CONSERVATION GENETICS
READINGS:
FREEMAN, 2005
Chapter 52
1206-1210
Chapter 54
Pages 1272-1277
GENETIC DIVERSITY
The diversity of life is fundamentally genetic. A
variety of genetic methods have been used
to investigate diversity both within and
between species. Here are a few:
1. Morphological variation -- a good clue, but
does not correlate perfectly with genetics;
2. Chromosomal variation -- inversions,
translocations and polyploidy;
3. Soluble proteins -- blood groups, soluble
enzyme polymorphism’s;
4. DNA markers -- microsatellites, “fingerprint”
loci.
CONSERVATION OF
GENETIC VARIATION
• The foundation of diversity is the process of
natural selection shaping genetic variation.
• When genetic variation is absent (zero
heterozygosity), the population (or species)
has limited evolutionary potential and the risk
of extinction is high.
• The conservation of genetic variation
provides a hedge against extinction.
An Endangered Species: Red Wolf
• This canine family
member was once
found in the
southeast. It
disappeared in the
wild by the late
1970s.
• Reintroduced into
Great Smoky
Mountains National
Park in 1990’s.
An Endangered Species: Red Wolf
• Examination of DNA
demonstrated that the
red wolf is a hybrid
between gray wolf and
coyote.
• Expansion of coyote
range and shrinking of
gray wolf range resulted
in gene swamping of
red wolf genes by
coyote genes.
An Endangered Species: Cheetah
• A species that shows a
very low level of genetic
variation.
• May have experienced a
genetic bottleneck near
the end of the last ice age
(10,000 - 12,000 years
ago) when many other
mammal species became
extinct.
• Low genetic variation in
“fingerprint” loci compared
to other cat species.
Population Size and Extinction
Risk
• Populations are subject to chance or
sampling error in getting alleles from one
generation to the next (genetic drift, genetic
bottlenecks, founder effects).
• Populations are subject reduction in gene
flow and gene swamping.
• Small populations are particularly vulnerable
to extinction due to reduction in genetic
variation (heterozygosity).
CONSERVATION GENETICS (I)
• Conservation genetics is an area of study that
determines genetic variation and the
processes that diminish it.
• Heterozygosity is a measure of genetic
variation.
• Processes that diminish heterozygosity,
especially in small populations, are: 1)
genetic drift; 2) genetic bottlenecks; 3)
inbreeding.
CONSERVATION GENETICS (II)
• The movement of alleles from one population
to another is called gene flow.
• Gene flow promotes heterozygosity by
increasing the chances of outbreeding.
• Fragmentation often results in a reduction of
gene flow into isolated populations.
• Gene swamping occurs when small
populations are genetically assimilated by
much larger populations.
Effective Population Size (Ne)
• Effective population size gives a crude
estimate of the average number of
contributors to the next generation (Ne).
• Always a fraction of the total population.
• Some individuals will not produce
offspring due to age, sterility, etc.
• Of those that do, the number of progeny
many vary.
Effective Population Size (Ne)
• A variety of ways of estimating (Ne)
have been formulated.
• One that accounts for unequal sex
ratios among breeding adults is:
Ne = 4(NM * NF)
NM + N F
where NM = number of males
NF = number of females
Effective Population Size (Ne)
• What is the effective population size (Ne) of one
with 100 females and 10 males?
• Remember:
Ne = 4(NM * NF)
N M + NF
where NM = number of males
NF = number of females
Effective Population Size (Ne)
• What is the effective population size (Ne) of one
with 100 females and 10 males?
Ne = 4(100 * 10) = 4000 = 36
100 + 10
110
• Remember:
Ne = 4(NM * NF)
N M + NF
where NM = number of males
NF = number of females
Genetic Drift
• Random change in allele frequency due
to sampling only a small portion of
gametes from the previous generation.
• Most likely in small populations (<100
individuals).
• Least likely in large populations (<
1,000 individuals.
Genetic Drift
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Genetic Drift
The proportion of genetic variation
retained in a population of constant size
after t generations is approximately:
Proportion = (1 -1/(2N))t
where N = number of individuals
t = number of generations
Genetic Drift
What proportion of genetic variation is
retained in a population of 10 individuals
after 10 generations?
Proportion = (1 - 1/20)10 = 0.9510
= .5987 or about 60%
Proportion = ((1 -1/(2N))t
where N = number of individuals
t = number of generations
Genetic Bottleneck
• The loss of genetic variation when a
population drops in size.
• Effective population size (Ne) after a
fluctuation in population size is estimated by:
Ne = t/ sum of (1/Ni)
where Ni = size of population in generation i
t = number of generations
Genetic Bottleneck
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Genetic Bottleneck
What is the effective population size (Ne) of one
that goes from 1,000 (t1) to 10 (t2) and
recovers to 2,000 (t3)?
