Image from wwwtolweborg Conservation of Genetic Diversity Image from wwwtolweborg Conservation of Genetic Diversity Some Mechanisms of Evolution Mutation Genetic accommodation adaptive evolution ID: 911173
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Slide1
Conservation Genetics
Image of DNA double helix from Wikipedia
Slide2Image from www.tolweb.org
Conservation of Genetic Diversity
Slide3Image from www.tolweb.org
Conservation of Genetic Diversity
Slide4Some Mechanisms of Evolution
Mutation
Genetic accommodation
– adaptive evolution
Random processes (e.g., genetic drift)Gene flow via emigration & immigrationArtificial selectionNatural selection (Thank you, Darwin [& Wallace]!) – adaptive evolutionSexual selection (Thank you, Darwin!) – adaptive evolution
Evolution
– allele frequency change through
time in a population
Conservation of Genetic Diversity
Slide5Mutations (substitutions, insertions, deletions, inversions)
– ultimate sources of most genetic variation
Generation 1
Generation 2
Small populations provide few opportunities
for positive mutations to arise
Conservation of Genetic Diversity
Slide6Gene flow
– exchange of genes between populations
Genetic diversity erodes especially quickly
in small, isolated populations
Pop. A
Pop. B
Conservation of Genetic Diversity
Slide7Inbreeding
– results from mating by closely related individuals
Genetic diversity erodes especially quickly
in small, isolated populations
Generation 1
Generation 2
Pop. A
Pop. B
33% chance of mating with sibling
50% chance of mating with sibling
Conservation of Genetic Diversity
Slide8Genetic diversity erodes especially quickly
in small, isolated populations
Random processes (demographic bottlenecks,
genetic drift, founder effects)
Generation 1
Generation 2
Conservation of Genetic Diversity
Slide9Photo from Wikipedia
Not all phenotypic diversity results from genetic diversity
Genetic diversity helps determine evolutionary potential
An architect
of the
Modern Synthesis
Fisher’s Fundamental Theorem: "The rate of increase in fitness [
owing to selection
] of any organism at any time is equal to its genetic variance in fitness at that time"
R. A. Fisher
(1890 – 1962)
Conservation of Genetic Diversity
Slide10Genetic diversity occurs at 3 levels in a species’
gene pool
:
Within individuals (
e.g.
,
heterozygosity
– the proportion of gene loci in an individual that contain alternative forms of alleles)
Among individuals in a population
Among populations
Conservation of Genetic Diversity
Slide11Genetic diversity helps determine evolutionary potential
But, “
gene pools
are becoming diminished and fragmented
into
gene puddles
” (Foose 1983)
Image from www.brooklyn.cuny.edu
Conservation of Genetic Diversity
Slide12Genetically effective population size (N
e
)
– the number of individuals that would result in the same level of inbreeding, or decrease in genetic diversity through time, if the population were an idealized,
panmictic (randomly mating) population
Typically
N
e
< N
(Because of variance in reproductive success and family sizes)
Image from www.time.com
Greater Yellowstone Ecosystem grizzlies:
N ≈ 500
N
e
≈ 80
Conservation of Genetic Diversity
Slide13Genetically effective population size (N
e
)
– the number of individuals that would result in the same level of inbreeding, or decrease in genetic diversity through time, if the population were an idealized,
panmictic (randomly mating) population
Typically
N
e
< N
(Because of variance in reproductive success and family sizes)
Conservation of Genetic Diversity
Generation 1:
♀
♂ ♀
♂
♀
♂ ♀ ♂ ♀ ♂
Generation 2: ♀ ♂ ♀ ♂ ♀ ♂ ♀ ♂ ♀ ♂
Slide14Image from Campbell & Reece (2008) Biology 8
th
ed., Benjamin Cummings Pubs.
Small populations are at risk of extinction owing to the “one-two punch” from demographics and
genetics
Extinction Vortex
Slide15Pedigree analysis – especially useful for captive populations
Estimation of relatedness (in the absence of pedigrees)
Analysis of parentage and mating systems
Forensics
Species or population identification
Estimation of population size
Image of elephant ivory from www.guardian.co.uk
Genetic Tools for Conservation
Slide16Case Study: Eurasian wolf
Vilà
et al
. (2003) Rescue of a severely bottlenecked wolf
(Canis lupus) population by a single immigrant
“We show here that the
genetic diversity
of the
severely bottlenecked
and
geographically isolated
Scandinavian population of grey wolves
(
Canis lupus),
founded
by only two individuals [in 1983, after centuries of
persecution that extirpated them from the Scandinavian peninsula by 1960s],
was recovered by the arrival of a
single immigrant
.”
Quote from Vilà
et al
. (2003)
Proc. R. Soc. Lond. B.
; photo & map of Europe from Wikipedia
Slide17Figure from Vilà
et al
. (2003)
Proc. R. Soc. Lond. B.
Case Study: Eurasian wolf
Vilà
et al
. (2003) Rescue of a severely bottlenecked wolf
(
Canis lupus
) population by a single immigrant
A single immigrant arrived onto the Scandinavian peninsula in 1991
1983
1991
2001
Estimated population size
Number of breeding packs
0
50
100
0
4
8
12
Slide18Figure from Vilà
et al
. (2003)
Proc. R. Soc. Lond. B.
Case Study: Eurasian wolf
Vilà
et al
. (2003) Rescue of a severely bottlenecked wolf
(
Canis lupus
) population by a single immigrant
A single immigrant arrived onto the Scandinavian peninsula in 1991
1983
1991
2001
Individual heterozygosity
(19 autosomal microsatellite loci)
1978
Each circle = 1 wolf
0
0.5
1.0
Founding female
(est. date of birth = 1978)
Pups with d.o.b.
< 1991 (only 1 bottlenecked, inbred pack)
Offspring of immigrant male
Other pups with d.o.b.
1991
Slide19Case Study: North American wolf
Adams
et al
. (2011) Genomic sweep and potential genetic rescue during limiting environmental conditions in an isolated wolf population
“…a male wolf (
Canis lupus
)… immigrated [in 1997]… across Lake Superior ice to the small, inbred wolf population in Isle Royale National Park. The immigrant’s fitness so exceeded that of native wolves that within 2.5 generations he was related to every individual in the population… resulting in a selective sweep of the total genome.”
Quote & photo from Adams
et al
. (2011)
Proc. R. Soc. Lond. B.
; map of North America from Wikipedia
Slide20Case Study: North American wolf
Adams
et al
. (2011) Genomic sweep and potential genetic rescue during limiting environmental conditions in an isolated wolf population
“The population inbreeding coefficient (
f
) averaged over each
individual present in the population from 1950 to 2009...
Our results show that the beneficial effects of gene flow
may be substantial and quickly manifest…”
Figure from Adams
et al
. (2011)
Proc. R. Soc. Lond. B.
1950
1960
1970
1980
1990
2000
2010
f
Slide21Figure from Johnson
et al
. (2010)
Science
Case Study: Florida panther
Johnson
et al
. (2010) Genetic restoration of the
Florida panther (
Puma concolor coryi
)
Eight females were translocated from Texas to Florida in 1995; “panther numbers increased threefold, genetic heterozygosity doubled, survival and fitness measures improved, and inbreeding correlates declined significantly”
Slide22