Genetic Monitoring for Managers
Types of GEM
Category 1a GeM Project
Example: Genetic variation
Candidate gene microsatellite variation is associated with parasitism
in wild bighorn sheep.
The 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.
|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
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.