USFWS
Genetic Monitoring for Managers
Alaska

 

Types of GEM

Category 1a GeM Project Example: Genetic variation

Candidate gene microsatellite variation is associated with parasitism in wild bighorn sheep.

Luikart et al. 2008

types variation fig 1The loss of genetic variation in populations is thought to increase susceptibility to parasites. Bighorn sheep (Ovis canadensis) populations occasionally suffer dramatic, disease-induced population declines. This study predicted that individuals with lower genetic variation would suffer greater parasitism.

Luikart et al. (2008) used non-invasive fecal sampling to measure lungworm abundance and heterozygosity in bighorn sheep at eight putatively 'neutral' microsatellite loci and at seven microsatellites located in genes of known function. Four of the seven markers were in genes related to parasite susceptibility or lung disease and thus were strong candidate genes for parasite resistance.


From 30 June - 15 August 2006, they collected sheep feces from the Mummy Range bighorn herd in Rocky Mountain National Park near Estes Park, CO. The Park's entire bighorn population had gone through several declines. Most recently, a pneumonia outbreak occurred in the mid-1990s, which reduced the population size and lamb recruitment for several years.

types variation fig 2
Regression analysis between individual heterozygosity and natural log (ln) of lungworm abundance for (a) all fifteen microsatellite loci, (b) the seven loci in genes and (c) the eight loci not in genes. [from Luikart et al. 2008]

A mark-resight study in 2003-2004 estimated that there were only approximately 300 sheep in the park, with approximately 60 of these occurring in the Mummy Range (McClintock & White 2007). Standard DNA extraction methods and microsatellite typing procedures. Protostrongylid lungworms were isolated from fecal samples by the Baermann funnel technique (Foreyt 2001). Lungworm abundance (i.e., number) was estimated as the number of larvae per gram of feces.

Luikart et al. (2008) found that lungworm (Protostrongylus spp.) abundance was higher in bighorn sheep with lower genetic variation (heterozygosity). Heterozygotes at three of four microsatellites located within disease-related genes had lower lungworm burdens. This study corroborates theoretical findings that increased parasitism and disease may be a consequence of reduced heterozygosity in wild populations, and that certain individual loci influence parasite resistance.

Their results illustrate the usefulness of using genomic information, strong candidate genes, and non-invasive sampling for monitoring both genetic variation and fitness-related traits, such as parasite resistance, in natural populations. Potentially, managers may consider augmenting small, recently bottle-necked populations to increase disease resistance by increasing genetic diversity.