Pollinator-mediated Speciation in Angiosperms: What Do We Know?

Lecture Overview Vascular plant diversity Modes of angiosperm speciation Pollination modes and angiosperm diversification Experiments: pollinator-mediated selection on floral traits Conclusions

Lecture Overview Vascular plant diversity Modes of angiosperm speciation Pollination modes and angiosperm diversification Experiments: pollinator-mediated selection on floral traits Conclusions

Vascular Plant Diversity 260,000+ species

Vascular Plant Diversity 260,000+ species ~ 850 gymnosperms (290 mya) ~ 9800 ferns and fern allies (400 mya) ~ 249,000 angiosperms (130 mya)

Rapid diversification of angiosperms: “Abominable mystery”

His attempt to identify a single cause: “wretchedly poor”

Lecture Overview Vascular plant diversity Modes of angiosperm speciation Pollination modes and angiosperm diversification Experiments: pollinator-mediated selection on floral traits Conclusions

Modes of Angiosperm Speciation (speciation = reproductive isolation)

Mechanical barriers (e.g., mountain range)

Modes of Angiosperm Speciation (speciation = reproductive isolation) Mechanical barriers (e.g., mountain range) Genomic events - polyploidy (e.g., diploid to tetraploid)

Modes of Angiosperm Speciation (speciation = reproductive isolation) Mechanical barriers (e.g., mountain range) Genomic events - polyploidy (e.g., diploid to tetraploid) - chromosomal rearrangements

Modes of Angiosperm Speciation (speciation = reproductive isolation) Mechanical barriers (e.g., mountain range) Genomic events - polyploidy (e.g., diploid to tetraploid) - chromosomal rearrangements - Pollinator-mediated reproductive isolation - evolution of different floral morphologies

Lecture Overview Vascular plant diversity Modes of angiosperm speciation Pollination modes and angiosperm diversification Experiments: pollinator-mediated selection on floral traits Conclusions

Pollination Mode and Diversification Pollination = transfer of pollen to stigma

Anther Stigma Petal Sepal

Anther Stigma Petal Sepal

Anther Stigma Petal Sepal

Pollination Mode and Diversification Pollination = transfer of pollen to stigma - > 99% of gymnosperm species wind-pollinated

Pollination Mode and Diversification Pollination = transfer of pollen to stigma - > 99% of gymnosperm species wind-pollinated - > 80% of angiosperms are animal-pollinated

Pollinators and angiosperm speciation: correlations Angiosperm and insect diversification co- occurred

Pollinators and angiosperm speciation: correlations Angiosperm and insect diversification co- occurred Animal-pollination correlated with species richness at family level

Correlation ≠ Causation

Blood Pressure Income

Lecture Overview Vascular plant diversity Modes of angiosperm speciation Pollination modes and angiosperm diversification Experiments: pollinator-mediated selection on floral traits Conclusions

Two Important Studies Polemonium viscosum (alpine skypilot) and bumblebees (Galen, 1996)

Timberline 11,000 ft. Corolla tube width = 16 mm

Timberline 11,000 ft. Alpine - 12,000 ft. Corolla tube width = 18 mm Corolla tube width = 16 mm

Timberline 11,000 ft. Alpine - 12,000 ft. Corolla tube width = 18 mm Corolla tube width = 16 mm = 11% difference in corolla tube width

Timberline 11,000 ft. Alpine - 12,000 ft. Corolla tube width = 18 mm Corolla tube width = 16 mm What explains corolla tube width difference? = 11% difference in corolla tube width

Timberline 11,000 ft. Alpine - 12,000 ft. Corolla tube width = 18 mm Corolla tube width = 16 mm What explains corolla tube width difference? Solitary bees

Timberline 11,000 ft. Alpine - 12,000 ft. Corolla tube width = 18 mm Corolla tube width = 16 mm What explains corolla tube width difference? Solitary bees Bumble bees

Conclusions Bumblebees selected for wide corolla Evolution from 16mm to 18 mm corolla ~20 yrs Pollinator preference can cause floral trait evolution

Two Important Studies Polemonium viscosum (alpine skypilot) and bumblebees (Galen, 1996) Ipomopsis aggregata (scarlet gilia) and hummingbirds (Campbell et al., 1997)

Experiment Results Mean corolla tube width Visits/ flower/ hr.

Experiment Results Mean corolla tube width Visits/ flower/ hr. Wider Flowers = More Pollen Export

Experiment Results Mean corolla tube width Visits/ flower/ hr. Optical Density More redLess red Wider Flowers = More Pollen Export Seed set/ flower

Experiment Results Mean corolla tube width Visits/ flower/ hr. Optical Density More redLess red Wider Flowers = More Pollen Export Seed set/ flower Redder Flowers = More Seed

Conclusions Floral traits can determine level of pollinator attraction Pollinator preference caused plant reproductive success differences

Reproductive isolation in columbine Aquilegia pubescens Aquilegia formosa

Reproductive isolation in columbine Aquilegia pubescens Aquilegia formosa Note - viable hybrids from hand pollination

Aquilegia pubescens Aquilegia formosa

Aquilegia pubescens Aquilegia formosa

Experimental Design (Fulton and Hodges, 1999)

Results Hummingbirds almost always visit A. formosa

Results Hummingbirds almost always visit A. formosa Hawkmoths always visit A. pubescens

Conclusion Pollinator preference based on corolla morphology resulted in reproductive isolation

Any problems with this study?

No hybrids in array - not a complete test of pollinator preference

Any problems with this study? No hybrids in array - not a complete test of pollinator preference Need to show that hybrids attract mix of pollinator types

Any problems with this study? No hybrids in array - not a complete test of pollinator preference Need to show that hybrids attract mix of pollinator types

Are sympatric (overlapping distribution) in CA

Viable hybrids made from hand-pollinations

Are sympatric (overlapping distribution) in CA Viable hybrids made from hand-pollinations No hybrids seen under natural conditions

Results % of total visits made by bees

Conclusion Prove that corolla traits can determine type of pollinator attracted Pollinator preference can contribute to divergence of angiosperms through reproductive isolation

Lecture Overview Vascular plant diversity Modes of angiosperm speciation Pollination modes and angiosperm diversification Experiments: pollinator-mediated selection on floral traits Conclusions

Summary Animal-pollination mode is correlated with diversification of angiosperms Pollinator preferences can drive floral trait evolution Floral trait evolution in response to pollinator preferences can lead to reproductive isolation (= speciation) Pollinators have contributed to diversification of angiosperms

Archaeofructus