Testing for rapid adaptation
in fireweed
Andrew Lowe, Eleanor Dormontt, Peter Prentis
Australian Centre for Evolutionary Biology and Biodiversity
School of Earth & Environmental Sciences
The University of Adelaide
28th May 2008
A sleeper weed
• Lag phase between introduction and
population explosion, may last generations
• Range of ecological explanations
– Demographic population increase
– Release from native predators/herbivores
– Change in climate – more suitable
A sleeper weed
• Lag phase between introduction and
population explosion, may last generations
• Range of ecological explanations
– Demographic population increase
– Release from native predators/herbivores
– Change in climate – more suitable
– Genetic explanations for post introduction
adaptation – well known in evolutionary
biology but rarely considered for weeds
– Prentis, Wilson, Dormontt, Richardson, Lowe (2008) TIPS
Genetic mechanisms of adaptation
1.
2.
3.
4.
Bottleneck
Admixture – multiple sources
Hybridisation
Gene expression and genome selection
Genetic mechanisms of adaptation
1.
2.
3.
4.
Bottleneck
Admixture – multiple sources
Hybridisation
Gene expression and genome selection
ARC Discovery funded
– Elly Dormontt – PhD
– Peter Prentis & Skye Thomas Hall - Postdocs
Genetic mechanisms of adaptation
1. Bottleneck
– mating system, genetic diversity
2. Admixture
– source of introduction
3. Hybridisation
– introgression and demographic swamping
4. Gene expression and genome selection
– Dynamics and rapid evolution of species
Cumulative number of herbarium records
Spread dynamics
250
200
150
Population "explosion"
(Sindel & Michael 1988)
•1918 Hunter Valley
100
End of lag phase
(sensu Pyšek & Prach 1993)
50
0
1918
1928
1938
1948
1958
1968
Year
1978
1988
1998
2008
Spread dynamics
1948
Spread dynamics
1968
Spread dynamics
1988
Spread dynamics
2008
Spread dynamics
100
90
80
70
cumulative number of herbarium records
√ cumualative area
Σ north + south extent
%
60
50
40
30
20
10
0
1918
1928
1938
1948
1958
1968
Year
1978
1988
1998
2008
Spread dynamics
100
90
80
70
cumulative number of herbarium records
√ cumualative area
Σ north + south extent
%
60
50
40
Population boom
circa 1983
post drought
30
20
10
0
1918
1928
1938
1948
1958
1968
Year
1978
1988
1998
2008
Genetic mechanisms of adaptation
1. Bottleneck
– mating system, genetic diversity
2. Admixture
– source of introduction
3. Hybridisation
– introgression and demographic swamping
4. Gene expression and genome selection
– Dynamics and rapid evolution of species
Genetic mechanisms of adaptation
1. Bottleneck
– mating system, genetic diversity
2. Admixture
– source of introduction
3. Hybridisation
– introgression and demographic swamping
4. Gene expression and genome selection
– Dynamics and rapid evolution of species
Bottlenecks
• Traditionally thought to constrain adaptation
– Reduced quantitative variation
• Under extreme inbreeding can get new
genetic variants (hopeful monsters)
– May allow adaptation to new environments
Bottlenecks
• Traditionally thought to constrain adaptation
– Reduced quantitative variation
• Under extreme inbreeding can get new
genetic variants (hopeful monsters)
– May allow adaptation to new environments
• Invasive Canary Island St John’s wort
– Extreme bottleneck – locally adapted populations
Bottlenecks
• Unlikely for fireweed
• Mating system is outcrossing
– biparental inbreeding
– (Prentis et al 2007 New Phytologist)
• High genetic variation in Hawaiian populations
– Sourced from Australia (Le Roux 2008 Div&Dist)
Bottlenecks
• Unlikely for fireweed
• Mating system is outcrossing
– biparental inbreeding
– (Prentis et al 2007 New Phytologist)
• High genetic variation in Hawaiian populations
– Sourced from Australia (Le Roux 2008 Div&Dist)
• Does not rule out bottleneck during early stages of
Australian colonisation
• Will genetically screen contemporary populations and
herbarium specimens – bottlenecks, mating system
Genetic mechanisms of adaptation
1. Bottleneck
– mating system, genetic diversity
2. Admixture
