FLAVOR PREFERENCE AND EFFICACY OF VARIABLE DOSE ONTARIO RABIES VACCINE BAIT (ONRAB) DELIVERY IN STRIPED SKUNKS ( MEPHITIS MEPHITIS).

In North America, terrestrial wildlife rabies control is achieved by oral rabies vaccination programs that principally target mesocarnivores. Success at rabies control in striped skunks ( Mephitis mephitis) has been more limited and may require additional enhancements to existing bait products or novel bait designs and attractants. We evaluated preference among captive striped skunks for six different flavors of placebo Ontario Rabies Vaccine Bait (ONRAB®) "Ultralite" Baits (Artemis Technologies, Guelph, Ontario, Canada). Different doses and delivery methods of ONRAB vaccine were tested for efficacy in a subsequent experiment with the same skunks. Cheese-, egg-, and chicken-flavored baits were preferred over plain-flavored baits, but a strong preference for a singular flavor was not observed. Vaccine efficacy of 80-100% was observed among skunks challenged at 335 d postvaccination across a log range of doses tested by a direct instillation into the oral cavity route, respectively (109.3-1010.2 median tissue culture infective doses), in contrast to more-limited efficacy by bait delivery. Our results extended the duration of ONRAB vaccine efficacy in skunks and suggested that there may be limited flexibility to alter vaccine titer and volume in novel bait designs for skunks.

Visual acuity in the striped skunk (Mephitis mephitis).

The visual acuity of striped skunks (Mephitis mephitis) was tested using a 2 alternative forced-choice task with square wave gratings. Skunks were reinforced with food items for touching a ball in front of a striped stimulus when paired with a ball in front of a solid gray stimulus. Skunks demonstrated a maximum visual acuity of 0.42 cycles per degree when tested with bright outdoor illumination. This poor visual acuity may be due to their nocturnal lifestyle, lack of predation, and is consistent with their preferential use of smell and sound during foraging. (PsycINFO Database Record

Resampling method for applying density-dependent habitat selection theory to wildlife surveys.

Isodar theory can be used to evaluate fitness consequences of density-dependent habitat selection by animals. A typical habitat isodar is a regression curve plotting competitor densities in two adjacent habitats when individual fitness is equal. Despite the increasing use of habitat isodars, their application remains largely limited to areas composed of pairs of adjacent habitats that are defined a priori. We developed a resampling method that uses data from wildlife surveys to build isodars in heterogeneous landscapes without having to predefine habitat types. The method consists in randomly placing blocks over the survey area and dividing those blocks in two adjacent sub-blocks of the same size. Animal abundance is then estimated within the two sub-blocks. This process is done 100 times. Different functional forms of isodars can be investigated by relating animal abundance and differences in habitat features between sub-blocks. We applied this method to abundance data of raccoons and striped skunks, two of the main hosts of rabies virus in North America. Habitat selection by raccoons and striped skunks depended on both conspecific abundance and the difference in landscape composition and structure between sub-blocks. When conspecific abundance was low, raccoons and striped skunks favored areas with relatively high proportions of forests and anthropogenic features, respectively. Under high conspecific abundance, however, both species preferred areas with rather large corn-forest edge densities and corn field proportions. Based on random sampling techniques, we provide a robust method that is applicable to a broad range of species, including medium- to large-sized mammals with high mobility. The method is sufficiently flexible to incorporate multiple environmental covariates that can reflect key requirements of the focal species. We thus illustrate how isodar theory can be used with wildlife surveys to assess density-dependent habitat selection over large geographic extents.

Effect of age and ration on diet-tissue isotopic (Δ13C, Δ15N) discrimination in striped skunks (Mephitis mephitis).

