Didelphis Virginiana Research Articles

3D hyoid and tongue kinematics reveal mechanism of tongue base retraction during swallowing in Didelphis virginiana

In anthropoid primates, tongue base retraction (TBR) is a key event for airway protection and bolus propulsion during swallowing. In macaques, hyoid protraction and elevation during swallowing reduce the oral volume and squeeze the tongue base to retract. This novel hyoid-powered hydraulic TBR mechanism implies that the morphology and position of the hyoid are functionally relevant for TBR performance. However, macaque’s highly derived craniofacial and hyoid morphology precludes inference on the evolutionary history and driving mechanism of TBR across mammal phylogeny at large. Here we use biplanar videoradiography and the XROMM workflow to infer TBR mechanism in Didelphis virginiana through high-resolution 3D hyolingual kinematics. Similar to macaques, Didelphis has an incomplete hyoid cornu, which would enable a large hyoid range of motion that facilitates oral volume reduction. Unlike macaques, Didelphis hyoid has a more posteriorly resting hyoid position. We predict that TBR will occur in Didelphis through a similar hyoid-powered hydraulic mechanism. We find Didelphis deploys TBR during the first opening (O1) phase (liquid) or slow-open phase (solid) of jaw cycle with retraction and elevation of midline posterior tongue markers. Minimal retraction occurs in lateral tongue markers where extrinsic lingual muscles insert. The tongue base and posterior tongue are lengthening, narrowing and increasing in height during TBR, consistent with predictions based on muscular hydrostat model. The tongue base was not isovolumetric during TBR, but the volume change was orders of magnitude smaller than that observed in macaques. Hyoid protraction and elevation occur before and continue throughout TBR, which strongly suggest concurrent reduction of oral volume as well. Our preliminary data suggest the TBR mechanism in opossums may differ in important ways from that utilized by macaques, where opossums could employ a combination of hydrostatic deformation and hydraulic mechanism to drive retraction of tongue base. We provide novel insights into the conservation of TBR across therian mammals and extend our understanding on the form-function relationships between the hyolingual apparatus and swallowing biomechanics. Hinds Fund, University of Chicago This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Assessment of habitat‐specific competition for oral rabies vaccine baits between raccoons and opossums

AbstractThroughout the eastern United States, the National Rabies Management Program (NRMP) distributes oral rabies vaccine (ORV) baits to manage rabies virus circulation in raccoon (Procyon lotor) populations. The consumption of vaccine baits by non‐target species including Virginia opossums (Didelphis virginiana) may reduce the effectiveness of ORV programs, but competition for baits remains poorly quantified in many areas of the southeastern United States. We distributed placebo ORV baits injected with a biomarker across 4 land cover types (bottomland hardwood, upland pine, riparian, isolated wetland) on the Savannah River Site in South Carolina, USA, 2017–2019. We then trapped and collected whiskers from 247 raccoons and 78 opossums to assess biomarker presence using fluorescent microscopy. Our data revealed greater bait uptake probability by raccoons (estimated x̅ = 0.30, 95% CI = 0.19–0.44) compared to opossums (estimated x̅ = 0.11, 95% CI = 0.05–0.23) across all cover types surveyed. Probability of bait consumption was not affected by cover type or the abundance of raccoons or opossums. Among raccoons, males were more likely to consume baits than females (estimated x̅ = 0.28, 95% CI = 0.17–0.44 for males and 0.14, 95% CI = 0.05–0.31 for females) and probability of consumption increased by 0.08 with each additional day trapped during the 10‐day trapping session. Uptake rates for raccoons were relatively low compared to other studies and not influenced by competition with opossums. These low consumption rates indicate that additional research addressing the roles of baiting season, bait density, and resource selection will be important to maximize ORV bait uptake by target species in these southeastern landscapes.

Using blood lead concentrations of wildlife sentinels to identify environmental risk factors of lead exposure for public health and wildlife rehabilitation efforts.

