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Risk assessment and Gene flow

Risk assessment and Gene flow. Mike Wilkinson United Kingdom. Contents. Current state of GM technology Principles of risk assessment Defining hazards Measuring exposure Conclusions. Current state of GM technology. Most crops can be genetically modified

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Risk assessment and Gene flow

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  1. Risk assessment and Gene flow Mike Wilkinson United Kingdom

  2. Contents • Current state of GM technology • Principles of risk assessment • Defining hazards • Measuring exposure • Conclusions

  3. Current state of GM technology • Most crops can be genetically modified • Four crops dominate (Maize, Cotton, Soya, oilseed rape) • Herbicide tolerance and insect resistance account for nearly all GM cultivars • Four countries dominate GM production (USA, China, Argentina, Canada)

  4. Future • More GM crops will be commercialised • More countries will approve commercial release • The trend is towards transgene stacking • The next wave of GM crops will target stress tolerance (drought and salt)

  5. Implications for risk assessment As the number of crop-cultivar-gene-gene mixture-location-construct mixes grows, So does the need for generic information to assess risks

  6. Principles of Risk Assessment • RISK • HAZARD • EXPOSURE

  7. Hazard, exposure & risk • Hazard • Adverse effect • Exposure • Frequency/intensity of contact with agent causing adverse effect • Risk • Magnitude and likelihood of an adverse effect A ‘bad thing’ Is it likely the ‘bad thing’ will happen? • a judgement based on ‘how bad’ and ‘how likely’

  8. Risk = f (Hazard, Exposure)

  9. Ecological hazards That a transgene from a GM crop will move into a wild relative AND lead to some form of unwanted ecological change

  10. Crop cross-fertilise Wild species Seed cross-fertilise First generation hybrid Seed Second generation hybrid

  11. Changed abundance/mix of herbivores Invasion of new habitats Changed abundance/mix of predators Replacement of existing genotypes Change pollinator mix in community Out-compete other species in same habitat

  12. Categories of ecological hazard • Relating to the recipient (Direct hazards) • Increased population size within habitat • Invasion of new habitat • Replacement of native genotypes • Relating to other organisms (Indirect hazards) • Decline in sympatric plant species • Changed pollinator abundance • Changed herbivore abundance • Changed predator/parasitoid abundance

  13. Note: The ‘end point’ species may not be the wild recipient

  14. Having defined the hazard What is the exposure?

  15. Exposure pathway concept In chemical toxicology, exposure is to a toxic chemical is simple and direct The ecological hazards represent endpoints in a pathway or matrix of linked events

  16. GM crop F1 hybrid in region Transgene stabilises by introgression Transgene spreads to most populations Enhanced resistance to herbivore depresses herbivore numbers Depressed herbivore numbers cause extinction of specialist parasitoid of the herbivore Wilkinson et al 2003. Trends in Plant Science

  17. GM crop F1 hybrid in region Transgene stabilises by introgression Transgene spreads to most populations

  18. GM crop Generic exposure elements (applies to most transgenes) F1 hybrid in region Transgene stabilises by introgression Transgene spreads to most populations Specific exposure elements (applies to 1-few genes) Hazard

  19. The risk assessment process • Specify and rank the hazards • Quantify generic aspects of exposure • Evaluate aspects of exposure specific to one transgene or GM cultivar • Assess the risks

  20. Stage 1: Specify and rank hazards • Identify cross-compatible recipients • Rank crudely according to likelihood (sympatry, ease of hybridization) • Specify hazards relating to recipient (direct hazards) • Specify hazards relating to sympatric organisms (indirect hazards)

  21. Case Study: Wheat in the USA

  22. 1. Which species are interfertile with wheat?