An important prerequisite for the effective use of stable isotopes in animal ecology is the accurate assessment of isotopic discrimination factors linking animals to their diets for a multitude of tissue types. Surprisingly, these values are poorly known in general and especially for mammalian carnivores and omnivores in particular. Also largely unknown are the factors that influence diet-tissue isotopic discrimination such as nutritional quality and age. We raised adult and juvenile striped skunks (Mephitis mephitis) in captivity on a constant omnivore diet (Mazuri Omnivore A 5635). Adults (n=6) and juveniles (n=3) were kept for 7 months and young (n=7) to the age of 50 days. We then examined individuals for stable carbon (δ(13)C) and nitrogen (δ(15)N) isotope values of hair, nails, lipid, liver, muscle, bone collagen and the plasma, and cellular fractions of blood. Discrimination values differed among age groups and were significantly higher for young compared with their mothers, likely due to the effects of weaning. Δ(15)N isotopic discrimination factors ranged from 3.14 (nails) to 5.6‰ (plasma) in adults and 4.3 (nails) to 5.8‰ (liver) for young. For Δ(13)C, values ranged from-3.3 (fat) to 3.0‰ (collagen) in adults and from-3.3 (fat) to 2.0‰ (collagen) in young. Our data provide an important tool for predicting diets and source of feeding for medium-sized mammalian omnivorous adults integrated over short (e.g. liver, plasma) through long (e.g. collagen) periods and underline the potential effects of age on isotopic values in omnivore diets.

Physiological adaptations to prolonged fasting in the overwintering striped skunk (Mephitis mephitis).

Wintertime physiology of captive striped skunks (Mephitis mephitis) in response to cold ambient temperature (Ta) and fasting was investigated with body temperature (Tb) and activity recordings and analyses of hematology, plasma biochemistry and tissue fatty acids (FA). After 105 days of food deprivation, the skunks were in phase II of fasting indicated by the elevated plasma nonesterified FA and glycerol but no accumulation of nitrogen end products. Shorter-chain saturated and monounsaturated FA together with C18-20 n-3 polyunsaturated FA were preferentially mobilized. Individual amino acids responded to fasting in a complex manner, while essential and nonessential amino acid sums remained stable. Increases in hemoglobin and hematocrit suggested dehydration. The activity levels were lower in mid-January-early March, and the activity bouts were mostly displayed between 17:00-23:00 h. Daily torpor was observed in two females with 29 and 46 bouts. The deepest torpor (Tb<31 °C) occurred between dawn and early afternoon and lasted for 3.3 ± 0.18 h. The average minimum Tb was 29.2 ± 0.15 °C and the lowest recorded Tb was 25.8 °C. There was significant relation between the average 24-h Tb and Ta. Increases in wintertime Ta, as predicted by climate change scenarios, could influence torpor patterns in the species.

Field immobilization of Molina's hog-nosed skunk (Conepatus chinga) using ketamine and xylazine.

We injected 27 adult Molina's hog-nosed skunks (Conepatus chinga) intramuscularly by hand with ketamine hydrochloride (KH) and xylazine hydrochloride (XH) in the Pampas grassland of Argentina. Skunks were immobilized with a mean (±SD) dosage of 24.9±6.5 mg/kg KH and 1.9±0.6 mg/kg XH. The mean effective dosages of KH (27.6 mg/kg) and XH (1.7 mg/kg) were higher and lower, respectively, than those reported in skunks previously. Mean induction and recovery time were 5.3±1.9 min and 47.7±18.5 min, respectively. Hypothermia was the only problem detected in field immobilization and occurred in winter but did not appear to be associated with to drug doses. We conclude that KH/XH is a safe immobilizing drug combination for Molina's hog-nosed skunk.

Measuring and selecting scales of effect for landscape predictors in species-habitat models.

Wildlife managers often use habitat models to determine species habitat requirements and to identify locations for conservation efforts, uses which depend on accurate specification of species-habitat relationships. Prior study suggests that model performance may be influenced by the way we measure environmental predictors. We hypothesized that species responses to landscape predictors are best represented by landscape composition-based measurements, rather than distance-based measurements. We also hypothesized that models using empirical data to select an appropriate scale of effect for each habitat predictor (multi-scale models) should perform better than models that assume a common scale of effect for all predictors (single-scale models). To test these hypotheses we constructed habitat models for three mammal species, Mephitis mephitis, Mustela erminea, and Procyon lotor, based on surveys conducted in 80 landscapes in southeastern Ontario, Canada. For each species we compared the performance of distance- and composition-based measurements, and we compared the performance of single- and multi-scale models. The composition-based measurement, measured at its empirically determined scale of effect, had greater explanatory power than the distance-based measurement of a given predictor more often than expected by chance, supporting our first hypothesis. Contrary to expectation, multi-scale models did not have better explanatory power or predictive performance relative to single-scale models. We identified and evaluated four potential mechanisms to explain this, and, depending on the species, we found that the best explanation was either that predictors have significant effects at a common scale or that, although the modeled effects were at multiple scales, they were of similar magnitude and direction at the scales modeled in single- and multi-scale models. Our results suggest that habitat modeling based on distance-based measurements could be improved by including composition-based measurements of landscape predictor variables, but that inclusion of predictor-specific scales of effect for composition-based measurements does not necessarily improve performance over models including composition-based measurements at a single scale. Conservation and wildlife management may be simplified when single-scale models perform as well as multi-scale models, as this suggests actions conducted at a single scale may address management objectives as well as actions taken at different scales for different landscape features.

