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Populations: a supplement to your Text
Objective: Be able to read a research paper in
Molecular Ecology and derive conservation
recommendations from the data
What is Genetic Variation?
1) Heterozygosity of population: Percentage of genes in a population that
are polymorphic.
2) Number of alleles and frequencies for each polymorphic gene in
population.
3) Heterozygosity of each individual in population: Percentage of genes per
individual that are polymorphic, noting that in a diploid each gene can only
be heterozygous or homozygous.
Rate of loss of heterozygosity in a population per generation (Wright, 1931)
deltaF = 1/2Ne
So if population of 50 individuals, there will be a 1% decline in
heterozygosity due to loss of rare alleles.
If population of 25 individuals, decline of 2% (1/50 or 2 per 100).
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Factors that affect genetic variation:
Mutation
Mating system
Three STRONG FORCES that change allele frequencies:
1. GENE FLOW = movement of gametes, individuals or populations
2. SELECTION = a directional process that leads to an increase in frequency of
alleles or genotypes that increase individual ability to produce healthy offspring.
3. DRIFT = a process in which allele frequencies in a population change by
chance as a result of non-random carry-over (sampling error) from generation to
generation.
- leads to:
loss of alleles,
increased homozygosity,
population differentiation (if no migration/gene flow between populations).
Drift can increase in small populations due to:
fragmentation,
bottleneck = event removes all but a few individuals,
founder effect = a few individuals leave old population, start new one.
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The assumptions of the island model:
All populations are created equal, with N
individuals and equal contributions to the
migrant pool
There is NO spatial structure: in effect all
populations are equally close to all other
populations (no isolation by distance)
Everything is at equilibrium, nothing is changing.
No selection
no mutation
The fixation index is the probability of any two alleles
chosen randomly in a population having arisen from one
common ancestor. In a set of populations that exchange
NO migrants, this index increases in each subpopulation.
This means that subpopulations of a single species can
change over time (in allele frequencies and in hetero vs.
homozygosity) and become divergent from each other.
Ultimately, each subpopulation would have only certain
alleles (e.g. allele A or a) due to inbreeding.
Fst = 1/ 4Nm + 1
Fst is the equilibrium fixation index, a measure of population
divergence within a species. N is the local population size
and m is the migration rate among populations.
An Fst of 1.0 is high and indicates high divergence, little or
no migration. Zero indicates no divergence and at least
some migration.
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Grey wolves are large mammalian carnivores that can disperse over
long distances (50 - several hundred km) across major obstacles
- an individual wolf moves 50km before establishing territory.
•
Grey Wolves have social organization - packs.
•
•
Different prey for boreal forest vs. tundra/taiga wolves:
Boreal Forest wolves believed to defend permanent
territories and predate resident, nonmigrant species (deer,
elk, moose, woodland cariboo).
•
Tundra/taiga wolves believed to be territorial in summer,
but migrate with barren ground caribou in winter to
caribou breeding grounds - this is tested in our paper.
•
Tundra, taiga and boreal coniferous forest biomes are
uninterupted and intergrade, no physical barriers to
wolves or caribou.
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http://gliving.com/the-might-comeback-of-gray-wolves/
Background
information
Hypothesis/
question =
The Aim
How they did it 4 methods
Main result
Conservation
recommendation
based on result
•Sampling of wolves over a large, continuous area of forest, taiga and tundra.
•19 migrating caribou and 19 tundra wolves tracked by satellite telemetry, plus
radiocollars on 7 wolves.
•
Created 12 month data set, computed Euclidean distances.
• Blood was collected as described in caption of Fig. 1 above (26 living wolves
and tissue from pelts of 378 legally hunted wolves).
• Pelt color was classified and recorded.
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http://www.enr.gov.nt.ca/_live/pages/wpPages/caribou_in
formation.aspx
Fall/winter
Spring/summer
Results from satellite telemetry in this study prove for the first time that:
! Boreal Forest wolves do not migrate.
! Tundra/Taiga Wolves and barren ground caribou migrate north together, in spring,
over 1000 km.
! Wolves give birth in tundra summering areas (pink). Pups need to stay near the den.
! Though caribou are past calving and start moving south in summer, the simultaneous
caribou-wolf migration south is in the fall through spring of the following year.
Let’s look at one wolf and one caribou over the year…
Caribou stays in one area
in May-June
- this is the calving ground
Wolf stays in one area in
May-October,
around den and pups
Caribou and wolf are
In same location
in December
http://gliving.com/themight-comeback-of-graywolves/
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Two haploid DNA markers and one genetic trait (light coat color is
recessive): Mt DNA and coat color support hypothesis that ecology not
geography drives evolution of distinct forest vs. tundra/taiga wolf
populations.
http://gliving.com/the-mightcomeback-of-gray-wolves/
DNA markers (autosomal microsatellites, Mitochondrial DNA and Y Chromosome
haplotypes): Fst analyses show population subdivision and allele fixation based on wolf
movement, habitat and prey movement for all markers, except Y chromosome (why?)
All red highlighted and underlned results are statistically significant - see P values.
Lat not Long Association
reflects south to north migration
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The authors conclude that Tundra/Taiga
grey wolf is an Evolutionarily Significant
Unit (ESU):
What conservation recommendations do we
take away from this study?
Is the Tundra/Taiga grey wolf a new
species or is it a population? Does this
matter?
http://www.cosmosmith.com/images/tundra_wolf01a.jpg
http://gliving.com/the-might-comeback-of-gray-wolves/
Background
information
Hypothesis/
question =
The Aim
How they did it 4 methods
Main result
Conservation
recommendation
based on result
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Populations: a supplement to your Text
Objective: Be able to read a research paper in
Molecular Ecology and derive conservation
recommendations from the data
9
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Populations: a supplement to your Text
Objective: Be able to read a research paper in
Molecular Ecology and derive conservation
recommendations from the data
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