Conservation Genetics:

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Chapter 11

• Conservation Genetics
• The use and importance of genetic information

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Genetics and Biodiversity

• Fundamental Theorem of Natural Selection (Fisher
  1930)
• Genes are the ultimate source of biodiversity
  (from Chapter 1)
• Genetic data helps resolve challenges in
  conservation

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Fundamental Theorem of Natural Selection

• Rate of evolutionary change proportional to
  amount of genetic diversity
• Genes provide raw materials for evolutionary
  potential
• Adapting to environmental conditions possible
  only with genetic variation

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Genes are Biodiversity

• Biological processes and products all linked to
  genes
• Loss of diversity decreases potential of
  sustaining biological processes in face of
  environmental changes
• Life blueprints valuable to humans may be lost

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Genes and conservation

• Evolutionary lineages focus conservation needs
• Identification of forces influencing diversity by
  comparing lineages and events
• Behaviors, migration with genetic basis important
  for conservation

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Conservation Genetics

• To help maintain natural patterns of genetic
  diversity at many levels
• Preserve options for future evolution
• To provide tools for population monitoring and
  assessment
• Tools to aid in conservation planning

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Genetic Variation

• The amount of genetic diversity within a species
• Three levels of species genetic variation
• Variation within individuals
• Genetic differences among individuals within a
  population
• Genetic differences among populations

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Individual variation

• Genes located on chromosomes in cell nuclei,
  mitochondria or chloroplasts
• Neutral genetic variation
• Heritable, but does not code for anything
• Natural selection does not operate here
• Adaptive genetic variation
• Heritable, codes for something
• Traits (and genes) subject to natural selection

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Individual variation

• Most often interested in adaptive
• Expression can be genetic, environmental, or both
  
• Two sources of new genetic material
• Mutation
• Recombination

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Review of Terms

• Locus
• Alleles
• Monomorphic vs polymorphic
• Homozygous vs heterozygous

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Variation among individuals

• Population-level variation
• The number of unique alleles and their
  frequencies
• Genetic diversity correlated with population size
• Large populations lose genetic diversity at
  slower rate than smaller populations

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Variation among populations

• Among-population divergence
• Species diversity the total genetic variability
  of all populations combined
• HT HP DPT
• HT total genetic variation
• HP average diversity within population
• DPT avg divergence among populations

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Metapopulations

• Distinct populations that are relatively
  independent but are connected through individual
  movements and gene flow
• Each population is then considered part of a
  larger population
• Extinction events occur along with recolonization
  events

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Metapopulations

• Persist for longer duration than stand-alone
  populations
• Small number of individuals leads to
• Genetic diversity lower within populations
• Loss of genetic variation more rapid

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When is a population a metapopulation?
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Why is genetic diversity important?
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Effective Population Size (Ne)

• Genetically effective population size
• Size of an idealized population that would have
  the same inbreeding, loss of heterozygosity,
  genetic drift
• The Ne generates more accurate picture of forces
  influencing genetic diversity within the actual
  population

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Forces affecting Genetic Variation

• Mutation
• Genetic drift
• Gene flow
• Inbreeding depression
• Outbreeding depression
• Natural selection

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Mutation

• Errors in replication or alteration of the genome
  are source of new genetic variation
• Low rates of occurrence mean weight of mutation
  measured over evolutionary time
• Usually neutral, but can have deleterious, or
  negative, effects

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Mutation

• Probability of extinction may be affected by
  deleterious mutations
• Fixation
• All individuals in a population are homozygous
  for the mutation
• Large populations have low probabilities of
  fixation

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Genetic drift

• Random fluctuation of gene frequencies over time
  due to chance
• Expect alleles to occur in future generations as
  their frequency today
• Small populations experience loss of alleles at
  higher rates

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Genetic drift

• End result of genetic drift is that only one
  allele survives
• Direction of genetic drift is random
• Conservation implications
• Closed populations only have mutation as source
  of new genetic material
• Maintaining large populations and connectivity of
  populations important in minimizing effects of
  genetic drift

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Gene flow

• The movement of genes from one population to
  another, via individuals
• Gene flow difficult to measure
• Can combat negative effects of genetic drift

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Genetic drift vs Gene flow

• Process of each balances effects of the other
• Gene flow tends to homogenize populations and
  combat genetic drift
• Genetic drift can increase variation among
  populations given enough isolation

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Inbreeding depression

• Reduced fitness due to the homozygous expression
  of deleterious alleles or the overall loss of
  heterozygosity
• No change in allele frequency, but an increase in
  homozygous state
• Small, isolated populations more likely to
  experience intense inbreeding depression

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Outbreeding depression

• The opposite of inbreeding depression
• Negative effects on fitness due to increased
  heterozygous occurrence from breeding between
  very different individuals
• Extreme result is lack of fertile or viable
  offspring, if fertilization occurs at all

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Natural Selection

• Differential survival and reproduction of
  different genotypes in a population, OR
• Differential success of genotypes passing gametes
  into the next generation
• Selection components
• Viability
• Sexual
• Fertility

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Natural Selection

• Some alleles offer greater fitness than others
• Three outcomes for diallelic loci
• Homozygous more advantageous
• More common allele becomes more dominant
• Heterozygous inferior
• Overdominance
• Heterozygous superiority

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Forces affecting Genetic Variation

• Mutation
• Genetic drift
• Gene flow
• Inbreeding depression
• Outbreeding depression
• Natural selection

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Under ESA, a species is

• Any subspecies and any distinct population
  segment of vertebrate of wildlife.

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Evolutionary Significant Unit (ESU)

• Identifies a population as distinct under ESA
• Two criteria
• Substantially reproductively isolated from
  conspecific population units
• Represent an important component in the
  evolutionary legacy of the species

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DNA barcodes

• Identifies species based on short sequence (648
  base pairs) of mitochondrial DNA (COI)

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DNA barcodes

• Advantages
• Faster process and inexpensive
• Standardized region for most animals
• Mitochondrial DNA has greater variation
• Concerns
• Degree of difference somewhat arbitrary
• Use of mitochondrial DNA only may not recognize
  differences for hybrids

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Strategies for Conserving Species
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Should conservation focus more on genes and
genetic variation?

• Less focus on populations, species, and
  communities?

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Genetics in Conservation

• Lack of access to genetic tools and knowledge of
  methodologies
• Maintenance of plant and animal tissues requires
  freezers and other equipment
• Knowledge of genetic relatedness and variation
  does not resolve other threats to biodiversity

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Pop Quiz
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This term refers to the quantity and frequency of
invading individuals, and includes the ability of
the invading population to overcome the negative
effects of an initially small population.

• Greenhouse effect
• Enemy release
• Propagule pressure

• D. Allee effect
• E. Metapopulations