Density-dependent nest predation in waterfowl: the relative importance of nest density versus nest dispersion.

When nest predation levels are very high or very low, the absolute range of observable nest success is constrained (a floor/ceiling effect), and it may be more difficult to detect density-dependent nest predation. Density-dependent nest predation may be more detectable in years with moderate predation rates, simply because there can be a greater absolute difference in nest success between sites. To test this, we replicated a predation experiment 10 years after the original study, using both natural and artificial nests, comparing a year when overall rates of nest predation were high (2000) to a year with moderate nest predation (2010). We found no evidence for density-dependent predation on artificial nests in either year, indicating that nest predation is not density-dependent at the spatial scale of our experimental replicates (1-ha patches). Using nearest-neighbor distances as a measure of nest dispersion, we also found little evidence for "dispersion-dependent" predation on artificial nests. However, when we tested for dispersion-dependent predation using natural nests, we found that nest survival increased with shorter nearest-neighbor distances, and that neighboring nests were more likely to share the same nest fate than non-adjacent nests. Thus, at small spatial scales, density-dependence appears to operate in the opposite direction as predicted: closer nearest neighbors are more likely to be successful. We suggest that local nest dispersion, rather than larger-scale measures of nest density per se, may play a more important role in density-dependent nest predation.

Does encephalization correlate with life history or metabolic rate in Carnivora?

A recent analysis of brain size evolution reconstructed the plesiomorphic brain-body size allometry for the mammalian order Carnivora, providing an important reference frame for comparative analyses of encephalization (brain volume scaled to body mass). I performed phylogenetically corrected regressions to remove the effects of body mass, calculating correlations between residual values of encephalization with basal metabolic rate (BMR) and six life-history variables (gestation time, neonatal mass, weaning time, weaning mass, litter size, litters per year). No significant correlations were recovered between encephalization and any life-history variable or BMR, arguing against hypotheses relating encephalization to maternal energetic investment. However, after correcting for clade-specific adaptations, I recovered significant correlations for several variables, and further analysis revealed a conserved carnivoran reproductive strategy, linking degree of encephalization to the well-documented mammalian life-history trade-off between neonatal mass and litter size. This strategy of fewer, larger offspring correlating with increased encephalization remains intact even after independent changes in encephalization allometries in the evolutionary history of this clade.

Nutrition and behavior of striped skunks.

Skunks are an integral part of the environment and a fascinating component of the earth's biodiversity. Their behavioral idiosyncrasies, made possible by their unique method of defense, make them entertaining to watch in the wild, and their beneficial habits far outweigh any potential negative attributes. Striped skunks can be a benefit in urban and agricultural areas because they prey on harmful and damaging insects and rodents that plague gardens and crops. The general public should be encouraged to live in harmony with skunks, as opposed to viewing them as nuisances. Keeping captive or pet skunks should be considered only after feeding, care, disease, and legal information has been investigated.

Energetic consequences and ecological significance of heterothermy and social thermoregulation in striped skunks (Mephitis mephitis).

