CONSERVATION BIOLOGY

advertisement
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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Metapopulations Reduce
Extinction Risk (I)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
• 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.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Population Viability Analysis (III)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
• 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
Download