1. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events are a central feature of invasive plants

2. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects = founders of a new population carry only a fraction of the total genetic variation of the source populations

3. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks = loss of genetic variation when population size drastically decreases; often associated with catastrophic events that result in mass mortality

4. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift = loss of genetic variation by chance when populations are small and do not have complete, random interbreeding

5. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection: strong selective forces often apply to successful colonizers

6. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment – rapid adaptive responses over short times and within short distances to new environment

7. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment – shifts in relative proportions of competition vs. defense pressures

8. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants

9. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants ↑ genetic diversity

10. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants ↑ genetic diversity ↓reproductive barriers

11. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants ↑ genetic diversity ↓reproductive barriers Transfers or originates adaptations

12. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization – a natural process that occurs in plants 2834 plant species in the British Isles Of these, 715 (25%) are hybrids 74 are native X alien 21 are alien X alien 95 (13% of hybrids) involve aliens

13. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization Interspecific – often with other species in new environment

14. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Micro-evolutionary change hypothesis Frequent colonizing events Founder effects Genetic bottlenecks Genetic drift Natural selection New abiotic environment New biotic environment Hybridization Interspecific Intraspecific – often with populations from native range that would not normally occur

15. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Introgression = back cross with 1 or more parents P 1 X P 2 → F 1 F 1 X {P 1, P 2 } → F 2 introgressant

16. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Introgression = back cross with 1 or more parents Stabilized = viable, fertile hybrids

17. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Hybrids form new Intraspecific taxa

18. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Hybrids form new intraspecific taxa Hybrids form new Species – Note: all examples are alien X alien

19. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Allopolyploids = hybrid between different species in which chromosomes of both parents are retained

20. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Hybridization Evidence: Stabilized introgressants Allopolyploids Hybrids form new Species – Note: both Tragopogon’s are alien X alien

21. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9:541-556 Natural distribution: south of Black Sea with disjunct populations in Lebanon, Spain, & Portugal

22. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9:541-556 Natural distribution: south of Black Sea with disjunct populations in Lebanon, Spain, & Portugal Extensively naturalized throughout British Isles

23. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9:541-556 Natural distribution: south of Black Sea with disjunct populations in Lebanon, Spain, & Portugal Extensively naturalized throughout British Isles Origin unclear: Earliest known introduction (1763) from Spain But subsequent introductions likely, especially from Black Sea area Also can’t tell from morphological information where it came from, but know from morphology that had to hybridize at some time R. ponticum cultivated along with other introduced species

24. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9:541-556 Most individuals from naturalized populations had genotypes from Spain (88%), followed by Portugal (10%) No genotypes from Black Sea region

25. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Rhododendron ponticum in British Isles *Milne & Abbott (2000) Molecular Ecology 9:541-556 Most individuals from naturalized populations had genotypes from Spain (88%), followed by Portugal (10%) No genotypes from Black Sea region Small number of individuals had hybridized with at least 3 other species Occurrence of R. catawbiense genotypes most common in Scotland (coldest area of British Isle) Introgression with catawbiense appears to have conferred cold tolerance into ponticum

26. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Tamarix in US *Gaskin & Schaal (2002) PNAS 99:11256-11259 Native range: 54 species across Europe & Asia Introduced range: originally 8-12 species into US for shade & for erosion control 2 species particularly invasive: Tamarix ramosissima & T. chinensis

27. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Tamarix in US *Gaskin & Schaal (2002) PNAS 99:11256-11259 In native ranges: T. ramosissima & T. chinensis overlap But different genotypes from DNA sequencing T. chinensis: Haplotype 2 (red); primarily homozygous T. ramosissima: Haplotype 1 (blue) most abundant, but also others; fewer homozygotes, many heterozygotes No T. ramosissima -T. chinensis hybrids (red-blue combinations)

28. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Tamarix in US *Gaskin & Schaal (2002) PNAS 99:11256-11259 In US: ~20% genotypes are T. ramosissima homozygotes (blue-blue) ~20% genotypes are T. chinensis homozygotes (red-red) ~20% genotypes are T. ramosissima -T. chinensis hybrids (red- blue) Also get novel genotypes plus hybrids with other Tamarix species

29. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis Case Study: Tamarix in US *Gaskin & Schaal (2002) PNAS 99:11256-11259 In US: ~20% genotypes are T. ramosissima homozygotes (blue-blue) ~20% genotypes are T. chinensis homozygotes (red-red) ~20% genotypes are T. ramosissima -T. chinensis hybrids (red- blue) Also get novel genotypes plus hybrids with other Tamarix species Complicates biological control efforts in US

30. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis SUMMARY: Micro-evolutionary change hypothesis Likely that most (if not all) invasive species go through founder events, experience genetic bottlenecks & drift, and undergo selection In other words micro-evolutionary changes Good evidence for hybridization being beneficial

31. 3)What makes a species invasive? c) Micro-evolutionary change hypothesis SUMMARY: Micro-evolutionary change hypothesis Likely that most (if not all) invasive species go through micro- evolutionary changes Good evidence for hybridization being beneficial But Have evidence of micro-evolutionary changes for only a limited number of species For only a subset of these, have evidence that micro-evolutionary changes have been beneficial A species that undergoes micro- (or even macro-) evolutionary changes does not automatically become invasive