The genetics of adaptation in natural plant populations

1
The genetics of adaptation in natural plant
populations

• Toby Bradshaw
• Doug Schemske

2
Natural variation Adaptive variation

• Bad things happen to good genes
• Adaptation must be demonstrated, rather than
  assumed

3
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?

4
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

5
Bumblebee-pollinated
Hummingbird-pollinated
Pink
Red
Wide corolla opening
Narrow, tubular corolla
Inserted stigma/anther
Exserted stigma/anther
1-2ml nectar
40-100ml nectar
Mid-high elevation
Low-mid elevation
6
Components of reproductive isolation in M.
lewisii and M. cardinalis
Pollinator 40.3
Post-mating 0.9
Ecology 58.8
7
(No Transcript)
8
Mimulus map
YUP
Can a single QTL have a large effect on
pollinator choice?
9
Near-isogenic lines (NILs)
F2
NIL1
lewisii
xL
xL
xL
F1
cardinalis
F2
NIL2
xC
xC
xC
10
N1090
N201
Bumblebees
Hummingbirds
11
N180
N3738
Bumblebees
Hummingbirds
12
Visitation rate ratio
BEEHUMMER 725 2
HUMMERBEE 15 1284

• A small shift in pollinator assemblage could give
  YUP mutants an advantage

13
Visitation rate ratio
BEE YUPyup 5.2 5.8 74.1
HUMMER yupYUP 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

14
Timberline 3050m
Mather 1400m
Stanford 30m

• 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

15
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)
16
(No Transcript)
17
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?

18
FrankenMimulus
19
Funding

• University of Washington Royalty Research Fund
• National Science Foundation
• Schemske Fund
• Bradshaw Trust