genetic diversity as a parameter for managing agroforestry systems
DESCRIPTION
A lecture about genetic diversity and its applications and importance for agroforestry systemsTRANSCRIPT
Genetic diversity as a parameter for managing agroforestry systems
Aristotelis C. PapageorgiouForest Genetics Laboratory
Democritus University of ThraceOrestiada, Greece
13/07/11 2
plan
- genetic diversity- changes of genetic diversity- genetic system in plant populations
• Agriculture• Rangeland• Forest
- management approach- examples / discussion
13/07/11 3
13/07/11 4
13/07/11 5
Important things about biodiversity Is of complex nature and finds its full meaning in
complex cases (e.g. landscapes and multiple levels of organization)
Involves different perceptions of its meaning and importance
13/07/11 6
Genetic component of biodiversity ...is a total of meaningless mathematic
expressions… Perlman & Adelson 1997
…should not be given priority, since its measurement is complicated and expensive… Dobson 1995
Misunderstandings: “Laboratory analysis is the first step of any gene
conservation or management measure” “The object of conservation and management
programmes are the genes we see in the laboratories”
13/07/11 7
So, what is genetic diversity? The differences among organisms that can be
inhereited Passing from one generation to the other = mating Changes over time = evolution
Is the basis of all other levels of biodiversity Underestimated and under-represented
Measured by: Field observations (environment? / P=G+E) Lab observations (practical relevance?
13/07/11 8
Field observations
- morphometry• Environmental or genetic?• Multivariable statistics• Landmarks
- common environment (trials)• Provenance / progeny tests• Traits of practical relevance
– Growth, survival, resistance...etc.• ANOVA
13/07/11 9
Lab observations
- previously: chromosomes, visible traits, enzymes- nowadays: polymorphism at DNA level
• Fragments (fragment length)• Sequencies of nucleotides• Some more sofisticated things...
- no direct relevance with traits• This changes however
- frequencies of genotypes and alleles
13/07/11 10
The population
- central concept to genetics- a set of individuals
• Mating (same species – or not?)• Same place (more or less)
- demography- frequency of alleles and genotypes
13/07/11 11
Alleles and genotypes
- allele: variant of the same gene that does the same job, just differently
• Mendel had yellow and green peas (gene = pea color / alleles = green and yellow)
• A diploid organism can have up to two different alleles at each gene
- genotype: the types of alleles at a gene• Homozygote: two copies of the same
allele• Heterozygote: two different alleles
13/07/11 12
Importance of genetic diversity Main condition for adaptation under new
environments Maintenance of populations and species Stability of communities and ecosystems Constant production of goods and services
Biological information base Is transferred over generations and rearranged
through mating system Influenced by population size Changes and promotes adaptation Is imported and exported
13/07/11 13
Evolution
Changes of allele or genotype frequencies over time and/or space
• Selection / adaptation• Small population size / genetic drift• Non-random mating / inbreeding• Migration / gene flow• Mutation
13/07/11 14
13/07/11 15
Selection
Some genotypes produce traits that have better chance to lead an organism to survive and reproduce
Higher fitnessThe alleles of this genotype pass easier to the next
generationGenotypes with greater fitness increase / so do their
allelesThe population is adapted to an environment
• Just until it changes...
13/07/11 16
13/07/11 17
Small population size
Not all individuals pass to the next generationNot all gametes successfully mateA fraction of the initial number of individuals (and
alleles) passes to the next generationReduction in numbers (randomly) changes allele
frequencies over time• Rare alleles are easier lost• Small populations lose their diversity
13/07/11 18
Ν=10000, p(A)=0,5
13/07/11 19
Ν=1000, p(A)=0,5
13/07/11 20
Ν=100, p(A)=0,5
13/07/11 21
Ν=20, p(A)=0,5
13/07/11 22
Genetic bottleneck
13/07/11 23
Fragmentation
13/07/11 24
Non random mating
Random mating• Equal probability of all mating events• Keeps frequencies of alleles and
genotypes stable• Equilibrium
Non random mating – inbreeding• Decreases heterozygotes• Increases the appearence of lethal genes• Inbreeding depression
13/07/11 25
Hedrick p. 183 up
13/07/11 26
Self – pollination / selfing
Most severe form of inbreeding• Results in full homozygosity in 6 / 7
generations• Reduces heterozygotes by 1/2 every
generation
In natural plant populations• Dissadvantage in outbreeding species• However, most species self pollinate• Evolutionary advantage under stable
environment– Stability of traits– Finall loss of lethal genes...
13/07/11 27
Plant breeding
The creation of new varietiesIn agriculture
• Self pollination creates “pure breeds”• Absolutely homozygous• Stable in artificial environment
In forestry• Self pollination is avoided• Reduces heterozygosity and fitness• More complex and variable environment
13/07/11 28
Migration – gene flow
Migration of individuals (seeds) or gametes (pollen)
• New alleles arrive aqnd increase diversity• Adaptation may be delayed
Ideal situation: small levels of gene flow allow diffrentiated adaptation and maintenance of high diversity levels
13/07/11 29
13/07/11 30
Lack of gene flow - fragmentation
13/07/11 31
Mutation
Primary source of variationNew allelesRare eventDoes not change frequencies of alleles
much
13/07/11 32
The genetic system of a forest
Genetic diversity is maintained when the genetic system is working!
13/07/11 33
In agriculture
Fields are ecosystems & production unitsFarming requires uniform conditions and uniform
material (one genotype)• Pure lines• Hybrids
How to increase genetic sustainability?• Change the scale!• See the broader picture• Use of local & adapted varieties• Uniformity in the field, not among fieldsI
13/07/11 34
In Forest Management
Natural populations on variable sites• Great diversity
Maintaining genetic diversity• Avoid disturbance of the genetic system• Use natural regeneration dynamics• Avoid fragmentation and small
populations• Proper / adapted reproductive material
See the broader picture• Manage at the landscape level
13/07/11 35
In rangelands and pastures
Natural ecosystems with large diversityUse natural dynamicsIntroduce proper material (local is safe)Avoid fragmentationAvoid overuse and degradationLandscape level
13/07/11 36
Agroforestry systems
Extensive, not intensive use of landLandscape level management
• Keep diversity within and – most important – among landscape elements and among landscapes
Maintain dynamics of nature• Natural cycles• Genetic system of plants
Avoid fragmentation – establish connectivityUse of proper plant material
• Adapted• Variable among units
13/07/11 37
Strategies
Forest management Secure pollen & seed movement Promote natural regeneration Expand management in non productive forests
– This includes rangelands Landscape connectivity Sustainable use of rangelands Improvement through proper material Restoration
Local seed or best adapted seed
13/07/11 38
New approach in forest management
13/07/11 39
Adaptive conservation & management
Ex situ: to preserve current genetic structures for future needs Frequent collection of reproductive material
for plant species Restore in gene banks Keep in plantations in different locations
Seed orchards for restoration purposes Adaptive breeding
13/07/11 40
Thank you