Download 2. Specific features for trees

Genetic erosion and pollution genetic and conservation consequences
for European forest tree species
François Lefèvre
INRA, Avignon (France)
Conclusion
Non-equilibrium paradigm for in situ management of long lived species
current
population size
genetic diversity
adaptedness
are not stable nor ideal quantities,
just instantaneous values resulting from dynamic processes
=> think in terms of parameter changes and evolutions
Conservation of genetic resources
Monitoring evolutionary changes
1. General concepts and
processes
2. Specific features for trees
3. Consequences for the
management of genetic
resources
1. General concepts and processes: genetic erosion
Ne, effective population size
a standardized measure of genetic evolution
(decrease of diversity or increase of inbreeding)
unit : size of a model population that follows the same genetic evolution
Ne = 30
Ne = 7
Ne = 
=>
constant Ne =>
Ne decreases =>
no evolution
stable evolution
erosion accelerates
1. General concepts and processes: genetic erosion
Departure from the model population that decreases Ne:
Biology
- true or partial dioecy
- departure from panmixia (both directions)
Demography
- variation in population size across generations
- variance (V) in mating success
- generation overlap
Environment
- selection
(Nunney, 2000)
human impact
1. General concepts and processes: hybridization-introgression
Hybridization (intra + interspecific)
Natural
Anthropogenic
Type 1
Natural
hybrid
Type 2
Natural
introgression
Type 3
Natural
hybrid zone
F1 only
(backcrosses)
Hybrid swarm
(sterile F1)
Type 4
Hybridization
no introgression
(Allendorf et al, 2001)
Type 5
Widespread
introgression
Type 6
Complete
admixture
1. General concepts and processes: balanced effects
demographic rescue
increase diversity
reduce inbreeding
restoration
risk of extinction  if :
(Lenormand, 2002)
demographic swamping
migration load
reduce Ne
extinction
local taxon is not rare
reproductive barriers are strong
long generation time
selfing or vegetative propagation
differencial selection is enhanced
2. Specific features for trees
2. Specific features for trees : high diversity
in spite of recent colonization history,
high diversity is generally maintained within tree populations
trees
annual
plants
nb species
mean nb pop.
mean nb loci
196
9.2
18.1
226
18.1
16.2
He (total div. )
Hs (within-pop div. )
Gst (differentiation)
0.177
0.148
0.084
0.154
0.101
0.355
(Hamrick et al, 1992)
2. Specific features for trees : local adaptation...
in spite of recent colonization history,
local adaptation rapidly developped through selection …
adaptive cline
in sessile oak
(Ducousso et al, 1996)
2. Specific features for trees : local adaptation & diversity
in spite of recent colonization history,
local adaptation rapidly developped through selection …
and high diversity for adaptive traits is maintained within tree-pops
h²
AGCV (sA/m %)
(Cornelius, 1993)
height
straightness
morphol. traits
wood density
branch
0.28
0.28
0.23
0.50
0.26
11.10
16.25
14.73
5.34
16.30
(Ducousso, unpubl.)
phenology
0.30
23.73
2. Specific features for trees : important gene flow
the high diversity is explained by important seed and pollen dispersal,
the long juvenile phase increases migration and reduces the founder
effect expected at founding a new deme
(Mariette, 2001)
(Austerlitz et al, 2000)
2. Specific features for trees : temporal patterns
erosion of diversity is delayed by temporal patterns of fecundity:
annual stochasticity reduces the impact of selection,
cumulative effect reduces drift
Ne=31
Ne=83
700
Ne=57
Ne=85
7743
Ne=36
2210
(Krouchi et al, 2004)
Ne=59
7822
Ne=92
Ne=76
398
584
7787
45719
2. Specific features for trees : adaptational lag
adaptation is a dynamic process where selection is balanced by
gene flow (migration load), interaction among species (Red Queen
hypothesis) and temporal fluctuations of environment
response function
142 pop Pinus contorta
tested on 60 sites
(Rehfeldt et al, 2001)
2. Specific features for trees : rapid adaptation
tree populations have the potential for rapid adaptive changes ...
% budset in
Norway spruce
date
(Skroppa & Kohman, 1997)
2. Specific features for trees : climate change
present tree populations and the next 1 or 2 generations will
experience climate change within their own life :
short
term
phenotypic plasticity
adaptation
long
term
migration
3. Consequences for management of genetic resources
3. Consequences for management: global perspective
Habitat
monitoring
Environmental
impact
Population
management
environment
landscape
wild
relative
interactions
domestic
resource
3. Consequence for management : genetic erosion
domestication (breeding and selection) :
 not a major threat for diversity in trees,
 except if low initial diversity
population management :
 direct impact on demographic parameters (life cycle,
dispersal, mating system, survival, mating success)
 should not affect the processes that maintain a high level
of diversity within tree populations
(Lefèvre, 2004)
3. Consequence for management : genetic pollution
introduction, fragmentation and habitat disturbance influence hybridization
risk assessment :
 assess hybridization, occurrence and frequency (difficult) ;
 estimate variation in frequency among cohorts ;
 estimate the relative fertility of local and hybrid types
reduce the impact of hybridization if considered as a risk :
 eliminate hybrids and invading sp ;
 improve habitat to enhance competition ;
(adapted from Wolf et al, 2001)
3. Consequence for management : genetic pollution
hypoth.: large amount of transplanted material involved in the regeneration
maladaptedness
local pop.
large Ne
genetic diversity
high
low
local pop.
small Ne
low
low
high
high
genetic diversity
high
low
maladaptedness can be avoided but low diversity more likely
higher impact when local population has small Ne
(Lefèvre, 2004)
Conclusion
Non-equilibrium paradigm for in situ management of long lived species
current
population size
genetic diversity
adaptedness
are not stable nor ideal quantities,
just instantaneous values resulting from dynamic processes
=> think in terms of parameter changes and evolutions
Conservation of genetic resources
Monitoring evolutionary changes
References
Allendorf et al, 2001
TREE
16, 613-622
Austerlitz et al, 2000
Genetics
154, 1309-1321
Cornelius, 1993
Can J For Res
24, 372-379
Ducousso et al, 1996
Ann Sci For
53, 775-782
Hamrick et al, 1992
New Forests
6, 95-124
Krouchi et al, 2004
For Ecol Manage 197, 181-189
Lefèvre, 2004
For Ecol Manage 197, 257-271
Lenormand, 2002
TREE
17, 183-189
Nunney, 2000
Evol Biol
32, 179-194
Rehfeldt et al, 2001
Climatic Change
50, 355-376
Skroppa & Kohman, 1997 Forest Genetics
4, 171-177
Wolf et al, 2001
15, 1039-1053
Conserv Biol