We assessed patterns and energetic consequences of different overwintering strategies, torpor, and social thermoregulation in the striped skunk (Mephitis mephitis) under natural ambient temperature and photoperiod. Striped skunks entered spontaneous daily torpor, with the lowest torpid body temperature (T(b)) reaching 26.0 degrees C, the lowest recorded T(b) for a carnivore. Patterns of daily torpor differed between solitary and grouped skunks: all solitary skunks regularly entered daily torpor, but only some individuals in communal dens employed torpor. When they did, it was shallow and infrequent. Solitary skunks entered torpor on average 50 times (in 120 d) compared with 6 times for grouped skunks. During torpor, solitary skunks had average minimum T(b) of 26.8 degrees C and bout duration of 7.8 h, whereas grouped skunks had average minimum T(b) of 30.9 degrees C and bout duration of 5.4 h. Torpor by solitary skunks occurred during their activity phase, but grouped skunks' shallow torpor bouts were restricted to their diurnal resting phase. On average, grouped skunks experienced lower percent daily fat loss, and they emerged in spring with higher percent body fat of 25.5%. In contrast, solitary skunks emerged in spring with only 9.3% body fat. In conclusion, the use of daily torpor and social thermoregulation in northern populations of striped skunks represent two strikingly different mechanisms to minimize energetic costs and increase individual fitness in response to unfavorable environmental conditions.

Coupling stable isotopes with bioenergetics to estimate interspecific interactions.

Interspecific interactions are often difficult to elucidate, particularly with large vertebrates at large spatial scales. Here, we describe a methodology for estimating interspecific interactions by combining stable isotopes with bioenergetics. We illustrate this approach by modeling the population dynamics and species interactions of a suite of vertebrates on Santa Cruz Island, California, USA: two endemic carnivores (the island fox and island spotted skunk), an exotic herbivore (the feral pig), and their shared predator, the Golden Eagle. Sensitivity analyses suggest that our parameter estimates are robust, and natural history observations suggest that our overall approach captures the species interactions in this vertebrate community. Nonetheless, several factors provide challenges to using isotopes to infer species interactions. Knowledge regarding species-specific isotopic fractionation and diet breadth is often lacking, necessitating detailed laboratory studies and natural history information. However, when coupled with other approaches, including bioenergetics, mechanistic models, and natural history, stable isotopes can be powerful tools in illuminating interspecific interactions and community dynamics.

Effects of surgical implantation of temperature dataloggers on reproduction of captive striped skunks (Mephitis mephitis).

A total of 20 (14 females, six males) captive striped skunks (Mephitis mephitis) with miniature temperature dataloggers implanted free in the abdominal cavity were examined for reproductive performance and pathology because of implants. Eleven of 12 female skunks reproduced successfully 45.9+/-3.7 days after surgery to remove implanted dataloggers. The pregnancy rate of 91.7% (11/12) was much higher than other captive studies and was comparable with that of wild skunks. Eight striped skunks (six males, two females) that were euthanatized and necropsied after having implants in the abdominal cavity for 5 mo showed no apparent pathology associated with the implant. Implantation of the intraperitoneal devices did not lead to complications in abdominal tissues. Neither implant nor surgery affected reproduction. We conclude that implanted dataloggers can safely be used in physiologic studies of striped skunks or possibly other small carnivores in captive or field studies.

Changes in uterine expression of leukemia inhibitory factor receptor gene during pregnancy and its up-regulation by prolactin in the western spotted skunk.

The multifunctional cytokine leukemia inhibitory factor (LIF) is presumed to participate in preparing the uterus for blastocyst implantation. Increased production of LIF is positively correlated with termination of embryonic diapause and preparation for implantation in the spotted skunk. This study examined changes in the expression, localization, and hormonal regulation of LIF receptor (LIFRbeta) gene expression in the uterus of the skunk. Changes in the uterine concentration of LIFRbeta mRNA during pregnancy or in response to hormones after ovariectomy were determined by Northern hybridization analysis and reverse-transcriptase polymerase chain reaction. The skunk uterus produces two LIFRbeta transcripts, the levels of which increase in concentration when the blastocysts resume their development but then decline somewhat during the latter stage of blastocyst activation. Ovariectomy significantly reduced uterine LIFRbeta expression. Estradiol and/or progesterone failed to significantly elevate LIFRbeta mRNA levels in ovariectomized animals. Prolactin significantly increased uterine concentrations of LIFRbeta mRNA to greater than those of ovariectomized controls, but these levels were not comparable to those observed during preimplantation. The LIFRbeta mRNA was predominately localized to stromal cells surrounding the uterine glands and in yolk sac endoderm, syncytiotrophoblast, and cytotrophoblast of postimplantation embryos.

Spatiotemporal expression of cyclooxygenase 1 and cyclooxygenase 2 during delayed implantation and the periimplantation period in the Western spotted skunk.

