What makes a species invasive? f) Micro-evolutionary change hypothesis

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

2. What makes a species invasive? • f) 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. What makes a species invasive? • f) 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 • Climate matching = different genetic stock succeed in different parts of introduced range; often correspond to similar latitudes or climate in native range. e.g. tamarisk in US.

4. What makes a species invasive? • f) 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

5. What makes a species invasive? • f) 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

6. What makes a species invasive? • f) 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

7. What makes a species invasive? • f) 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

8. What makes a species invasive? • f) 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 • e.g.. Bearded Goatgrass in CA: ‘competitive’ VS ‘seed producing’ phenotypes in invasion front VS monoculture.

9. What makes a species invasive? • f) 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 vs. reproductive pressures e.g. Leger 2003.

10. What makes a species invasive? • f) 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

11. What makes a species invasive? • f) 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

12. What makes a species invasive? • f) 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

13. What makes a species invasive? • f) 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

14. What makes a species invasive? • f) 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

15. What makes a species invasive? • f) 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

16. What makes a species invasive? • f) 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

17. Determining genetic change and hybridization • How?

18. Determining genetic change and hybridization • How? • Morphology and cytology • Genetic analyses – chloroplast, nuclear, ribosomal DNA • Experiments (common garden)

19. What makes a species invasive? • f) Micro-evolutionary change hypothesis • Hybridization Evidence: • Stabilized introgressants • Introgression = back cross with 1 or more parents • P1 X P2 → F1 • F1 X {P1, P2} → F2 introgressant

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

21. What makes a species invasive? • f) Micro-evolutionary change hypothesis • Hybridization Evidence: • Stabilized introgressants • Hybrids form new Intraspecific taxa

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

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

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

25. What makes a species invasive? • f) Micro-evolutionary change hypothesis • Specific Example: 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

26. What makes a species invasive? • f) Micro-evolutionary change hypothesis • Specific Example: 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

27. What makes a species invasive? • f) Micro-evolutionary change hypothesis • Specific Example: 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

28. What makes a species invasive? • f) Micro-evolutionary change hypothesis • Specific Example: 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

29. Another example: Tamarisk in US • Gaskin and Shaal 2002. PNAS 99 (17): 11256-11259 • Used DNA sequencing to determine origins and relationships of plants (nuclear gene intron) • Little similarity in genetic types between US and Eurasia (4 common of 58 types) • Most common species in US invasion was hybrid between 2 Eurasian species (Tamarix chinensis and Tamarix ramosissima) • Hybrid unknown in Asia (species geographically isolated)

30. Evidence for genetic change in invasive species • Leger and Rice 2003, Eschultzia californica • Used common garden to look for genetic VS phenotypic traits • Plants from Chile (invaded range) were larger with no competitors

31. Leger and Rice 2003. Ecology Letters

33. What makes a species invasive? • f) 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

34. What makes a species invasive? • f) 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

35. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies

36. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies • Alien species are immigrants to a new area • Aliens often arrive as seeds

37. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies • Alien species are immigrants to a new area • Aliens often arrive as seeds • In other words, they arrive without the grazers, insect pests, diseases, parasites, etc. of their native range – their “enemies”

38. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies • Alien species immigrate without enemies • Hence, alien species “escapes” from their enemies and are no longer affected by biotic constraints • Thus, alien growth and success is much greater in new range

39. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies • Alien species immigrate without enemies • Aliens lack biotic constraints • However, alien success will depend on potential enemies in new range: • Are potential enemies generalists or specialists?

40. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies • Alien species immigrate without enemies • Aliens lack biotic constraints • However, alien success will depend on potential enemies in new range: • Are potential enemies generalists or specialists? • Are population sizes of potential enemies large or small?

41. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies • Alien species immigrate without enemies • Aliens lack biotic constraints • However, alien success will depend on potential enemies in new range: • Are potential enemies generalists or specialists? • Are population sizes of potential enemies large or small? • Do potential enemies feed on foliage or seeds?

42. What makes a species invasive? • g) Escape from biotic constraints hypothesis • aka “Escape from enemy” hypothesis • “Enemy release” hypothesis • Basic concepts: • Species in their native range are suppressed by natural enemies • Alien species immigrate without enemies • Aliens lack biotic constraints • However, alien success will depend on potential enemies in new range: • Are potential enemies generalists or specialists? • Are population sizes of potential enemies large or small? • Do potential enemies feed on foliage or seeds? • Are there similar hosts for potential enemies in new area?