Transcript Genetic architecture of adaptation in natural plant populations

The genetics of adaptation in
natural plant populations
Toby Bradshaw &
Doug Schemske
Natural variation = Adaptive variation
• Bad things happen to good genes
• Adaptation must be demonstrated, rather
than assumed
Unanswered questions on adaptive evolution
What is the ‘genetic architecture’ of adaptive
evolution in nature?
• How many genes are involved?
• What is the magnitude of effect of individual mutations?
• Are these mutations dominant, recessive, additive?
What is the identity of genes mutated during
adaptive evolution in nature?
• Structural or regulatory?
• Coding or noncoding?
Are adaptive evolutionary trajectories
predictable and repeatable?
• Does adaptation require specific mutations in a small
subset of key genes?
Genetic architecture of adaptation in natural
plant populations
• Adaptation to bumblebee
or hummingbird
pollinators in Mimulus
• Adaptation to elevation in
Mimulus
• Adaptation to serpentine
soils in Linanthus
Bumblebee-pollinated
Pink
Wide corolla opening
Inserted stigma/anther
1-2ml nectar
Mid-high elevation
Hummingbird-pollinated
Red
Narrow, tubular corolla
Exserted stigma/anther
40-100ml nectar
Low-mid elevation
Components of reproductive isolation in
M. lewisii and M. cardinalis
Pollinator
40.3%
Post-mating
0.9%
Ecology
58.8%
YUP
Mimulus map
Can a single QTL have a large
effect on pollinator choice?
Near-isogenic lines (NILs)
F2
lewisii
NIL1
xL
xL
xL
F1
cardinalis
F2
NIL2
xC
xC
xC
yup
YUP
yup
YUP
N=1090
N=201
Bumblebees
Hummingbirds
yup
YUP
N=180
Bumblebees
yup
YUP
N=3738
Hummingbirds
Visitation rate ratio
BEE:HUMMER
HUMMER:BEE
725
2
15
1284
• A small shift in pollinator assemblage could give YUP mutants an advantage
Visitation rate ratio
BEE
YUP:yup
5.2
5.8
74.1
HUMMER
yup:YUP
1.2
68.0
1.1
• The F2 gave the right answer to the wrong question
• A mutation at the YUP locus increases visitation by the new pollinator ~70-fold,
and this response is symmetrical
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Collect M. lewisii and M. cardinalis from a zone of sympatry
near Mather
Produce 500 F2 lines
Establish all lines in common gardens and allow natural
selection to proceed
Estimate Dp at 200 AFLP loci across the genome
High abs(Dp) is the signature of selection; sign of Dp may
change across elevation if QTL is involved in a tradeoff
Selection at White Wolf (2400m)
# planted
319
319
8146
1-yr survival
55%
27%
44%
1-yr flowering
25%
9%
20%
Dp in progress (Kristy Brady)
Conclusions
• Complex phenotypes, such as reproductive
isolation and fitness, can be measured in nature,
and can be shown to be adaptive.
• The number, chromosome position, magnitude of
effect, and mode of action of QTLs responsible for
adaptation to pollinators can be determined by
genome mapping.
• Substitution of one ‘mutant’ allele at a single locus
controlling flower color can cause immediate
divergence in pollinator preference of a magnitude
much larger than predicted by an F2 population.
• How will we identify the genes responsible for
adaptive variation at QTLs?
FrankenMimulus
Funding
• University of
Washington Royalty
Research Fund
• National Science
Foundation
• Schemske Fund
• Bradshaw Trust