Conservation Genetics
Image of DNA double helix from Wikipedia
Conservation of Genetic Diversity
Image from www.tolweb.org
Conservation of Genetic Diversity
Evolution – allele frequency change through
time in a population
Some Mechanisms of Evolution
Mutation
Genetic accommodation – adaptive evolution
Random processes (e.g., genetic drift)
Gene flow via emigration & immigration
Artificial selection
Natural selection (Thank you, Darwin [& Wallace]!) – adaptive evolution
Sexual selection (Thank you, Darwin!) – adaptive evolution
Conservation of Genetic Diversity
Mutations (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
Gene flow – exchange of genes between populations
Pop. B
Pop. A
Genetic diversity erodes especially quickly
in small, isolated populations
Conservation of Genetic Diversity
Inbreeding – results from mating by closely related individuals
Pop. A
Generation 1
Pop. B
Generation 2
33% chance of mating with sibling
50% chance of mating with sibling
Genetic diversity erodes especially quickly
in small, isolated populations
Conservation of Genetic Diversity
Random processes (demographic bottlenecks,
genetic drift, founder effects)
Generation 1
Generation 2
Genetic diversity erodes especially quickly
in small, isolated populations
Conservation of Genetic Diversity
Not all phenotypic diversity results from genetic diversity
Genetic diversity helps determine evolutionary potential
R. A. Fisher
(1890 – 1962)
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"
Photo from Wikipedia
Conservation of Genetic Diversity
Genetic diversity occurs at 3 levels in a species’ gene pool:
Within individuals (e.g., heterozygosity – the proportion of gene loci in an
individual that contains alternative forms of alleles)
Among individuals in a population
Among populations
Conservation of Genetic Diversity
Genetic 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
Genetically effective population size (Ne) – 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  Ne < N
(Because of variance in reproductive success and family sizes)
Greater Yellowstone Ecosystem
grizzlies:
N ≈ 500
Ne ≈ 80
Image from www.time.com
Extinction Vortex
Small populations are at risk of
extinction owing to the “onetwo punch” from
demographics and
genetics
Image from Campbell & Reece (2008) Biology 8th ed., Benjamin Cummings Pubs.
Genetic Tools for Conservation
Pedigree 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
Case 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
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
12
50
8
4
0
0
1983
Figure from Vilà et al. (2003) Proc. R. Soc. Lond. B.
1991
2001
Number of breeding packs
Estimated population size
100
Case Study: Eurasian wolf
Vilà et al. (2003) Rescue of a severely bottlenecked wolf
(Canis lupus) population by a single immigrant
Individual heterozygosity
(19 autosomal microsatellite loci)
A single immigrant arrived onto the Scandinavian peninsula in 1991
Each circle = 1 wolf
1.0
Founding female
(est. date of birth =
1978)
Pups with d.o.b.
< 1991 (only 1
bottlenecked, inbred
pack)
0.5
Offspring of immigrant
male
Other pups with d.o.b.
 1991
0
1978
1983
Figure from Vilà et al. (2003) Proc. R. Soc. Lond. B.
1991
2001
Case 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
Case 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…”
f
1950
1960
1970
Figure from Adams et al. (2011) Proc. R. Soc. Lond. B.
1980
1990
2000
2010
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”
Figure from Johnson et al. (2010) Science