Evolution of Floral Display Sizein a Morning Glory

• Jennifer Lau– Michigan State U.

• Rick Miller– Southeastern

Louisiana U.

• Mark Rausher– Duke University

Ipomoea purpurearoadside in Jalisco, Mexico

note beaker of “stuff” in background

• What is the pattern of selection on floral display size?

• Self-compatible, hermaphroditic plant

• Ipomoea purpurea, common morning glory

• Display size -- number of flowers open on a single day (morning)

Ipomoea purpureaSoybean field in NC, USA

• Pattern of floral presentation varies greatly among plant species

• mass flowering• extended flowering• allocation of limited

resources• why does floral

display size vary?Ipomoea pedicellaris in Oaxaca, Mexico

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5

10

15

20

25

1 2 3 4 5 6 7 8 9 10

Flower number

Nu

mb

er o

f in

div

idu

als

Natural population of Ipomoea purpurea growing in a soybean field in North Carolina

80% flowered1-10 flowers

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Flower number

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Natural population of Ipomoea purpurea growing in a soybean field in North Carolina

22% flowered1-3 flowers

• Experimental results• Array manipulated to

have range of number of flowers

• Selection through male function favors smaller display size

Experimental array ofrandomly arranged genotypes of Ipomoea purpurea

• Experimental results• Array manipulated to

have range of number of flowers

• Selection through male function favors smaller display size

• How did we arrive at this result?

wi/ fi = 1.19 - 0.85 fi

0.7

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1.0

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1.6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Flower number per plant/Proportion of total flowers

Male

fitn

ess

/flow

er

num

ber

2 8 14 20 26 32

Main result

• Dynamics of evolution of floral display size

• Display size and increased selfing through geitonogamy

• Display size and pollen export to other plants

• (Inbreeding depression)

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Male outcrosssuccess

Femaleselfingrate

Display size

Maleselfingsuccess

Totalmalefitness

Inbreedingdepression

Diagram ofdynamics ofevolution offloral display size

Developed byMark Rausher

Total pollenproduced

Pollenremoved

Display size

increasein displaysize

increased visitation

more pollenremoved

+

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Display size

increasedvisitation

increase ingeitonogamouspollen pool

increase inoutcrosspollen pool

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Display size

increase indisplay size

pollinators visitingmore flowers onsame plant withlarger display

great fraction togeitonogamouspollen pool

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Display size

great fraction togeitonogamouspollen pool

unavailable foroutcrossing

smaller fractionto outcross pollen pool

+ -

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Femaleselfingrate

Display size

Maleselfingsuccess

increasedgeitonog.

increasedfemale &male selfingsuccess

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Male outcrosssuccess

Femaleselfingrate

Display size

Maleselfingsuccess

fraction tooutcross pooldecrease withdisplay size

net effect onmale outcrosssuccess positiveor negative

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Male outcrosssuccess

Femaleselfingrate

Display size

Maleselfingsuccess

Totalmalefitness

Inbreedingdepression

Total malefitness issum of:

(1) male selfing success (-id)

(2) male outcrosssuccess

positive or negative

Total pollenproduced

Pollenremoved

Outcrosspollen pool

Geiton.pollen pool

Male outcrosssuccess

Femaleselfingrate

Display size

Maleselfingsuccess

Totalmalefitness

Inbreedingdepression

Empirical study:

Female selfingsuccess

Male outcrosssuccess

Total male fitness

• Array manipulated to have 2, 8, 14, 20, 26, 32 flowers

• 6 inbred lines randomly arranged

• 2 replicates/line32 8 14 26 20 2

8 32 2 26 20 14

Simplified diagram ofexperimental array

• Each array left for one day

• One treatment each day -- 6 days

• Capsules collected• One seed scored for 4

loci• Determine parentage

of each seed• 1224 flowers

monitored (thanks Jen)

• Assume total number of flowers produced by a plant over a season constrained

• Focus on:– Per-flower male selfing success– Per-flower outcross success– Per-flower total male fitness

• Used a likelihood analysis

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0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Flower number per plant/Proportion of total flowers (f)

Selfi

ng r

ate

2 8 14 20 26 32

Female selfing rate increased with number of flowers perplant -- expected with greater geitonogamy

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0.5

1.0

1.5

2.0

2.5

3.0

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Flower number per plant/Proportion of total flowers

Outc

ross

succ

ess

/flow

er

num

ber

2 8 14 20 26 32

Plants with fewer flowers were more successful atfertilizing other plants -- than plants with many flowers

wi/ fi = 1.19 - 0.85 fi

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Flower number per plant/Proportion of total flowers

Male

fitn

ess

/flow

er

num

ber

2 8 14 20 26 32

,11

n

j jjiiii fsxfsw

wi/ fi = 1.19 - 0.85 fi

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Flower number per plant/Proportion of total flowers

Male

fitn

ess

/flow

er

num

ber

2 8 14 20 26 32

On a per-flower basis, significant negative relationshipbetween floral display size and male fitness

wi/ fi = 1.19 - 0.85 fi

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Flower number per plant/Proportion of total flowers

Male

fitn

ess

/flow

er

num

ber

2 8 14 20 26 32

Increased geitonogamous selfing is more than offset by disadvantage of decreased male outcross success

Conclusions

• Increased floral display size is generally accompanied by increased geitonogamous selfing

• Increased visitation and increased geitonogamy have opposite effects on outcross success

• Net effect determines whether selection through male fitness favors large or small displays

Lau, J. A., R. E. Miller, and M. D. Rausher. 2008.Selection through male function favors smaller floral display size in the common morning glory, Ipomoea purpurea (Convolvulaceae). American Naturalist. 172: 63-74.

• William & Joyce Childress• Chris Nacci • Anonymous reviewers• National Science Foundation

Acknowledgements