Post on 21-Dec-2015
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
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) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecks = loss of genetic variation when population
size drastically decreases; often associated with catastrophic events that result in mass mortality
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift = loss of genetic variation by chance when
populations are small and do not have complete, random interbreeding
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selection: strong selective forces often apply to successful colonizers
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environment – rapid adaptive responses over short
times and within short distances to new environment
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment – shifts in relative proportions of
competition vs. defense pressures
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment
• Hybridization – a natural process that occurs in plants
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment
• Hybridization – a natural process that occurs in plants↑ genetic diversity
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment
• Hybridization – a natural process that occurs in plants↑ genetic diversity↓reproductive barriers
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment
• Hybridization – a natural process that occurs in plants↑ genetic diversity↓reproductive barriersTransfers or originates adaptations
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment
• Hybridization – a natural process that occurs in plants
2834 plant species in the British IslesOf these, 715 (25%) are hybrids
74 are native X alien21 are alien X alien95 (13% of hybrids) involve aliens
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment
• HybridizationInterspecific – often with other species in new environment
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Micro-evolutionary change hypothesis• Frequent colonizing events
Founder effectsGenetic bottlenecksGenetic drift
• Natural selectionNew abiotic environmentNew biotic environment
• HybridizationInterspecificIntraspecific – often with populations from native range that would
not normally occur
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Hybridization Evidence:• Stabilized introgressants
Introgression = back cross with 1 or more parentsP1 X P2 → F1
F1 X {P1, P2} → F2 introgressant
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Hybridization Evidence:• Stabilized introgressants
Introgression = back cross with 1 or more parentsStabilized = viable, fertile hybrids
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Hybridization Evidence:• Stabilized introgressants
Hybrids form new Intraspecific taxa
3) What makes a species invasive?c) Micro-evolutionary change hypothesis
Hybridization Evidence:• Stabilized introgressants
Hybrids form new intraspecific taxaHybrids form new Species – Note: all examples are alien X alien
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
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
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
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
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 SpainBut subsequent introductions likely, especially from Black Sea
areaAlso can’t tell from morphological information where it came from,
but know from morphology that had to hybridize at some timeR. ponticum cultivated along with other introduced species
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
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
speciesOccurrence of R. catawbiense genotypes most common in
Scotland (coldest area of British Isle)Introgression with catawbiense appears to have conferred cold
tolerance into ponticum
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 control2 species particularly invasive:Tamarix ramosissima & T. chinensis
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 homozygousT. ramosissima: Haplotype 1 (blue) most abundant, but also
others; fewer homozygotes, many heterozygotes• No T. ramosissima -T. chinensis hybrids (red-blue combinations)
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
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
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 selectionIn other words micro-evolutionary changes
• Good evidence for hybridization being beneficial
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