Lead poisoning remains a persistent health issue for both humans and wildlife, despite strides to reduce lead contamination in the environment. Using Geographic Information Systems (GIS), this study explores the associations between blood lead levels (BLLs) in wildlife sentinels and possible built environment lead exposure risk factors in the Minneapolis-Saint Paul, Minnesota urban area. Results show a high-level of heterogeneity in animal BLLs (n = 472) across our urban environment and suggest that each kilometer increase in road density is associated with a 17.07% (95% CI: 1.48%, 35.05%) increase in BLL in our study species of Virginia opossums and Eastern gray squirrels, and a 14.28% (95% CI: 1.16%, 29.09%) increase in BLL of rock pigeons. For squirrels and opossums, we see an additional 5.72% (95% CI: 0.59%, 10.85%) increased risk of BLL for every 1000 people per square-mile. The relationship between animal sentinels and environmental hazards can give us an insight into the potential lead exposure risks for humans. The use of wildlife sentinel data to explore environmental risk factors supports a One Health approach to better address public health questions and aid in wildlife rehabilitation related to residual lead poisoning from ambient environmental exposures.

Collection of triatomines from sylvatic habitats by a Trypanosoma cruzi-infected scent detection dog in Texas, USA.

Triatomine insects, vectors of the etiologic agent of Chagas disease (Trypanosoma cruzi), are challenging to locate in sylvatic habitats. Collection techniques used in the United States often rely on methods to intercept seasonally dispersing adults or on community scientists' encounters. Neither method is suited for detecting nest habitats likely to harbor triatomines, which is important for vector surveillance and control. Furthermore, manual inspection of suspected harborages is difficult and unlikely to reveal novel locations and host associations. Similar to a team that used a trained dog to detect sylvatic triatomines in Paraguay, we worked with a trained scent detection dog to detect triatomines in sylvatic locations across Texas. Ziza, a 3-year-old German Shorthaired Pointer previously naturally infected with T. cruzi, was trained to detect triatomines. Over the course of 6 weeks in the fall of 2017, the dog and her handler searched at 17 sites across Texas. The dog detected 60 triatomines at 6 sites; an additional 50 triatomines were contemporaneously collected at 1 of these sites and 2 additional sites without the assistance of the dog. Approximately 0.98 triatomines per hour were found when only humans were conducting searches; when working with the dog, approximately 1.71 triatomines per hour were found. In total, 3 adults and 107 nymphs of four species (Triatoma gerstaeckeri, Triatoma protracta, Triatoma sanguisuga, and Triatoma indictiva) were collected. PCR testing of a subset revealed T. cruzi infection, including DTUs TcI and TcIV, in 27% of nymphs (n = 103) and 66% of adults (n = 3). Bloodmeal analysis of a subset of triatomines (n = 5) revealed feeding on Virginia opossum (Didelphis virginiana), Southern plains woodrat (Neotoma micropus), and eastern cottontail (Sylvilagus floridanus). A trained scent detection dog enhanced triatomine detections in sylvatic habitats. This approach is effective at detecting nidicolous triatomines. Control of sylvatic sources of triatomines is challenging, but this new knowledge of specific sylvatic habitats and key hosts may reveal opportunities for novel vector control methods to block the transmission of T. cruzi to humans and domestic animals.

Predation risk in tree squirrels: implications of the presence of free‐ranging dogs

AbstractSmall mammals show variations in activity patterns due to the use of resources and the risk of predation. However, in the case of tree squirrel species, the factors that affect their activity patterns are poorly studied. We used camera trapping to investigate the activity patterns of three different squirrel species of the genus Sciurus, two species of squirrel (Sciurus aureogaster and S. oculatus) from Mexico and one from the Iberian Peninsula (S. vulgaris). In addition, we compared their activity patterns with the potential predator community and their most important predators (Mexico: gray fox Urocyon cinereoargenteus, ringtail Bassariscus astutus, Opossum Didelphis virginiana; Spain: red fox Vulpes vulpes, pine and stone marten Martes spp.), and with feral and free‐ranging dogs (Canis lupus familiaris). We evaluated the predation risk by the carnivore community on the squirrels when they descend to the ground by studying their temporal overlap and observing if the squirrels have different activity patterns adjusted to the carnivore community in each study area. The results showed that the three species of squirrels consistently descended to the ground during the day, showing a variable maximum peak of activity between 8:00 and 12:00 h. Temporal overlap of activity patterns of the three species with the carnivore community was low (Δ = 0.12–0.36), same as with the main predators (Mexico: gray fox Δ = 0.14–0.21, ringtail Δ = 0.08–0.09, opossum Δ = 0.06–0.07; Spain: red fox Δ = 0.39, martens Δ = 0.22). However, temporal overlap of activity patterns with the domestic dog was moderate‐high in the three squirrel species (Mexico Δ = 0.55–0.88, Spain Δ = 0.79). These results show that the species of the genus Sciurus have adjusted their activity patterns of ground use to reduce predation risk by wild predators but not with feral and free‐ranging dogs, something which can pose a serious conservation problem for these species.

