Genetic diversity is the backbone of evolution

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Genetic diversity is the backbone of evolution !
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Why do we need diversity?The large picture

• Political demand for diversity
• Mans activities may lead to extinction of
  populations and species
• Mans influence seems to grow
• Man became most important ecological factor
  ?50000 years ago
• Diversity is the basis for evolution and thus life

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Man destroys biodiversity
Not long ago, giant wingless birds like this moa
paced New Zealand's open country and brushy
woodlands. Without large native predators to
threaten them, moas evolved to be the biggest
land predators on their island home.
But moas couldn't stand up to human
hunting Humans first reached New Zealand by canoe
about 1000 years ago. These settlers quickly
learned to hunt the defenceless moas. In fact,
they learned too well--in only about 700 years,
every last moa was gone.
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Biodiversity is appealing
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Evolution

• Diversity lost by selection and chance
• Diversity created by mutation
• Balance, population size 500 probably enough for
  sustainable diversity
• Forests much larger than that
• Forest tree breeding often operates with numbers
  larger than that (gt500)

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Numeric example

• The more A, the better'
• Ranking for A
• AAAAAA 6A
• AAAA 4A
• AAAA 4A
• AA 2A
• AA 2A
• AA 2A
• AA 2A
• A 1A
• The three top ranking has together only 8 A
• If all are selected the potential for 10 A
  remains
• Selecting best may mean missing something!

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Variance in sample
A sample need not be large to preserve the
variance of the original population!
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Rare alleles

• What alleles are rare?
• Almost all rare alleles are rather recent
  mutations and of no value
• Little recent advantage
• Most rare alleles in our forest trees will die
  away naturally.
• Even if they are of potential value, it is not
  easy to utilise rare alleles
• many generations to get effect
• in few initial genomes ? inbreeding problems if
  utilised,
• expensive screening to identify.

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• Mechanisms for important rare alleles
• balanced polymorphism?
• sometimes a little bad, sometimes very good?
• better if in low frequency.

A gene with a frequency of 10 is likely to be
conserved but a gene with frequency of 2 is
likely to be lost in a random mating population
of size 20.
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Limited impact of breeding

• Areas never regenerated on purpose,
• Natural regeneration 25,
• Natural volunteers in plantations,
• Pollen contamination (50 of pollen) in seed
  orchards.

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Unimproved
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Improved
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Diversity in a stand

• Genetic diversity in a stand is likely to favour
  biological production
• A single genotype demands the same things at the
  same time, bad site use!
• In a mix another genotype may take over the
  ecological space left by a failed genotype.
• A disease spreads faster in a uniform crop.
• This expectation has generally been confirmed by
  a number of experiments with different
  agricultural crops

 
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Too much diversity in plantations?!

• Most crop- and many forest managers do not like
  diversity,
• Uniform trees better economy, simpler
  management - even if biological production is
  lost,
• Genetic superiority of the best clones is much
  larger than the loss in biomass production by
  uniformity,
• The current demand for diversity in intensively
  managed forests is in my opinion - unreasonable
  expensive in lost future gain,
• Most of the benefits with diversity is obtained
  by five genotypes instead of an infinite number.

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Seed orchard crops are diverse!

• Phenotypic selection of plus trees are uncertain,
  preserves diversity,
• Marker gene measurements indicate that seed
  orchard crops can be more diverse than stand
  seeds!
• Seed orchard clones are recruited from a large
  area, which favours diversity compared to stands,
• Pollen sources outside the seed orchard favours
  diversity,
• Variances depends little on clonal number,
• In a small piece of a natural forest, trees are
  as related as trees from a seed orchard
  plantation.

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Measured with marker genes, most of the diversity
is within stands and little between stands, table
from (El-Kassaby 1991).   GST gives the share of
the genetic diversity that falls between stands.
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Reasons to consider gene diversity in breeding

• To boost breeding value when breeding population
  is creamed for production population,
• To obtain a production population with little
  inbreeding,
• To offer desirable gene diversity for production
  population (acceptability and production),
• To allow more aggressive breeding in the first
  cycles,
• To consume while accumulating additive effects,
• To keep inbreeding manageable in the breeding
  stock,
• To be prepared for changed emphasises,
• To combine breeding and gene conservation,
• Some intuitive feeling that diversity could be
  good to have,
• To demonstrate that breeders care for
  sustainability, breeding is not mining,
• A sense of respect,
• Genetic diversity is the basis for the
  professions forest geneticist and tree breeder.

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Too much diversity in breeding population?!

• Expensive
• In conflict with gain

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Extremest value increases slowly with number
The most extreme value of a population is raising
extremely slow as a function of population size,
thus to increase numbers is rather unefficient!
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Artificial selection is not a major short time
threat to diversity

• Low heritability conserved variance also after
  intensive phenotypic selection (gets worse when
  selection is on genotype instead of phenotype),
• 35000 genes interact to produce a phenotype. The
  influence of selection on the frequency of each
  gene must be small ,
• Selection for quantitative traits are likely to
  be selection for different genes at different
  selection occasions.

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Need of genetic diversity measure

• Demonstration that we care,
• For chiefs and "politicians" to demonstrate that
  they care,
• To monitor operations,
• To control operations,
• Review and compare different options for
  operations,
• Classify old and new forests, multiplication
  units, programs, development by time, diversity
  on stand, landscape, region and national level,
• Trade off with other quantifiable variables in
  the breeding system, like genetic gain, cost and
  time,
• Use for gene conservation purposes.

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Coancestry
Coancestry is the probability that genes taken at
random from each of a pair of individuals origin
from the same gene in a common ancestor.
Group coancestry is the probability that two
genes taken at random from a population origin
from the same gene in a common ancestor
(genomsnittligt släktskap)
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Group coancestry

• Average coancestry including self-coancestry
  (genomsnittligt släktskap)
• Loss of gene diversity group coancestry
• Group coancestry is a measure of gene diversity!

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Group coancestry and status number are useful as
diversity measures!
We need measures to control accumulation of
relatedness
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Interaction conservation and breeding
Gene conservation can be said to keep group
coancestry low Breeding should combine a high
gain and a reasonable group coancestry or Breeding
is much the art of balancing gain and group
coancestry
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Diversity changes at generation shifts because

• Drift (unavoidable),
• Balance of founder genes (can be optimised).