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)