Evolution of Floral Display Size in a Morning Glory

1. Evolution of Floral Display Sizein 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

2. 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

3. 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

4. 80% flowered 1-10 flowers Natural population of Ipomoea purpurea growing in a soybean field in North Carolina

5. 22% flowered 1-3 flowers Natural population of Ipomoea purpurea growing in a soybean field in North Carolina

6. 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

7. Main result • 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?

8. Dynamics of evolution of floral display size • Display size and increased selfing through geitonogamy • Display size and pollen export to other plants • (Inbreeding depression)

9. Developed by Mark Rausher Display size Total pollen produced Pollen removed Outcross pollen pool Male outcross success Geiton. pollen pool Diagram of dynamics of evolution of floral display size Total male fitness Female selfing rate Male selfing success Inbreeding depression

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

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

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

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

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

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

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

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

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

19. 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)

20. 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

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

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

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

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

26. 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

27. 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