Effects of landscape cover and yard features on feral and free-roaming cat (Felis catus) distribution, abundance and activity patterns in a suburban area

Abstract Feral and free-roaming domestic cats (Felis catus) are invasive predators throughout the world. In some areas, cats occur in higher densities than native mammalian predators and can have severe effects upon prey populations. We set 48 wildlife game cameras in residential yards in Arkansas, USA, to evaluate which landscape and yard features influenced cat abundance occurring in yards. In addition, we quantified the daily activity patterns of free-roaming cats and explored how habitat features or predator activity influenced the timing of cat activity. We found that cats were present in 70.8% of yards with an average of three recognizable individuals per yard. Abundance of cats was higher than all native mesopredators except for raccoon (Procyon lotor) and Virginia opossum (Didelphis virginiana). Cat abundance and minimum population decreased when forest cover was high within 400 m of the camera. Cats were active at all times of the day but tended to be more diurnal in areas closer to city centers or in agricultural settings. Conversely, cats were more nocturnal later in the summer and in areas that had high levels of predator activity. Our results indicate that cats are widespread in this region and their relative abundance is driven more by landscape features than by yard features, possibly due to their large home ranges. Cats may alter their activity to better coexist with predators. Alteration in yard features is unlikely to be an effective deterrent for cats and more direct control measures may be necessary.

Evaluating anthropogenic influence on a mesopredator: opossum (Didelphis virginiana) isotope values influenced by corn agriculture more than urbanization

The composition of North American communities is changing due to anthropogenic land-use alteration. Mammalian mesopredators’ ability to consume anthropogenic trash due to their generalist diet has been referenced to partially explain their success in altered landscapes as they spread northward. We evaluated this assumption using carbon isotope values (δ13C) of the Virginia opossum ( Didelphis virginiana (Kerr, 1792)), a mesopredator expanding its range. δ13C values increase from consumption of C4 plants, including corn, a common food additive in North America. Opossum hairs from the Midwestern U.S. and Northeast were evaluated using generalized linear mixed models (GLMMs) to compare the predictive performances between winter harshness variables and anthropogenic variables. We also evaluated δ13C values through time to test if the temporal pattern of increased corn additives is mirrored in northern opossums. The best-performing GLMM included year and percentage corn fields as positive covariates. Variance in δ13C values increased exclusively in the “cornbelt” Midwest after 1970. δ13C values compared across space and time bolster evidence for the influence of agricultural development on the opossum’s range expansion.

Effects of sardines as an attractant on carnivore detection and temporal activity patterns at remote camera traps

Context Adding an attractant to remote camera traps has become a popular method to increase detections of cryptic carnivores. However, there is ongoing debate about whether this practice can bias the behaviour and activity patterns of these species. Aims Our aim was to determine how using a popular attractant at camera traps could affect carnivore detection probabilities and temporal activity. Methods We used an experimental design in which we randomly set half of our camera traps on arrays at two sites in western North Carolina with an attractant: canned sardines in oil. Halfway through the survey season, we switched which camera traps had sardines and which did not. We estimated detection probability for each carnivore species observed using occupancy models, and we used kernel density estimations to evaluate changes in diel activity patterns between camera traps with and without an attractant. Key results We found that when sardines were used at camera traps, detectability of bobcats (Lynx rufus), coyotes (Canis latrans), northern raccoons (Procyon lotor), Virginia opossums (Didelphis virginiana), and eastern spotted skunks (Spilogale putorius) more than doubled, but there was little or no effect on striped skunk (Mephitis mephitis) detectability. Of the species we most frequently detected (coyotes, raccoons, and opossums), activity patterns between camera traps with and without a sardine attractant overlapped moderately to highly, and a significant effect on diel activity patterns was observed only for raccoons. Conclusions Use of attractants can greatly increase the probability of detecting nearly all carnivores at camera traps. The effects of attractants on diel activity patterns are species-specific, with two of our three most-detected species unaffected by their use, suggesting that attractants can be used to effectively study these behaviours in some carnivore species. Implications A sardine attractant can increase the detection of many carnivore species, using camera traps, without causing a significant deviation of diel activity patterns, thus allowing for unbiased investigations into most species’ spatio–temporal behaviour in the Appalachian Mountains – and likely other systems.

