Pollinator-mediated floral evolution and speciation in southern African Iridaceae

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Part 3 of the 2010 ACEBB seminar series, Dr Paul Rymer presents "Pollinator-mediated floral evolution and speciation in southern African Iridaceae."

Abstract: Explaining the rapid diversification of flowering plants remains one of the greatest challenges facing evolutionary biologists. The pollinator-shift hypothesis developed by Grant (1949) and Stebbins (1970) is the most widely accepted explanation. However, pollinator mediated selection is yet to be shown to result in speciation. The focus of my investigation has been biodiversity hotspots in southern Africa, primarily because they harbour exceptional plant species diversity and endemism, and therefore the promise of detecting speciation in action. In an attempt to unravel the processes driving the evolution of floral traits and speciation, I have taken a multi-faceted approach. I will present my findings from three very different studies:

1. Macroevolution in Sparaxis (Iridaceae),
2. Population genetics in Gladiolus carinatus species complex (Iridaceae),
3. Mating patterns in Gladiolus longicollis (Iridaceae). These studies highlight the role of pollination in recent and continuous speciation events.

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Pollinator-mediated floral evolution and speciation in southern African Iridaceae

  1. 1. The Environment Institute The Australian Centre for Evolutionary Biology and Biodiversity ACEBB Seminar Series Pollinator-mediated floral evolution and speciation in southern African Iridaceae Dr Paul Rymer
  2. 2. Pollinator-mediated floral evolution and speciation in southern African Iridaceae Paul D. Rymer 1,2, Vincent Savolainen 1,2 John C. Manning 3, Peter Goldblatt 4, Steven D. Johnson 5 1 Imperial College London, Silwood Park, UK 2 Royal Botanic Gardens Kew, Jodrell Laboratory, UK 3 South African National Biodiversity Institute, Kirstenbosch, S. Africa 4 Missouri Botanical Garden, St. Louis, U.S.A. 5 University of Kwa-Zulu-Natal, Botany and Zoology, S. Africa EUROPEAN COMMISSION Marie Curie Actions - IIF
  3. 3. Talk outline • Diversification of flowering plants – biodiversity hotspots in southern Africa • Macroevolution – Sparaxis (Iridaceae) • Population genetics – Gladiolus carinatus species complex (Iridaceae) • Mating patterns – Gladiolus longicollis (Iridaceae) • Current and future research – Another ‘Great Southern Land’
  4. 4. Diversification of flowering plants • The “abominable mystery” Charles Darwin Associated with a shift from wind to animal mediated pollination
  5. 5. Evolution of floral traits Whittall & Hodges (2007) Nature, 447: 706-10
  6. 6. Biodiversity hotspots • Southern Africa – Cape Floristic Region – Succulent Karoo Vitals CFR SK Hotspot Original Extent (km 2) 78.555 102,691 Hotspot Vegetation Remaining (km 2) 15.711 29,780 Endemic Plant Species 6.210 2,439 Area Protected (km 2) 10.859 2,567 Area Protected (km 2) in Categories I-IV* 10.154 1,890 http://www.biodiversityhotspots.org/
  7. 7. Macroevolution • Evolution of traits across a phylogeny – Avoid bias and false trends (Felsenstein 1985) Without controlling for phylogeny, one or a few species-rich clades with a trait could strongly bias our interpretations and create an apparent trend where none actually exists
  8. 8. Sparaxis (Iridaceae)
  9. 9. Phylogenetic analysis • Taxonomic relationships – Monophyly of Sparaxis – Species delimitation • Evolution of traits – Floral traits and pollination syndromes Sampling (54 taxa) Sequencing • Outgroups (15) – Plastid loci (3106 bp) • 100% species (16) +  trnV, trnQ, rpl32 subspecies (6) – Nuclear loci (569 bp) • Multiple accessions  RPB2 (1-4/taxa)
  10. 10. Sparaxis molecular phylogeny Sparaxis is a monophyletic genus, sister to Duthiastrum RAxML tree based on plastid and nuclear loci
  11. 11. Sparaxis molecular phylogeny • 2 major clades • 5 subclades • Most species relationships remain unresolved RAxML tree based on plastid and nuclear loci
  12. 12. Pollination syndromes