Embryonic development in the western spotted skunk is arrested after blastocyst formation for about 200 days. This developmental arrest is believed to be due to insufficiency of uterine conditions to support continuous development. Implantation and decidualization are defective in cyclooxygenase 2 (Cox2)-, but not Cox1-, deficient mice. We therefore used Northern and in situ hybridization to investigate changes in uterine expression of Cox1 and Cox2 genes during various stages of pregnancy in the spotted skunk. Cox1 was constitutively expressed at all stages of pregnancy examined, but it did exhibit localized up-regulation in the trophoblast and necks of uterine glands at early implantation sites. Cox2 expression was highly regulated with little or no expression during delayed implantation. Cox2 expression was first detected in the uterus and trophoblast prior to blastocyst attachment and remained detectable for 5-6 days after blastocyst attachment. Cox2 expression was also localized in the luminal and glandular epithelia of uterine segments located between implantation chambers. Changes in Cox expression were not correlated with the abrupt increase in uterine weight that occurs simultaneously with renewed embryonic development but was correlated with an influx of serum proteins into the uterus observed in a previous study.

Field immobilization of pygmy spotted skunks from Mexico.

We immobilized 21 pygmy spotted skunks (Spilogale pygmaea), in the tropical deciduous forest at the Chamela Biological Station (Mexico) from October 1994 to May 1997, with a mixture of ketamine (KH) and xylazine (XH). Skunks were immobilized with a mean (+/- SD) dosage of 15.7 +/- 8.3 mg/kg KH and 8.1 +/- 4.3 mg/kg XH. Mean induction and recovery time (n = 21) were 1.7 +/- 1.6 and 34.2 +/- 12.2 min, respectively. One individual was immobilized with XH, induction time was 1 min, and recovery time was 45 min. Foaming salivation was observed in this animal. No other adverse effects were observed for the other animals in this sample.

Population and movement characteristics of radio-collared striped skunks in North Dakota during an epizootic of rabies.

We observed a total of 102 striped skunks (Mephitis mephitis) from March to July of both 1991 and 1992 in Stutsman County, North Dakota (USA) during an experiment with food supplementation. Twenty-three apparently healthy skunks in 1991 and 56 in 1992 were equipped with radio-collars. In 1991, one of the 23 was tested and found to be rabid. In 1992, 50 of 56 were tested; 35 (70%) were rabid. Of skunks with ages estimated, 19 (66%) of 29 were first year animals in 1991 compared with nine (22%) of 41 first year animals in 1992. All 18 females captured in 1991 were pregnant or parous compared with 21 (60%) of 35 in 1992. The estimated survival rate of skunks was 0.85 during April to June 1991, but only 0.17 during April to July 1992. In 1992, the survival rate of first year skunks was 0.08, compared with 0.35 for older animals. Eleven (31%) of 36 skunks found dead of rabies or in late clinical stage were located below ground. We detected no differences in 1992 between healthy and rabid skunks in estimated mean (+/- SE) rate of travel (232 +/- 14 m/hr), distance traveled (2,047 +/- 141 m/night), or home range size (1.6 +/- 0.4 km2) during half-month periods from April through June. Among rabid skunks, mean rate of travel tended to decrease from 298 +/- 48 m/hr during the 14 days preceding the clinical period of rabies (pre-clinical) to 174 +/- 48 m/hr during the clinical period of rabies (14 days immediately before death). Similar decrease occurred in distance traveled in a night (2,318 +/- 281 m, pre-clinical; 1,497 +/- 281 m, clinical). Mean home range size of males (2.8 +/- 0.4) was greater than of females (1.2 +/- 0.4) during the pre-clinical period, but during the clinical period home range sizes of males (1.8 +/- 0.4) and females (1.8 +/- 0.4) were similar. Mean home range size of females did not differ between pre-clinical (1.2 +/- 0.4) and clinical (1.8 +/- 0.4) periods (P = 0.22). Deaths of skunks from rabies in 1992 tended to be more spatially clumped than expected had they been random, mostly due to deaths detected before 8 May. We detected no correlation between locations of animals found dead of rabies and dates of death.

Phylogenetic relationships within caniform carnivores based on analyses of the mitochondrial 12S rRNA gene.