Ne = t/ sum of (1/Ni)
where Ni = size of population in generation i
t = number of generations
Genetic Bottleneck
What is the effective population size (Ne) of one
that goes from 1,000 (t1) to 10 (t2) and
recovers to 2,000 (t3)?
Ne = _________ 3 ________ = 3/0.1015
1/1000 + 1/10 + 1/2000
= 29 individuals
Ne = t/ sum of (1/Ni)
where Ni = size of population in generation i
t = number of generations
Inbreeding
• Inbreeding occurs more frequently in isolated
and small populations.
• It acts to reduce Ne. It is estimated bY;
Ne. = ____N_____
1 + F
where F is the inbreeding coefficient
or probability of inheriting 2 alleles
from the same ancestor.
Inbreeding vs Outbreeding
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Inbreeding Depression
• Prairie chickens in
Illinois declined due
to decreased
hatching success.
• Individuals from
Iowa were
introduced to the
breeding population
and hatching
success improved.
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Metapopulations Reduce
Extinction Risk (I)
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• Studies of the
Granville fritillary
show how
subpopulations
stabilize overall
population size.
• In addition, provide
opportunity for gene
flow.
Metapopulations Reduce
Extinction Risk (I)
• Oerall population size
remains relatively stable
even when local
populations go extinct.
• The metapopulation
provided for increased
opportunity for gene flow
between local
populations.
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Population Viability Analysis (I)
• PVA provides a means for estimating the
likelihood that a population will avoid
extinction for a given period of time.
• Freeman (2005) describes a study of how
migration rates are likely to influence
population viability of an endangered
marsupial.
Population Viability Analysis (II)
• This endangered
marsupial lives in an
old-growth forest in
southeastern Australia
and relies on dead trees
for nest sites.
• PVA was used to predict
the consequences of
habitat loss and forest
fragmentation on this
endangered species.
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Population Viability Analysis (III)
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Population Viability Analysis
• Freeman describes demographic studies of a
European lizard species that is declining in
some areas.
• He explains how migration maintains some
local populations in spite of local extinction.
• He presents a model of how migration rates
are likely to influence population viability of an
endangered marsupial.
Life History Characteristics,
Population Size and Extinction
Risk
• Extinction risk is related to the life
history characteristics of the species in
question.
• Small populations with “long-lived” life
history characteristics are particularly
vulnerable to extinction .
LIFE HISTORY
CHARACTERISTICS
• Population attributes such as lifespan,
mortality and natality patterns, biotic
potentials, and patterns of population
dynamics are called life history
characteristics.
• Life history characteristics have
important consequences for wildlife
management and extinction risk.
FOUR IMPORTANT
ASPECTS OF LIFE
HISTORIES
• 1. Lifespan --- the upper age limit for the
species.
• 2. Mortality --- the pattern of survivorship (I,
II, or III).
• 3. Natality --- the age to reproductive
maturity and number of offspring produced.
• 4. Biotic potential --- maximum rate of
natural increase (rmax = births - deaths).
LIFE HISTORY EXTREMES
• Short-lived.
• Type III survivorship
high juvenile mortality;
relatively secure old
age.
• Many offspring from
young adults.
• High maximum rate of
population growth.
• Long-lived.
• Type I survivorship:
low juvenile mortality;
high mortality at old
age.
• Few offspring from
older adults.
• Low maximum rate of
population growth.
LIFE HISTORY TRAITS
FORM A CONTINUUM (I)
• Every species can be placed
somewhere on a continuum with
respect to the life history extremes.
• Comparisons of life histories are
best done between species that
show similar evolutionary histories.
LIFE HISTORY TRAITS
FORM A CONTINUUM (II)
• Field mice and muskrats
are rodents in closely
related taxonomic families.
• Field mice (short-lived)
show a
Type III survivorship and
produce many offspring.
• Muskrats (long-lived) have
a Type I survivorship and
produce few young.
LIFE HISTORY TRAITS
FORM A CONTINUUM (III)
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• See Freeman (2005) page 1195 for full
discussion.
Some Long Lived Species
Whooping Crane
Spotted Owl
• These have moderate juvenile mortality, low
adult mortality, and low fecundity.
• They are endangered.
Some Short Lived Species
Starling
House
• These have high juvenile mortality,Finch
moderate adult
mortality, and high fecundity.
• They are thriving.
CONSERVATION GENETICS
READINGS:
FREEMAN, 2005
Chapter 52
1206-1210
Chapter 54
Pages 1272-1277