Effects of multiple aspects of anthropogenic landscape change on mesopredator relative abundance

Context Anthropogenic landscape changes have substantial effects on biodiversity and animal populations worldwide. However, anthropogenic landscape change can take a variety of forms, and its effects on wildlife species can vary by landscape context and scale. It is therefore critical that studies of the effects of anthropogenic landscape change on wildlife consider landscape context and model effects of landscape change at multiple scales. Mesopredators serve as an excellent case study of scale-dependent and even contradictory effects of anthropogenic landscape change, because mesopredator populations can respond both positively and negatively to landscape change depending on its form (e.g. agricultural production, urbanisation) and scale. Aims The aim of this study was to model relationships between multiple aspects of anthropogenic landscape change, including agricultural production and the proliferation of non-native shrubs, and relative abundance of three mesopredator species: Virginia opossum (Didelphis virginiana), striped skunk (Mephitis mephitis), and raccoon (Procyon lotor). Methods We summarised landscape variables at two scales and built both single-scale and multi-scale models linking relative abundance of mesopredators to landscape variables. Key results We found that relative abundance of all three species was most related to either the transition from natural areas to agricultural areas (brown-to-green gradient) or the likelihood of presence of non-native shrubs. We also found that responses to anthropogenic landscape change varied by spatial scale; for instance, skunks and raccoons had higher relative abundance in parts of Illinois with more forest cover and agriculture, respectively, but avoided more highly forested and agricultural areas, respectively, at smaller scales. Conclusions Mesopredator responses to landscape change were highly variable and scale-dependent, but were generally related to transitions from forest to agriculture or the presence of non-native shrubs. Implications Our study demonstrates the need to model effects of anthropogenic landscape change at multiple scales, given the differing results that can be achieved when landscape variables are measured at multiple scales.

Patologia de metazoários e protozoários em gambás selvagens (Didelphis Virginiana) no México

ABSTRACT: The aim was to describe the incidence and lesions caused by metazoan and protozoan parasites in Didelphis virginiana opossums in Mexico. From 2019 to 2021, twenty D. virginiana were collected from the state of Colima, Mexico. Post mortem, parasitological, and histopathological studies were performed to identify and describe their lesions and findings. All opossums(20/20) presented at least one type of parasite of the twelve found; the most abundant were nematodes 58.33% (7/12) Didelphostrongylus hayesi, Turgida turgida, Cruzia sp., Viannaia sp., Trichuris didelphis, Trichostrongylidae and Gnathostoma sp. Protozoa 25% (3/12), including Sarcocystis sp., Besnoitia sp., and Sarcocystis sp. A single specimen of Mathevotaenia sp., 8.3% (1/12), and Paragonimus mexicanus 8.3%, were identified (1/12). The most affected systems were the digestive, respiratory, and musculoskeletal. The most abundant parasites were Turgida turgida (20/20) 100%, Cruzia sp., (16/20) 80%, and Viannaia sp. (6/20) 30%, followed by Sarcocystis sp. cysts, (6/20) 30%. The associated parasitic lesions were: D. hayesi produce eosinophilic granulomatous bronchopneumonia, P. mexicanus eosinophilic focal granulomatous pneumonia, and Besnoitia sp., focal eosinophilic lymphoplasmacytic interstitial pneumonia. Gnathostoma and T. turgida caused severe eosinophilic granulomatous focal gastritis. Viannaia sp., Sarcocystis sp., Mathevotaenia sp., and Trichostrongylidae; caused diffuse eosinophilic mucosal enteritis. Cruzia sp., and T. didelphis, induced diffuse eosinophilic mucosal typhlitis. Sarcocystis sp. cysts were detected in the cytoplasm of muscle fibers without histological changes.