  13. 13. Ancestral trait reconstruction Ancestral state = Bee pollination Independent transitions – bee (to generalist) to beetle – bee to long proboscid fly
  14. 14. Evolutionary trait shifts Tube elongation Tube elongation Long proboscis fly Long proboscis fly Bee Symmetry Colour Bee + beetle Beetle
  15. 15. Macroevolution Summary • Developed a partially resolved molecular phylogeny for the genus Sparaxis – Confirm monophyly and sister-species • Reconstructed ancestral characters – Two major transitions from bee to fly or beetle
  16. 16. Population genetics • Fills the gap between phylogenetics and experimental ecology • Coalescent analysis – Estimate divergence times, historical gene flow & ancestral population sizes • Genome scans – Detect genetic signatures of selection – Identify candidate loci
  17. 17. Gladiolus carinatus species complex GcB GcY G. carinatus (blue and yellow morph) Gg Gq G. griseus G. quadrangulus
  18. 18. GcB GcY Gg Gq GcB 1 0.33* 0.86 0.86 GcY 1 0.00 0.67 Gg 1 0.29 Gq 1
  19. 19. Floral differentiation Species differentiation – Gq isolated – Gg and Gc partial overlap
  20. 20. Coalescent analysis “Isolation-with-Migration” model (Hey & Nielsen 2004)
  21. 21. Genome scans Genetic signatures of selection can be elucidated from large genomic datasets, where genes with... increased population differentiation... may be candidates for selected loci (Nielsen 2005)
  22. 22. Genome scans - species
  23. 23. Genome scans - morphs
  24. 24. Speciation candidate loci Genetic divergence (Fst) Association with floral traits Fragment Global Gq / Gq / Gg / Gg / Gg / GcB / timing number size shape colour size-label analysis Gg Gc Gc GcB GcY GcY 106-B species * 0.875 0.823 † -0.050 0.011 0.040 NS NS ** ** ** 134-G species * 0.580 0.884 † 0.168 0.148 0.241 0.016 ** NS ** ** ** † species, 91-G , 0.394 0.867 ‡ 0.308 † 0.314 ‡ 0.200 -0.002 NS NS ** ** ** morphs ‡ 324-B morphs * -0.014 0.561 0.390 † 0.362 † 0.508 † 0.051 NS NS ** ** NS 186-G morphs * -0.030 0.273 0.318 † 0.292 ‡ 0.318 ‡ -0.017 NS NS <0.001 <0.001 NS 169-B morphs ‡ 0.487 0.044 0.352 † 0.332 ‡ 0.247 -0.017 <0.001 <0.001 NS NS NS 89-B morphs ‡ 0.149 0.009 § 0.256 ‡ 0.347 † 0.200 0.017 NS NS NS NS NS 225.5-G morphs ‡ 0.329 0.034 0.232 ‡ 0.328 † 0.115 0.079 ** ** NS NS NS 187-G morphs † 0.077 0.172 0.416 * 0.332 ‡ 0.374 -0.021 NS NS <0.001 NS NS 154-B morphs † -0.037 § 0.316 0.348 † 0.314 ‡ 0.332 -0.024 NS NS ** <0.001 NS 291-B morphs ‡ 0.281 -0.004 § 0.219 -0.011 0.508 † 0.393 * NS NS NS NS **
  25. 25. Neutral and selected loci Population structure, but no differentiation of Gc-Gg
  26. 26. Neutral and selected loci All species form distinct clusters
  27. 27. Population genetics Summary • Evidence for recent and continuous speciation in the face of gene flow • Facilitated by a few loci associated with shifts in floral traits
  28. 28. Mating patterns • Gene flow needs to be halted for speciation to proceed to completion • Assortative mating – Sympatric / secondary contact • Floral traits may be ‘magic traits’
  29. 29. Gladiolus longicollis (Iridaceae) Corolla tube 8 – 12 cm Hawkmoth syndrome • white • tubular flowers • open at night Corolla tube 3 – 6 cm • scented
  30. 30. Hawkmoth pollinators
  31. 31. Pollinator behaviour Long morph Nectar Pollen Visits Seed 10.1 ± high high high 1.9 mm 0.6 ± high density high 0.4 mm Short morph Nectar Pollen Visits Seed 2.7 ± none density none 0.5 mm 2.7 ± high high high 0.5 mm
  32. 32. Predictions • Intermediate morphs will have reduced reproductive success • Most pollination events will be within morphs • Between morph pollination events will be infrequent and vary in reproductive success – Density dependent
  33. 33. Distribution pattern
  34. 34. Study population
  35. 35. Population census • 2 flowering seasons • 4 day/night census • Map & tag plants • Measure traits – Corolla tube length – Dorsal tepal length – Height of flower – Leaf length – Colour (subsample) – Shape (subsample) – Scent (subsample) • Reproductive success – Capsule maturation – Seed production
