conservation genetics class 8 presentation 3. forces of evolution natural selection genetic drift ...
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Conservation Genetics
Class 8
Presentation 3
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Forces of evolution Natural selection Genetic drift Non-random mating (inbreeding) Sexual selection (differential
survival/reproduction due to mate selection) Gene flow (movement of genes from one
population to another) Mutation
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Why study genetics? One component of “biodiversity” It is the construction library of a
population or species Permits population to adapt and evolve
through natural selection Common features define a spp Variability in genes allow them to
adapt
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Genes & Environment
Genotype + Environment = Phenotype
We see the phenotype: leaf shape, colour of hair, eyes, beak size, etc.
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Value of diversity Differences in phenotype (e.g. blue
eyes vs. brown, vs.. pink) mean different capabilities under different conditions such as: night vision, tolerance to high light or UV radiation)
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Adaptive Radiation Adaptive radiation occurs when
genotypes evolve into new spp Natural selection acting on genotypes
or mutations = new species Natural selection: due to competition,
new habitat, selective predation, etc.
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Examples of adaptive radiation
Hawaiian Honey-Creepers– Finch like seed eating ancestor– Arrived about 3.5 to 8 million yrs ago– Adapted beaks to different foods
Fruit, insects, nectar (tubular with feathered tongue), seeds
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Examples of adaptive radiation
Darwin’s finches on Galapagos Islds Ancestor: ground dwelling, seed eater Today 14 spp
– Tree finches Adapted to feed on insects, sharper bill than ground
dwellers– Ground Dwellers
Beak size varies with food type Stronger bill suited for seeds
– Warbler finch Insect eater in trees
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Examples of adaptive radiation
Ciscoes in Algonquin Park (11k yrs) Ancestor: Common Cisco Speciation beginning with ciscoes
developing specialized feeding apparatus: gill rakers to filter out different food types.
Photo: NOAA
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Mutation Rates Usually thought to be low in the absence of
mutagens (radiation, chemicals) Rates under “normal conditions”
– Humans: 0.5 to 25/100,000 gametes– Bacteria: 0.00007 to 0.41/100,000 gametes– But bacterial generations short! So adaptations
are fast. Most often mutations cause no visible
change
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Mutation & Adaptation in Use
Used in agriculture, industrial applications (pollution control, ore extraction, fermentation, etc).
Potato (Solanum tuberosum)– Now 500+ varieties
Corn (Zea mays)– Verities range from 0.6 to 6 m tall, 2-11
months to mature
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Genetic effects on Populations
Random drift:– With natural selection the most important cause
of evolution– Only some of the variation in parents passed on
to progeny– Imagine parents have few children, variation lost– Does not matter much if population is large– In small population effect is fast and significant
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Random drift Not limited to individuals that have
small populations Depends on chance events of flower
pollination, seed falling on suitable site, survival of fish or amphibian off spring (remember Nemo, only he survived out of 100!)
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Genetic bottlenecks Catastrophes, other chance events,
human activity sometimes reduce population dramatically– E.g. cheetahs population reduced a few
thousand years ago– Elephant seal: hunting: by 1890 20
individuals, today very limited genetic diversity.
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Founder effect Another type of genetic drift Caused when small population breaks
off and is reproductively isolated Founders genes only E.g. fruit flies on Pacific islands,
Icelandic cattle vs. Norwegian cattle
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Results Small populations can suffer from
inbreeding depression Depressed fitness (fertility and
survival, leading to low lifetime reproduction output)
Due to mating between close relatives
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Results Out breeding depression
– Fitness down after out crossing between genetically differentiated populations
– Example: planting same spp trees from different location: dilutes local genetic adaptation
– Ontario has seed zones to limit movement of tree seed on public lands
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Results Genetic swamping: a form of out
breeding depression Large amount of genetic material from
closely related spp introduced by humans
Rainbow troutCutthroat trout
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50/500 /5000Rule Soulé (1980) suggests: Need a population of at least 50 to avoid
short term in breeding Need 500+ to enable long term adaptability
and prevent reduction in evolutionary potential (prevent loss due to genetic drift)
Need 5000+ to serve as reservoir for future losses
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Genetic terms Gene: physical entities transmitted
from parent to offspring Genes made up two distinct types of
alleles Alleles=may be same or different
– E.g. allele for tall T or short t
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Genetic terms If alleles same: homozygous (TT or tt) If alleles different: heterozygous (Tt)
Locus= location– Position on a gene, may contain may
alleles
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Important features of genetic diversity
P = proportion of loci with more than 1 allele
A= No. of alleles at locus H = % of loci that are heterozygous Use electrophoresis to determine
these measures
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Use of genetic measures Used to determine relatedness E.g. found that salmon along E coast have high
allelic differences This means we should treat each river population
as separate management zones, not part of a metapopulation
25% of returning salmon in Norway from hatcheries Dilutes wild stock Keep hatchery fish from escaping Consider genetics when stocking
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Questions