Mammals of Hazeldell Nature Preserve, Pulaski County, Kentucky: A Rare Highland Rim Ecosystem

Hazeldell Nature Preserve is a rare ecosystem on the Highland Rim of south-central Kentucky. It is the only state-protected site of its kind. This preserve is comprised of two distinct plant communities, including wet flatwoods and wet meadow. Despite its uniqueness, no ecological studies have been conducted on mammals in the past. Currently, two separate studies are underway on mammals. Here we present the results from the first of these that used camera traps set in the wet flatwoods community from 1 February to 28 March 2020. A total of 34,071 photos were taken with 553 having images of 12 species of mammals. The four most photographed species were eastern gray squirrel, Virginia opossum, white-footed deermouse, and white-tailed deer. These four species appeared in 91% of photos. The remaining 49 photos were of eight species including: eastern cottontail, coyote, bobcat, northern raccoon, striped skunk, southern flying squirrel, common gray fox, and eastern fox squirrel. Woodchuck and eastern chipmunk were not photographed during the study, yet each have ranges that include the preserve. These burrowers may avoid the preserve because of the secondary water table and saturated soil that occur during extended periods. The results of this study serve as baseline data for comparison to future camera trapping. Continued photo documentation will be used to identify changes in the mammal species composition of the preserve caused by species range changes in response to various factors, including habitat fragmentation and climate change.

Identification of the parasite, Trypanosoma cruzi, in multiple tissues of epidemiological significance in the Virginia opossum (Didelphis virginiana): Implications for environmental and vertical transmission routes.

Trypanosoma cruzi, a parasitic protozoan, is endemic to the Americas and the causative agent of Chagas disease in humans. In South America, opossums facilitate transmission via infected anal gland secretions in addition to transmission via triatomine vectors. In North America, the Virginia opossum is a reservoir host for the parasite with transmission routes that are not clearly defined. The unique biology of this marsupial provides the opportunity to investigate vertical transmission in this wildlife species in situ. Our objectives were to investigate alternative routes of transmission that may facilitate spillover into other species and to determine if vertical transmission was evident. Virginia opossums were sampled at 10 trapping locations over a 10-month period in a 5-county region of north central Florida. Peripheral blood, fecal swabs, and anal gland secretions were collected from each adult individual, and peripheral blood was collected from joey opossums. Total DNA was extracted from each collected sample type, and T. cruzi infected individuals and the infecting Discrete Typing Unit (DTU) were identified using real time PCR methods. Adult Virginia opossums (n = 112) were infected with T. cruzi (51.8%, 95% CI [42.6-60.8%]) throughout the sampled period and at each location. T. cruzi DNA was found in each of the three biological sample types. Vertical transmission of T. cruzi was inferred in one litter of mother-dependent (n = 20, 5.0%, 95% CI [0.9-23.6%]) joey opossums where 2 joeys from this same litter were rtPCR positive for T. cruzi. We inferred vertical transmission from mother to neonate which may serve to amplify the prevalence of T. cruzi in adult Virginia opossums. T. cruzi DNA was detected in the anal gland secretions of Virginia opossums. Infected anal gland secretions suggest a possible environmental route of transmission for T. cruzi via the deposition of contaminated feces and spraint at wildlife latrines. Only DTU1 was identified in the sampled population which is consistent with human autochthonous cases in the United States.

Biofluorescence in the masked palm civet (Paguma larvata)

Biofluorescence has come to general public attention over the last decade with the industrial production of “black lights”. While numerous reports on biofluorescence have become available for some groups of species such as invertebrates, birds, amphibians, and reptiles, there are fewer reports on fluorescence in mammals. So far, ultraviolet fluorescence is known from a few mammal species only, including flying squirrels, mice, Chinese pangolins, Virginia opossums and other didelphid marsupials, springhares, African pygmy hedgehogs, European hedgehogs, and platypuses. The fluorescence is, however, not produced by the animal itself in the case of hedgehogs, but by commensal bacteria. Green fluorescence can also be expressed by transgenic animals, including non-human primates, and the trait can become inheritable.

