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. Bottleneck
2. Admixture – multiple sources
3. Hybridisation
4. Gene expression and genome selection
Genetic mechanisms of adaptation
1. Bottleneck
2. Admixture – multiple sources
3. Hybridisation
4. 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
Spread dynamics
0
50
100
150
200
250
1918 1928 1938 1948 1958 1968 1978 1988 1998 2008
Year
Cu
mu
lati
ve
nu
mb
er
of
he
rba
riu
m r
ec
ord
s
Population "explosion" (Sindel & Michael 1988)
End of lag phase (sensu Pyšek & Prach 1993)
•1918 Hunter Valley
Spread dynamics
1948
Spread dynamics
1968
Spread dynamics
1988
Spread dynamics
2008
Spread dynamics
0
10
20
30
40
50
60
70
80
90
100
1918 1928 1938 1948 1958 1968 1978 1988 1998 2008
Year
%
cumulative number of herbarium records√ cumualative areaΣ north + south extent
Spread dynamics
0
10
20
30
40
50
60
70
80
90
100
1918 1928 1938 1948 1958 1968 1978 1988 1998 2008
Year
%
cumulative number of herbarium records√ cumualative areaΣ north + south extent
Population boom circa 1983 post drought
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
AdmixtureKwa-Zulu Natal East coast Australia
Conducting microsatellite analysis of dynamics of source introductions
AdmixtureKwa-Zulu Natal East coast Australia
Similar studies now done on range of speciesScotch broom, cats claw, bellyache bush
Single source
AdmixtureKwa-Zulu Natal East coast AustraliaMultiple sources
Similar studies now done on range of speciesScotch broom, cats claw, bellyache bush
AdmixtureKwa-Zulu Natal East coast Australia
Analysis of contemporary populations and herbarium specimens to track introduction history
Multiple sourcestemporal spread
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
Introgression
e.g. Helianthus annuus ssp. texanus
Speciation
e.g. Senecio squalidus
Extinction
e.g. Mercurialis annua
Invasive Native
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)
capitulanative seed
invasive seed
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid
Hybridisation• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
capitulanative seed
invasive seed
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid Undue influence by fireweed onlevel of hybridisation in native-asymmetric hybridisation
Hybridisation• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
capitulanative seed
invasive seed
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid No viable hybrids found at field site,hybrids are not developing and aretherefore gamete sink
Hybridisation
capitulanative seed
invasive seed
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid
S. pinnatifolius
S. madagascariensis
Total seed (plant) 505 422
Post germination 338 304
Post establishment
274 252
Hybridisation (20% fireweed)
225 245
• S. pinnatifolius Springbrook tableland variant (Prentis et al, New Phytol. 2007)
Hybridisation• S. pinnatifolius Springbrook tableland variant
(Prentis et al, New Phytol. 2007)
capitulanative seed
invasive seed
S. pinnatifolius (native)
S. madagascariensis (invasive)
Hybrid
Hybridisation multiple outcomes
Introgression Speciation
Extinction
Invasive Native
• 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
Hybridisation
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 selectionExperimental strategy
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’
Genetic mapsLandscape genomics
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
AcknowledgementsAcknowledgementsDrs Peer Schenk (UQ) and Tony Clarke (QUT)Drs Peer Schenk (UQ) and Tony Clarke (QUT)Prof Dave Richardson and Dr John Wilson (Stellenbosch, South Africa)Prof Dave Richardson and Dr John Wilson (Stellenbosch, South Africa)Profs Richard Abbott (St Andrews, UK) and Loren Rieseberg (UBC)Profs Richard Abbott (St Andrews, UK) and Loren Rieseberg (UBC)