– source of introduction
3. Hybridisation
– introgression and demographic swamping
4. Gene expression and genome selection
– Dynamics and rapid evolution of species
Admixture
Novel gene combinations
Admixture
Earlier genetic work by Radford and Scott et al
indicate that Kwa-Zulu Natal is the likely source
region of introduction for fireweed into Australia
Admixture
Kwa-Zulu Natal
Conducting microsatellite analysis
of dynamics of source
introductions
East coast Australia
Admixture
Kwa-Zulu Natal
Single source
Similar studies now done on range of
species
Scotch broom, cats claw, bellyache bush
East coast Australia
Admixture
Kwa-Zulu Natal
Multiple sources East coast Australia
Similar studies now done on range of
species
Scotch broom, cats claw, bellyache bush
Admixture
Kwa-Zulu Natal
Multiple sources
temporal spread East coast Australia
Analysis of contemporary populations and
herbarium specimens to track introduction history
Genetic mechanisms of adaptation
1. Bottleneck
– mating system, genetic diversity
2. Admixture
– source of introduction
3. Hybridisation
– introgression and demographic swamping
4. Gene expression and genome selection
– Dynamics and rapid evolution of species
Hybridisation
multiple outcomes
Invasive
Native
Extinction
e.g. Mercurialis annua
Introgression
Speciation
e.g. Helianthus
annuus ssp. texanus
e.g. Senecio squalidus
Hybridisation
• Hybridisation
– Sample collections from hybrid zones with S. pinnatifolius
Involucral
bracts
18-21 = Senecio madagascariensis (Fireweed)
11-14 = Senecio pinnatifolius
Hybridisation
• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid
capitula
native
seed
invasive
seed
Hybridisation
• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
S. pinnatifolius (native)
S. madagascariensis (invasive)
Undue influence by fireweed on
level of hybridisation in native
-asymmetric hybridisation
Hybrid
capitula
native
seed
invasive
seed
Hybridisation
• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
S. pinnatifolius (native)
S. madagascariensis (invasive)
No viable hybrids found at field site,
hybrids are not developing and are
therefore gamete sink
Hybrid
capitula
native
seed
invasive
seed
Hybridisation
• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
S.
pinnatifolius
S.
madagascariensis
Total seed (plant)
505
422
Post germination
338
304
Post
establishment
274
252
Hybridisation
(20% fireweed)
225
245
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid
capitula
native
seed
invasive
seed
Hybridisation
• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid
capitula
native
seed
invasive
seed
Hybridisation
multiple outcomes
Invasive
Native
Extinction
Introgression
Speciation
Hybridisation
• Mature hybrids found
between fireweed and
dune variant
• Unknown hybrid outcome
with headland variant
• 3 sympatric sites sampled
– Genetic analysis underway
• Examine role of hybrids in
history – herbarium survey
Genetic mechanisms of adaptation
1. Bottleneck
– mating system, genetic diversity
2. Admixture
– source of introduction
3. Hybridisation
– introgression and demographic swamping
4. Gene expression and genome selection
– Dynamics and rapid evolution of species
Gene expression and selection
Experimental strategy
Landscape genomics
Genetic maps
Expressed genes isolated
Quantification of which genes
have changed expression source (South Africa) and
introduction (Australia)
Candidate genes are
screened for variation
and evidence for
genome selection
Range of
variable genes
under selection
‘Weedy genes’
Summary of key findings
•
•
•
•
Mating system and population dynamics
Source of introduction – biocontrol source
History of introduction and mixing
Dynamics of hybridisation
– Demographic swamping and/or introgression
• Gene expression and genome selection
– Selective response due to environment
– Weedy genes, rapid adaptation and evolution
Acknowledgements
Drs Peer Schenk (UQ) and Tony Clarke (QUT)
Prof Dave Richardson and Dr John Wilson (Stellenbosch, South Africa)
Profs Richard Abbott (St Andrews, UK) and Loren Rieseberg (UBC)