Confirmation of the presence of Rickettsia felis infecting Ornithodoros puertoricensis in Mexico.

Soft ticks are neglected competent vectors of a wide range of pathogenic microorganisms, among which bacteria of the genera Rickettsia and Borrelia stand out. In Mexico, previous studies have shown the presence of a member of the Ornithodoros talaje complex in the Virginia opossum (Didelphis virginiana Didelphimorphia: Didelphidae Kerr) from southeastern Mexico. However, its specific identification has not been achieved. Two D. virginiana were treated in a private clinic during the period of April-May 2022. Tick larvae were manually removed, DNA extraction was performed, and some genes from various bacterial and parasitic pathogens were amplified and sequenced. A total of 96 larvae were recovered, which were morphologically identified as Ornithodoros puertoricensis (Ixodida: Argasidae Fox); the 16 S sequences showed a similarity of 96.79%-99.51% with sequences of O. puertoricensis from Panama and Colombia. The presence of Rickettsia felis (Rickettsiales: Rickettsiaceae Bouyer et al.) was detected in 15 specimens from one host. The soft tick O. puertoricensis is recorded for the first time as an ectoparasite of the Virginia opossum in America and represents the second report for this soft tick in Mexico since 1963. This represents the most northern record of this tick species in its geographic distribution and brings a new soft tick-Rickettsia association.

An urban cast of characters: Landscape use and cover influencing mammal occupancy in an American midwestern city

With future human population growth concentrating in urban areas, cities are working to counterbalance ecological disturbances resulting from development by incorporating green space that supports greater biodiversity. An initial line of inquiry into designing wildlife-inclusive green space involves evaluating landscapes that are associated with the habitat use of urban species. In this study, we utilized occupancy modeling to estimate select terrestrial mammal presence in a fast-growing mid-sized midwestern city to determine possible taxa-specific associations with multiple land use and cover variables, specifically those associated with higher degrees of human activity. Using motion-triggered infrared trail cameras over eight seasons from winter 2017 to fall 2018, we applied a single-species, single-season stacked design to estimate occupancy for eight urban dwelling mammals. Taxa-specific models contained one of three possible detection variables (null, percent green space, or percent impervious surface) and combinations of three species-specific variables, natural and anthropogenic. We hypothesized that large species, coyote (Canis latrans) and white-tailed deer (Odocoileus virginianus), would exhibit the most positive association to natural land cover and the most negative association to anthropogenic land cover. We also hypothesized that small and medium sized species, eastern cottontail (Sylvilagus floridanus), gray squirrel (Sciurus carolinensis), opossum (Didelphis virginiana), raccoon (Procyon lotor), red fox (Vulpes vulpes), and striped skunk (Mephitis mephitis), would demonstrate a neutral association to land cover type, anthropogenic or natural. Our results indicated that the presence of anthropogenic features rather than any particular natural land cover may be driving wildlife distribution in our study area, as none of our species demonstrated a positive association to natural land cover (percent recreation, residential yards, vacant land, or woodland). Species with a wide range of body sizes, showed a negative association with residential yards, indicating that this type of green space may be an unnecessary or unsuitable subsidizing resource in our study area. With our results in mind, we recommend increasing the amount of natural or less manicured green space to offset the intensity of impervious surface as well as encouraging the establishment of native vegetation in existing and newly constructed residential development to better connect urban green space and residential yards to larger adjoining tracts of natural landscapes. For our study area and other cities in similar phases of development, these suggestions may be essential first steps to reduce biodiversity loss and strengthen community ecology as urban areas continue to grow.

Experimental Rickettsia typhi Infection in Monodelphis domestica: Implications for Opossums as an Amplifying Host in the Suburban Cycle of Murine Typhus.