  23. The tribe Triticeae contains around 330 species in 18 genera and shows ‘an exceptional capacity for intergeneric hybridisation’ Clayton and Renvoize (1986) Breeders define ‘Gene Pool’ groupings of species related to wheat based on taxonomy and ease of crossing

  24. Gene pool 1: Wild species within Triticum ‘Crossing is easy and hybrids fertile’ Triticum monococcum ssp. aegilopoides Triticum urartu Triticum turgidum ssp. dicoccoides Triticum timopheevii ssp. armeniacum ……..Not found in the USA

  25. Gene Pool 2: Closely related Genera ‘All species that will cross with a crop, although with more difficulty than GP1. Hybrids tend to be sterile’ Comprises of species from the following genera: Aegilops (22 species) Amblyopyrum (1 species) Agropyrum (4 species) Dasypyrum (2 species) ……Several species introduced into USA

  26. Gene Pool 3: ‘Wide hybrids’ ‘Gene transfer is not possible without radical techniques’ Includes species from: Agropyrum Elymus (eg couch grass) Hordeum …….Natural hybrids not recorded

  27. Evidence of natural hybrids in Gene Pool 2 ?  At least 12 species Which of these occur in USA?  Aegilops triuncialis Aegilops geniculata Aegilops tauschii Aegilops neglecta Aegilops cylindrica

  28. Wheatproduction in the USA: Harvested area per county for 2000

  29. Species interfertile with wheat found in USA              Aegilops triuncialis  Aegilops geniculata Aegilops tauschii  Aegilops neglecta (positions approximate) Ffffff ff

  30. Distribution of Aegilops cylindrica in USA:1993 USDA survey                        Present Moderate to dense infestations Other records (positions approximate)

  31. Hazards for Aegilops cylindricawhen exposed to GMHT wheat • The transgene (herbicide tolerance) will cause A. cylindrica to become a more aggressive weed (Direct Hazard) • Changed herbicide use on A. cylindrica will cause decline in a named plant or animal species (Indirect Hazards)

  32. Prioritising hazards For any crop-wild relative combination, there are many possible and fewer plausible hazards But comprehensive risk assessment is both expensive and slow So, we need to prioritise hazards

  33. Possible options for ranking hazards • Scarcity of the ‘end point’ species • Cultural importance (Bald Eagle in the USA) • Ecological importance of ‘end point’ species • Agronomic or medicinal value of ‘end point’ species • Cuddliness of ‘end point’ species

  34. Stage 2: quantify exposure Generic exposure elements Specific exposure elements

  35. Quantify generic elements of exposure • Quantify hybridization • Quantify introgression • Quantify gene spread

  36. Quantifying hybrid formation Important to define • Context of contact (weed or adjacent wild population) • Distribution of crop and recipient species • Relationship between hybrid frequency and separation, donor/recipient population size • Crop rotation patterns

  37. 1. Context of contact Cultivated and wild Helianthus annuus, Nebraska USA, in sympatry

  38. 2. Crop and recipient distribution

  39. Sunflowerproduction in the USA: Harvested area per county for 2000 ??

  40. Wild Helianthus annus in the USA (data incomplete) – USDA NRCS 2001  wild Helianthus annuus

  41. This scale is too crude So use • Direct surveys • Literature • Remote sensing • Herbarium specimens

  42. 3. Importance of separation and population size on hybrid frequency • Direct measures of gene flow • Seed collections • Hybrid plant screens • Modelled gene flow • Pollen dispersal models • Seed dispersal models

  43. Direct measures • Sampling strategy • Representative sample of the field/population • Need for markers to handle large numbers • Transgene • Physiological/ phenotypic screen • Flow cytometry • Confirmation of hybrid status • Molecular analysis (microsatellites/ locus-specifc PCR)

  44. Modelling gene flow • Need pollen dispersal curves • Population sizes • Life history details

  45. 4. Crop rotation patterns • Farmer’s records • Remote sensing

  46. Crop rotation in the target area/nation

  47. 2. Quantify Introgression Locus transmission rates in the field will be influenced by drag imposed by crop genes • Gametic disequilibrium • Linkage disequilibrium Possibly countered by fitness advantage of transgene

  48. Measuring introgression • Map historic introgression of mapped neutral markers to establish position effects • Note introgression profiles of mapped markers in glasshouse conditions to study effects of chromosome pairing

  49. 3. Transgene spread • Detailed distribution of recipient • Proportion of populations exposed to gene flow • Gene exchange rates between populations • Demography of recipient

  50. Combine to hybridization introgression and gene spread data to quantify generic elements of exposure

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