CONSERVATION GENETICS

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CONSERVATION GENETICS

• READINGSFREEMAN, 2005
• Chapter 52
• 1206-1210
• Chapter 54Pages 1272-1277

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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
• Morphological variation -- a good clue, but does
  not correlate perfectly with genetics
• Chromosomal variation -- inversions,
  translocations and polyploidy
• Soluble proteins -- blood groups, soluble enzyme
  polymorphisms
• DNA markers -- microsatellites, fingerprint
  loci.

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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.

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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 1990s.

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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.

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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.

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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).

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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.

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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.

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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.

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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 NF
• where NM number of males
• NF number of females

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Effective Population Size (Ne)

• What is the effective population size (Ne) of one
  with 100 females and 10 males?
• Remember
• Ne 4(NM NF)
• NM NF
• where NM number of males
• NF number of females

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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)
• NM NF
• where NM number of males
• NF number of females

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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 (individuals).
• Least likely in large populations (individuals.

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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

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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

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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

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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

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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 _________ 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

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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.

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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)

• Studies of the Granville fritillary show how
  subpopulations stabilize overall population size.
• In addition, provide opportunity for gene flow.

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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.

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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.

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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 .

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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.

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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).

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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.

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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.

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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.

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LIFE HISTORY TRAITS FORM A CONTINUUM (III)

• See Freeman (2005) page 1195 for full discussion.

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Some Long Lived Species
Whooping Crane
Spotted Owl

• These have moderate juvenile mortality, low adult
  mortality, and low fecundity.
• They are endangered.

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Some Short Lived Species
Starling
House Finch

• These have high juvenile mortality, moderate
  adult mortality, and high fecundity.
• They are thriving.

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CONSERVATION GENETICS

• READINGSFREEMAN, 2005
• Chapter 52
• 1206-1210
• Chapter 54Pages 1272-1277