Evolution of Floral Display Size in a Morning Glory Jennifer Lau –Michigan State U. Rick Miller –Southeastern Louisiana U. Mark Rausher –Duke University Ipomoea purpurea roadside 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 purpurea Soybean 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

Natural population of Ipomoea purpurea growing in a soybean field in North Carolina 80% flowered 1-10 flowers

Natural population of Ipomoea purpurea growing in a soybean field in North Carolina 22% flowered 1-3 flowers

Experimental results Array manipulated to have range of number of flowers Selection through male function favors smaller display size Experimental array of randomly 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? 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 pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Male outcross success Female selfing rate Display size Male selfing success Total male fitness Inbreeding depression Diagram of dynamics of evolution of floral display size Developed by Mark Rausher

Total pollen produced Pollen removed Display size increase in display size increased visitation more pollen removed +

Total pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Display size increased visitation increase in geitonogamous pollen pool increase in outcross pollen pool

Total pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Display size increase in display size pollinators visiting more flowers on same plant with larger display great fraction to geitonogamous pollen pool

Total pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Display size great fraction to geitonogamous pollen pool unavailable for outcrossing smaller fraction to outcross pollen pool + -

Total pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Female selfing rate Display size Male selfing success increased geitonog. increased female & male selfing success

Total pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Male outcross success Female selfing rate Display size Male selfing success fraction to outcross pool decrease with display size net effect on male outcross success positive or negative

Total pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Male outcross success Female selfing rate Display size Male selfing success Total male fitness Inbreeding depression Total male fitness is sum of: (1) male selfing success (-id) (2) male outcross success positive or negative

Total pollen produced Pollen removed Outcross pollen pool Geiton. pollen pool Male outcross success Female selfing rate Display size Male selfing success Total male fitness Inbreeding depression Empirical study: Female selfing success Male outcross success Total male fitness

Array manipulated to have 2, 8, 14, 20, 26, 32 flowers 6 inbred lines randomly arranged 2 replicates/line Simplified diagram of experimental 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

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

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

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

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 Selection through male function favors smaller floral display size in the common morning glory, Ipomoea purpurea (Convolvulaceae). American Naturalist. 172: William & Joyce Childress Chris Nacci Anonymous reviewers National Science Foundation Acknowledgements