Transcript Andy_Lowe
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) Hybrid capitula native seed Undue influence by fireweed on level of hybridisation in native -asymmetric hybridisation invasive seed Hybridisation • S. pinnatifolius Springbrook tableland variant (Prentis et al, New Phytol. 2007) S. pinnatifolius (native) S. madagascariensis (invasive) Hybrid capitula native seed No viable hybrids found at field site, hybrids are not developing and are therefore gamete sink 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 S. pinnatifolius S. madagascariensis Total seed (plant) 505 422 Post germination 338 304 Post establishment 274 252 Hybridisation (20% fireweed) 225 245 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)