows that a long-term population trend in a generalist predator may have occurred without a pronounced change in main dietary resources, despite ongoing structural changes in the food web, where one species of herbivorous birds increased and another decreased.