  36. 36. Genetic analysis • Developed SSR markers – 5 loci (Combined non-exclusion probability 0.00119) Locus N # alleles Ho He GL17 859 16 0.733 0.781 GL35 836 57 0.847 0.956 GL41 855 19 0.735 0.904 GL63 871 40 0.885 0.948 GL65 846 41 0.856 0.955 • Extracted DNA – 128 (2007) and 321 (2008) flowering plants – 30 (2007) and 32 (2008) progeny arrays • 600 germinated seed (95-100%)
  37. 37. Mating patterns MLTR (Ritland 1991) 2007 2008 Multilocus outcrossing = tm (SD) 0.979 (0.074) 0.992 (0.100) Singlelocus outcrossing = ts (SD) 0.851 (0.025) 0.876 (0.031) Biparental inbreeding = tm-ts (SD) 0.128 (0.068) 0.116 (0.086) Correlation of outcrossing (SD) 0.129 (0.502) 0.923 (0.539) 1/(number of sires) = rp (SD) 0.290 (0.067) 0.383 (0.065) High levels of outcrossing with some biparental inbreeding Large variation in outcrossing rates in 2007
  38. 38. Dispersal curves Frequent short dispersal with fat tale (max 3.94km)
  39. 39. Correlation of tube length • 2007 (low density) assortative mating • 2008 (high density) significant mating among morphs
  40. 40. Mating patterns Summary • Assortative mating among morphs • Between morph pollination events are NOT infrequent... especially at high densities
  41. 41. Current and future research • Population genetic – Hybrid determination – Differential selection • Reinforcement of traits – Common garden experiment • Coevolution of hawkmoth pollination – Geographic mosaic
  42. 42. Current and future research • Comparative analysis of hotspot evolution – Western Cape – Southwest Australia • Convergent evolution of floral traits • Role of standing genetic variation • Adaptation to climate change
  43. 43. Acknowledgements Kew NHM • Mark Chase • Ian Kitching • Felix Forest • Jan Schnitzler Gladiolus longicollis • Kit Strange • Steve Johnson • Sandy-Lynn Steenhuisen Silwood • Ruth Cozien • Vincent Savolainen • Bruce Anderson • Martyn Powell • Ronny Alexandersson • Joaquin Hortal • Celine Devaux Sparaxis • Cuong Tang • John Manning • Peter Goldblatt • Clare Dean
  44. 44. General questions + comments
  45. 45. Pollination Ecoregion Bee S. Karoo Generalist Lowland HBSPF Highland LPF
  46. 46. Reinforcement of traits - coarse grained • Compare virgin and 2nd contact areas – Reproductive ecology – Population genetics – Common garden
  47. 47. Quantitative genetics • Common garden of material collected from virgin areas and secondary contact areas – Detect shifts + heritability of floral traits
  48. 48. Scent analysis (a) Linalool (b) Methyl benzoate (c) Benzaldehyde 100 50 70 t = 16.06 t = 2.35 t = 0.74 P < 0.001 60 P = 0.47 80 40 P = 0.02 50 60 40 30 40 30 20 20 20 10 10 1.5 0 0 Short-tubed morph 0 Long-tubed morph Percentage of total ion count Short Long Short Long Short Long 1.0 (d) Ocimene (e) Phenylacetaldehyde (f) Benzyl acetate 80 35 40 t = 6.43 t = 3.71 t = 5.12 0.5 P < 0.001 30 P = 0.002 P < 0.001 30 Dimension 2 60 25 20 20 0.0 40 15 20 10 10 5 -0.5 0 0 0 Short Long Short Long -1.0 Short Long (g) Eugenol (h) Benzyl alcohol (i) Phenylethyl acetate -1.5 1.6 1.0 0.35 t = 1.53 t = 4.96 t = 4.89 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 1.4 0.30 P = 0.14 0.8 P < 0.001 P < 0.001 1.2 0.25 Dimension 1 1.0 0.6 0.20 0.8 0.4 0.15 0.6 0.10 0.4 0.2 0.2 0.05 0.0 0.00 0.0 Short Long Short Long Short Long
  49. 49. Bimodal pattern floral tube and moth tongue length Anderson et al submitted to Evolution
  50. 50. Selection against intermediates Cross pollination by hand Pollen limitation? Natural pollination Anderson et al submitted to Evolution
  51. 51. Is there any incompatibility among morphs? Pollen parent Int Short Long Int Short Long Int Short Long 160 140 No significant reduction in seed set among crosses, Intermediates can have high seed set 120 except long mothers crossed with short fathers Mean seed set AB AB 100 BCD B BC AB AB 80 4 AD 26 60 AC 17 7 2 20 40 16 20 5 2 0 Int Int Int Short Short Short Long Long Long Anderson et al submitted to Evolution Ovule parent
  52. 52. The Environment Institute The Australian Centre for Evolutionary Biology and Biodiversity Next seminar Environmental Genomics Dr Chris Hardy

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