Grooming in desert bighorn sheep (Ovis canadensis mexicana) and the ghost of parasites past

Ectoparasites such as ticks have a negative effect on host fitness,whereas parasite-defense grooming is effective in removing ticks.The central control (programmed grooming) model proposes thatanimals engage in preventive tick-defense grooming in responseto an internal timing mechanism, even in the absence of peripheralstimulation from parasites. This model predicts that smalleranimals will groom more frequently than larger ones becauseof the higher cost of parasitism for a small animal (body sizeprinciple). The peripheral stimulation (stimulus driven) modelpredicts no size-related differences in grooming rate in theabsence of tick bite irritation. We observed grooming behaviorin a Chihuahuan desert population of bighorn sheep (Ovis canadensismexicana), where ticks have been absent for perhaps thousandsof years. Although not exposed to ticks, bighorns self groomedby means of oral and scratch grooming, albeit at very low ratescompared to size-matched ungulates in both tick-infested andtick-free environments. Logistic regression and general linearmodels revealed both the probability that grooming was performedduring a 10-min focal sample and the rate of grooming when itoccurred was greater for younger, smaller age/sex categoriesof less body mass. Oral and scratch grooming were negativelyassociated with body mass during both years, with juveniles(X = 15 kg) grooming the most frequently and the oldest males(X = 70–85 kg) grooming the least. Assuming that programmedgrooming evolved in a tick-infested environment, the currentgrooming behavior of this population is a relict of their ancestralenvironment, an adaptation to the "ghost of parasites past."     

Psoroptic scabies in Rocky Mountain bighorn sheep (Ovis canadensis canadensis) from Wyoming

Thirteen Rocky Mountain bighorn sheep (Ovis canadensis canadensis) with clinical signs of psoroptic scabies were captured in Wyoming. Signs included droopy ears, depilation on the head and neck, and exudate in the ears. Mites were identified as either Psoroptes cervinus or P. equi. Two ewes with scabies at the time of original capture had no clinical signs of mite infection 1 and 2 yr later.     

Genomic association with pathogen carriage in bighorn sheep (Ovis canadensis)

Genetic composition can influence host susceptibility to, and transmission of, pathogens, with potential population‐level consequences. In bighorn sheep (Ovis canadensis), pneumonia epidemics caused by Mycoplasma ovipneumoniae have been associated with severe population declines and limited recovery across North America. Adult survivors either clear the infection or act as carriers that continually shed M. ovipneumoniae and expose their susceptible offspring, resulting in high rates of lamb mortality for years following the outbreak event. Here, we investigated the influence of genomic composition on persistent carriage of M. ovipneumoniae in a well‐studied bighorn sheep herd in the Wallowa Mountains of Oregon, USA. Using 10,605 SNPs generated using RADseq technology for 25 female bighorn sheep, we assessed genomic diversity metrics and employed family‐based genome‐wide association methodologies to understand variant association and genetic architecture underlying chronic carriage. We observed no differences among genome‐wide diversity metrics (heterozygosity and allelic richness) between groups. However, we identified two variant loci of interest and seven associated candidate genes, which may influence carriage status. Further, we found that the SNP panel explained ~55% of the phenotypic variance (SNP‐based heritability) for M. ovipneumoniae carriage, though there was considerable uncertainty in these estimates. While small sample sizes limit conclusions drawn here, our study represents one of the first to assess the genomic factors influencing chronic carriage of a pathogen in a wild population and lays a foundation for understanding genomic influence on pathogen persistence in bighorn sheep and other wildlife populations. Future research should incorporate additional individuals as well as distinct herds to further explore the genomic basis of chronic carriage.     

Seroprevalence of Toxoplasma gondii in Rocky Mountain bighorn sheep (Ovis canadensis)

Serum samples from 697 Rocky Mountain bighorn sheep (Ovis canadensis) from North America were examined for antibodies to Toxoplasma gondii by the modified agglutination test incorporating mercaptoethanol and formalin-fixed tachyzoites. Antibodies to T. gondii were found in 25 of 697 (3.6%) sheep in titers of 1:25 (8 sheep), 1:50 (4 sheep), 1:100 (7 sheep), 1:200 (1 sheep), 1:400 (1 sheep), 1:800 (1 sheep), and 1:1,600 (3 sheep). This is the first record of T. gondii exposure in bighorn sheep.     

Squamous cell carcinoma in a free-ranging bighorn sheep (Ovis canadensis californiana)

An oral squamous cell carcinoma which invaded maxillary bones with metastasis to the right retropharyngeal lymph node was diagnosed in a free-ranging California bighorn sheep (Ovis canadensis californiana) from Washington. Much of the maxillae had been replaced with tumor and reactive tissue, and many teeth were missing or loose. The tumor was predominantly confined to the shape of the maxillary bones and was unusual because it was bilaterally symmetrical.     