Murine typhus is an acute undifferentiated febrile illness caused by Rickettsia typhi. In the United States, its reemergence appears to be driven by a shift from the classic rat-rat flea cycle of transmission to one involving opossums (Didelphis virginiana) and cat fleas. Little is known of the ability of opossums to act as a reservoir and amplifying host for R. typhi. Here, we use Monodelphis domestica (the laboratory opossum) as a surrogate for D. virginiana. Opossums were inoculated via the intraperitoneal (IP) or intradermal (ID) route with 1 × 106 viable R. typhi. Blood and tissues were collected on days 6, 13, 20, and 27 or if moribund. Although one ID-infected opossum died, the remainder did not appear ill, whereas half of the IP-inoculated animals succumbed to infection. Rickettsemia was demonstrated in all animals through week 2 of infection and sporadically in weeks 3 and 4. Rickettsia typhi DNA was detected in all tissues, with most animals demonstrating the presence of bacteria into weeks 3 and 4. Histopathology and immunohistochemistry demonstrated typical findings of rickettsial infection. Akin to infection in rats, the demonstration of disseminated infection, typical inflammation, and prolonged rickettsemia with relatively few clinical effects (especially in the more natural route of ID inoculation) supports the potential of opossums to act as a competent mammalian reservoir and component of the zoonotic maintenance cycle of R. typhi. Understanding the dynamics of infection within opossums may have implications for the prevention and control of murine typhus.

Dietary Patterns Suggest West Virginia Bobcats Are Generalist Carnivores

Abstract The proportion and diversity of prey species consumed by bobcats Lynx rufus are often correlated with prey abundances, individual skill level, environmental conditions, and habitat quality. Bobcats generally consume prey species that rely on mast—the fruits of trees—for basic life-history requirements. In West Virginia forests, many mast-producing tree species have declined over the past 40 y, yet the last known study on bobcat diet in the state was in 1977. Thus, we need current data to understand the effects of forest compositional changes on bobcat dietary patterns. We evaluated stomach contents of 300 bobcats collected over the 2014–2015 (n = 150) and 2015–2016 (n = 150) hunting and trapping seasons in West Virginia. Simpson's index of diversity indicated an 87% probability that two randomly selected prey items belong to different species, supporting the idea of bobcats as generalist carnivores. White-tailed deer (hereafter deer) Odocoileus virginianus (32%), mice and rats (families Cricetidae, Dipodidae, and Muridae; 30.7%), rabbits (family Leporidae; 21.3%), Virginia opossum Didelphis virginiana (18.7%), and squirrels (family Sciuridae; 17.3%) occurred most frequently. We found 92% dietary overlap between sexes and 35% between stage classes. Deer, opossum, and raccoon Procyon lotor occurred more frequently in males, whereas rabbits occurred more frequently in females. Deer occurred more frequently in adults; raccoons in yearlings; and mice and rats in juveniles. Overall occurrence of deer (−17.1%), rodents (order Rodentia; −9.5%), opossum (+13.5%), and raccoon (+5.1%) differed significantly between the 1977 study and this study, which may allude to changes in the abundance of mast-dependent prey species over time. Similarly, hard mast (i.e., nuts) production had a significant interaction effect with study season on the overall occurrence of squirrels in bobcat diets. By improving our understanding of bobcat trophic interactions, we can better manage their populations and ecological communities by managing for the dietary requirements of their common prey species.

Integrated species distribution models reveal spatiotemporal patterns of human-wildlife conflict.

To mitigate human-wildlife conflict it is imperative to know where and when conflict occurs. However, standard methods used to predict the occurrence of human-wildlife conflict often fail to recognize how a species distribution likely limits where and when conflict may happen. As such, methods that predict human-wildlife conflict could be improved if they could identify where conflict will occur relative to species' underlying distribution. To this end, we used an integrated species distribution model that combined presence-only wildlife complaints with data from a systematic camera trapping survey throughout Chicago, Illinois. This model draws upon both data sources to estimate a latent distribution of species; in addition, the model can estimate where conflict is most likely to occur within that distribution. We modeled the occupancy and conflict potential of coyote (Canis latrans), Virginia opossum (Didelphis virginiana), and raccoon (Procyon lotor) as a function of urban intensity, per capita income, and home vacancy rates throughout Chicago. Overall, the distribution of each species constrained the spatiotemporal patterns of conflict throughout the city of Chicago. Within each species distribution, we found that human-wildlife conflict was most likely to occur where humans and wildlife habitat overlap (e.g., featuring higher-than-average canopy cover and housing density). Furthermore, human-wildlife conflict was most likely to occur in high-income neighborhoods for Virginia opossum and raccoon, despite the fact that those two species have higher occupancy in low-income neighborhoods. As such, knowing where species are distributed can inform guidelines on where wildlife management should be focused, especially if it overlaps with human habitats. Finally, because this integrated model can incorporate data that have already been collected by wildlife managers or city officials, this approach could be used to develop stronger collaborations with wildlife management agencies and conduct applied research that will inform landscape-scale wildlife management.