The complete 12S rRNA gene of 32 carnivore species, including four feliforms and 28 caniforms, was sequenced. The sequences were aligned on the basis of their secondary structures and used in phylogenetic analyses that addressed several evolutionary relationships within the Caniformia. The analyses showed an unresolved polytomy of the basic caniform clades; pinnipeds, mustelids, procyonids, skunks, Ailurus (lesser panda), ursids, and canids. The polytomy indicates a major diversification of caniforms during a relatively short period of time. The lesser panda was distinct from other caniforms, suggesting its inclusion in a monotypic family, Ailuridae. The giant panda and the bears were joined on the same branch. The skunks are traditionally included in the family Mustelidae. The present analysis, however, showed a less close molecular relationship between the skunks and the remaining Mustelidae (sensu stricto) than between Mustelidae (sensu stricto) and Procyonidae, making Mustelidae (sensu lato) paraphyletic. The results suggest that the skunks should be included in a separate family, Mephitidae. Within the Pinnipedia, the grouping of walrus, sea lions, and fur seals was strongly supported. Analyses of a combined set of 12S rRNA and cytochrome b data were generally consistent with the findings based on each gene.

Progression of trophoblast into the endometrium during implantation in the western spotted skunk.

BACKGROUND: In mustelid carnivores, several blastocysts become implanted either approximately 12 days following fertilization or after a delay of implantation. In the western spotted skunk, implantation occurs following a long period of delayed implantation and a brief activation stage. Within each implantation chamber, a large number of trophoblastic plaques form, and the syncytial trophoblast of these plaques adheres to and penetrates into the uterine luminal epithelium. The presence of multiple attachment sites was used to analyse the way in which trophoblast adheres to, penetrates, and removes uterine epithelium and its subsequent association with the subepithelial vascular plexus. METHODS: Implantation chambers from 18 western spotted skunks were collected during the first week postimplantation and the tissue prepared for light microscopy and scanning and transmission electron microscopy. RESULTS: A series of trophoblastic plaques, which form a ring peripheral to the embryonic shield, attach to and penetrate the uterine epithelium. As new trophoblastic plaques are forming, the initial plaques enlarge and spread along the basal lamina of the luminal epithelium, and trophoblastic processes project through this basal lamina. Subsequently there is a stage of consolidation in which cytotrophoblast increases greatly in amount, attachment sites coalesce, and the luminal epithelium is eliminated. Syncytial trophoblast intrudes into endometrial gland lumina and surrounds subepithelial capillaries. CONCLUSIONS: It is suggested that the affinity of syncytial trophoblast for apical junctional complexes of uterine epithelial cells facilitates intrusion of syncytial trophoblast between cells, possibly guided by the marginal ridges of the uterine cells. The trophoblast shows no tendency to adhere to or invade maternal capillaries. This lack of adhesion to endothelial cells suggests either a change in adhesive properties of trophoblast following epithelial penetration or differences in adhesive properties between surface epithelial cells and endothelial cells. Although trophoblast differentiation appears to be chronologically regulated, it could be responding to maternally derived factors.

Changes in uterine estrogen and progesterone receptors during delayed implantation and early implantation in the spotted skunk.

Although the exact cause(s) of embryonic diapause in the western spotted skunk and other carnivores remains unknown, it has been hypothesized that it may be due to levels of ovarian hormone secretion that are insufficient to promote a uterine environment conducive to continuous embryonic development and implantation. Immunocytochemistry was used to determine whether changes in abundance or distribution of estrogen receptors (ER) and progesterone receptors (PR) may be associated with the cessation or renewal of embryonic development. Thirty pregnant skunks were killed during delayed implantation and periimplantation periods. ER and PR were detected in luminal and glandular epithelium, endometrial stroma, vasculature, and myometrium of the uterus during the period of delayed implantation. There was a significant reduction of both ER and PR receptors during the periimplantation period. The most pronounced change was the complete loss or reduction in staining intensity for PR and ER in the luminal epithelium during the first 2-3 days after implantation. These findings suggest that the failure of skunk blastocysts to undergo continuous development and implant without a prolonged period of diapause is not the result of an insufficient number of ER or PR in the uterus. The data also indicate that renewed embryonic development and implantation is not associated with an increase in these uterine steroid receptors.