Comparison of pulmonary defense mechanisms in Rocky Mountain bighorn (Ovis canadensis canadensis) and domestic sheep

Alveolar macrophages were obtained from Rocky Mountain bighorn sheep (Ovis canadensis canadensis) and domestic sheep for the purpose of comparing pulmonary host defense mechanisms in the two species. Specific variables studied included (1) characterization of the cell types present in the lung, (2) alveolar macrophage phagocytic and bactericidal functions, (3) measurement of protein levels in lavage fluid, and (4) measurement of cortisol levels in lavage fluid. While phagocytic cell populations were similar between bighorn and domestic sheep, a significantly higher percentage of lymphocytes were present in bighorns than domestics (20% in bighorn versus 6% in domestic sheep). Significant differences were not observed in the phagocytic or bactericidal functions of macrophages between the two species. Significant differences were not observed in either lavage fluid protein levels or in cortisol levels.     

Survival of bighorn sheep (Ovis canadensis) commingled with domestic sheep (Ovis aries) in the absence of Mycoplasma ovipneumoniae

To test the hypothesis that Mycoplasma ovipneumoniae is an important agent of the bighorn sheep (Ovis canadensis) pneumonia that has previously inevitably followed experimental commingling with domestic sheep (Ovis aries), we commingled M. ovipneumoniae-free domestic and bighorn sheep (n=4 each). One bighorn sheep died with acute pneumonia 90 days after commingling, but the other three remained healthy for >100 days. This unprecedented survival rate is significantly different (P=0.002) from that of previous bighorn-domestic sheep contact studies but similar to (P>0.05) bighorn sheep survival following commingling with other ungulates. The absence of epizootic respiratory disease in this experiment supports the hypothesized role of M. ovipneumoniae as a key pathogen of epizootic pneumonia in bighorn sheep commingled with domestic sheep.     

Birthdate and survival in bighorn lambs (Ovis canadensis)

The relationship between parturition date and lamb survival was investigated among individually marked bighorn ewes in south-western Alberta, Canada. Lambs were born from 17 May to 21 July. Most births occurred in the first two weeks of the lambing period. Lambs born in May enjoyed greater survival than lambs born in June and July. The viability of lambs born after 10 June was extremely low. Inadequate nutrition is suggested as the cause of greater mortality of lateborn lambs. Ewes that give birth late are at an earlier stage of lactation when forage quality declines and may not produce sufficient milk to ensure lamb survival. Their lambs have access to high-quality forage for a shortened period. The proportion of late lambs appeared to be correlated with ewe density in the winter range.     

Response of vaccinated and unvaccinated bighorn sheep (Ovis canadensis canadensis) to experimental respiratory syncytial virus challenge

Five Rocky Mountain bighorn sheep (Ovis canadensis canadensis), approximately 5 mo old and without detectable antibody titers to respiratory syncytial virus (RSV), were assigned to two groups to study the effects of RSV challenge inoculation in vaccinated (n = 3) and unvaccinated (n = 2) bighorns. The three lambs vaccinated with a modified live bovine RSV vaccine developed a detectable antibody response to the vaccine. Vaccinated and unvaccinated lambs challenged with an ovine isolate of RSV developed increased levels of neutralizing antibody, but clinical signs of disease were not observed. Neutralizing antibody titers to RSV remained higher (2-4-fold) in vaccinated lambs over time when compared to unvaccinated lambs.     

Transplacental transmission of Protostrongylus sp. in California bighorn sheep (Ovis canadensis californiana) in Oregon

Transplacental transmission of Protostrongylus sp. was documented for the first time in California bighorn sheep (Ovis canadensis californiana) by recovery of third stage larvae from two fetuses.     

Characterizing population and individual migration patterns among native and restored bighorn sheep (Ovis canadensis)

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Genomic consequences of genetic rescue in an insular population of bighorn sheep (Ovis canadensis)

Genetic rescue is a management intervention whereby a small population is supplemented with individuals from other populations in an attempt to reverse the effects of inbreeding and increased genetic load. One such rescue was recently documented in the population of bighorn sheep (Ovis canadensis) within the National Bison Range wildlife refuge (Montana, USA). Here, we examine the locus-specific effects of rescue in this population using a newly developed genome-wide set of 195 microsatellite loci and first-generation linkage map. We found that the rate of introgression varied among loci and that 111 loci, 57% of those examined, deviated from patterns of neutral inheritance. The most common deviation was an excess of homozygous genotypes relative to neutral expectations, indicative of directional selection. As in previous study of this rescue, individuals with more introduced alleles had higher reproductive success and longevity. In addition, we found 30 loci, distributed throughout the genome, which seem to have individual effects on these life history traits. Although the potential for outbreeding depression is a major concern when translocating individuals between populations, we found no evidence of such effects in this population.     

Freemartinism in a captive herd of Rocky Mountain bighorn sheep (Ovis canadensis).

Freemartinism in two animals from a captive herd of Rocky Mountain bighorn sheep (Ovis canadensis) at the Denver Zoological Gardens (Denver, Colorado, USA) is described. A young ewe had female external genitalia, a masculine appearance, and demonstrated male behavior as she matured. Another ewe with female external genitalia died as a yearling. Necropsy revealed a non-patent vagina and internal male genitalia. Both females were chimeric with karyotypes containing XX and XY sex chromosomes.