Dissertation
Research: Functional genetic diversity and pathogen
resistance in black-tailed prairie dogs
Field Site:
Short Grass Steppe Long Term Ecological Research site; Pawnee National
Grassland Keywords: conservation genetics; disease ecology; immunogenetics
Wildlife face ever-increasing threats from emerging pathogens, many
that also cause disease in humans.Genetic
diversity may play an important role in buffering populations against
disease.The genes encoding
the major histocompatibility complex (MHC) of the vertebrate immune
system have been widely used to discern relationships between genetic
diversity and disease.However,
the relationship between disease and MHC diversity remains unclear,
likely because other immune system genes are also important in responses
to pathogens and parasites.
Prairie dogs (Cynomys
spp.) are social rodents that live in distinct colonies made up of
territorial family groups with limited interactions.Prairie dogs are an important component of North American
grasslands, but have declined throughout their range, in part because of
the introduced pathogen Yersinia pestis, the causative agent of plague.I performed a literature search for parasites of black-tailed
prairie dogs, and found records for 37 pathogen and parasite species.Given the potential parasite diversity in black-tailed prairie
dogs, evidence of disease-induced decline, their taxonomic relationship
to several species of conservation concern, and our previous studies of
populations in northern Colorado, prairie dogs are an excellent model
for associations between pathogen resistance and functional genetic
diversity in mammals.
The vast majority of association studies in wild
vertebrates focus on the relationship between a single pathogen and one
or a few MHC genes.I am
going beyond the single-pathogen single-gene approach by investigating
the relationship between allelic diversity (heterozygosity) in four
functionally different immune system genes and the entire parasite
community of black-tailed prairie dogs.
I hypothesize that individuals with greater immunogenetic diversity will
have reduced parasite diversity because particular alleles provide
pathogen resistance.Since
prairie dog colonies experience periodic plague-induced extinction
followed by recolonization, I also expect parasite community diversity
will increase through time up to an amount determined by colony size and
distance to nearest neighboring colony.
I am live-trapping prairie dogs on several colonies on
the Short Grass Steppe Long Term Ecological Research Site, controlling
for size, location, and time since the last extinction event.For each captured animal I am quantifying parasite abundance and
diversity, recording standard measures of body condition and relevant
immune responses (cell-mediated and humoral), and resolving
immunogenetic diversity, compared to neutral markers (microsatellites),
using SSCP analysis and sequence data. All animals are returned to
the point of capture.
Conservation genetic studies typically use
neutral genetic markers (e.g., microsatellites) to investigate
relationships between genetic diversity and fitness.While neutral markers are valuable in discerning population
structure and gene flow, their relationship to fitness has been
questioned.Measuring
functional genetic variation related to specific ecological/
evolutionary processes (parasitism) is more relevant in determining a
species' ability to adapt to a changing environment. I hope that
results from this research will be useful in developing conservation
plans for all five species of prairie dogs. Marker development for
functional genes should also be useful in developing functional genetic
markers in other wildlife species.
I
am also using existing literature to assemble a database of
host-parasite relationships of vertebrate species found on the
Shortgrass Steppe Long Term Ecological Research Site in eastern Colorado,
in order to explore the relationships between host species interactions,
host traits, and the diversity and characteristics of their parasites.