Humans Are More Influential Than Coyotes on Mammalian Mesopredator Spatiotemporal Activity Across an Urban Gradient

For mammalian mesopredators, human-dominated landscapes offer a mosaic of risk and reward. While the reward of anthropogenic food resources may attract mesopredators to human-dominated areas, increased mesopredator activity and abundance in these areas may cause interspecific conflict. For smaller-bodied mesopredators, the perceived risk of intraguild predation by larger mesopredators may be enough to drive spatial and temporal avoidance strategies to reduce risk while still benefiting from anthropogenic resources. We evaluated how the spatiotemporal activity of four non-canid mammalian mesopredators – raccoon (Procyon lotor), striped skunk (Mephitis mephitis), opossum (Didelphis virginiana), and domestic cat (Felis catus) – might change in the presence of an intraguild predator, the coyote (Canis latrans), and a “super predator,” humans. We quantified mesopredator activity by deploying camera traps at 110 sites across an urban gradient in the Sacramento Metropolitan Area in central California, USA. We hypothesized that mesopredators would likely change their spatiotemporal activity in response to urban intensity (H1), coyotes (H2), human presence (H3), and if urban intensity might mediate the response to humans and coyotes (H4). We used single-species occupancy models to test how mesopredators responded to different spatial scales of urbanization, as well as the temporal presence of coyotes and humans. Top single-species models then informed two-species conditional occupancy models to evaluate how mesopredators responded to “dominant” coyotes. Finally, we used temporal overlap analyzes to evaluate whether activity patterns of mesopredators changed in response to humans and coyotes across three levels of urban intensity. Mesopredators did not change their spatial or temporal activity across the urban gradient when coyotes were present. Additionally, coyotes did not influence mesopredator temporal activity at 1-3-day scales; however, raccoons and cats may avoid coyotes at finer scales. Humans influenced mesopredator detectability, as cats and coyotes avoided humans after 1 and 2 days respectively, and opossums avoided urban areas when humans were present within 3 days. Coyotes may play a limited role in altering smaller-bodied mesopredator activity, especially when humans are present. While the impacts of human presence and urban features are often linked, mesopredators may perceive the risk each poses differently, and adjust their activity accordingly.

Influence of landscape attributes on Virginia opossum density

AbstractThe Virginia opossum (Didelphis virginiana), North America's only marsupial, has a range extending from southern Ontario, Canada, to the Yucatan Peninsula, Mexico, and from the Atlantic seaboard to the Pacific. Despite the Virginia opossum's taxonomic uniqueness in relation to other mammals in North America and rapidly expanding distribution, its ecology remains relatively understudied. Our poor understanding of the ecology of this important mesopredator is especially pronounced in the rural southeastern United States. Our goal was to estimate effects of habitat on opossum density within an extensive multi‐year spatial capture‐recapture study. Additionally, we compared the results of this spatial capture‐recapture analysis with a simple relative abundance index. Opossum densities in the relatively underdeveloped regions of the southeastern United States were lower compared to the more human‐dominated landscapes of the Northeast and Midwest. In the southeastern United States, Virginia opossums occurred at a higher density in bottomland swamp and riparian hardwood forest compared to upland pine (Pinus spp.) plantations and isolated wetlands. These results reinforce the notion that the Virginia opossum is commonly associated with land cover types adjacent to permanent water (bottomland swamps, riparian hardwood). The relatively low density of opossums at isolated wetland sites suggests that the large spatial scale of selection demonstrated by opossums gives the species access to preferable cover types within the same landscape.