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Lecture Overview • • • • • Speciation in vascular plants Plant-pollinator origins Insect and angiosperm diversification Proving pollinator-mediated speciation Empirical evidence for pollinator-mediated selection on floral traits • Empirical evidence for pollinator-mediated speciation Margaret Mee Margaret Mee (1909-1988) (1909-1988) Margaret Mee Margaret Mee Margaret Mee (1909-1988) (1909-1988) (1909-1988) Empirical Evidence for Pollinator-mediated Diversification In Angiosperms Lecture Overview • • • • • Speciation in vascular plants Plant-pollinator origins Insect and angiosperm diversification Proving pollinator-mediated speciation Empirical evidence for pollinator-mediated selection on floral traits • Empirical evidence for pollinator-mediated speciation Common Modes of Speciation in Angiosperms • Mechanical barriers to gene flow (e.g. separation by new mountain range; long-distance dispersal to island) Common Modes of Speciation in Angiosperms • Mechanical barriers to gene flow (e.g. separation by new mountain range; long-distance dispersal to island) • Change in ploidy level (diploid tetraploid) Common Modes of Speciation in Angiosperms • Mechanical barriers to gene flow (e.g. separation by new mountain range; long-distance dispersal to island) • Change in ploidy level (diploid tetraploid) • Pollinator-mediated reproductive isolation – changes in floral traits driven by pollinator preference Lecture Overview • • • • • Speciation in vascular plants Plant-pollinator origins Insect and angiosperm diversification Proving pollinator-mediated speciation Empirical evidence for pollinator-mediated selection on floral traits • Empirical evidence for pollinator-mediated speciation Origins of plant-pollinator interactions • Dates back ~ 300 million years to cycads Origins of plant-pollinator interactions • Dates back ~ 300 million years to cycads • Cycads (gymnosperms) pollinated by weevils Origins of plant-pollinator interactions • Dates back ~ 300 million years to cycads • Cycads (gymnosperms) pollinated by weevils • Male and female cones thermogenic - emit attractive scent Origins of plant-pollinator interactions • Dates back ~ 300 million years to cycads • Cycads (gymnosperms) pollinated by weevils • Male and female cones thermogenic - emit attractive scent • Weevils, feed, mate, lay eggs in male cones Origins of plant-pollinator interactions • Dates back ~ 300 million years to cycads • Cycads (gymnosperms) pollinated by weevils • Male and female cones thermogenic - emit attractive scent • Weevils, feed, mate, lay eggs in male cones • Offspring visit female cones Lecture Overview • • • • • Speciation in vascular plants Plant-pollinator origins Insect and angiosperm diversification Proving pollinator-mediated speciation Empirical evidence for pollinator-mediated selection on floral traits • Empirical evidence for pollinator-mediated speciation Diversification of insects and angiosperms • Earliest angiosperms ~130 mya; followed by exponential in angiosperm species diversity Archaeofructus Diversification of insects and angiosperms • Earliest angiosperms ~130 mya; followed by exponential in angiosperm species diversity • Bird and bee radiation occurred simultaneously Diversification of insects and angiosperms • Earliest angiosperms ~130 mya; followed by exponential in angiosperm species diversity • Bird and bee radiation occurred simultaneously • Angiosperm diversification fastest in animalpollinated lineages Diversification of insects and angiosperms • Earliest angiosperms ~130 mya; followed by exponential in species diversity • Bird and bee radiation occurred simultaneously • Angiosperm diversification fastest in animalpollinated lineages • Angiosperm diversity driven by pollinators? Lecture Overview • • • • • Speciation in vascular plants Plant-pollinator origins Insect and angiosperm diversification Proving pollinator-mediated speciation Empirical evidence for pollinator-mediated selection on floral traits • Empirical evidence for pollinator-mediated speciation Proving pollinator-mediated speciation • Demonstrating speciation by pollinators is difficult Proving pollinator-mediated speciation • Demonstrating speciation by pollinators is difficult – many closely-related taxa don’t interbreed Proving pollinator-mediated speciation • Demonstrating speciation by pollinators is difficult – many closely-related taxa don’t interbreed • Difficult to acquire empirical evidence to satisfy skeptic Proving pollinator-mediated speciation • Demonstrating speciation by pollinators is difficult – many closely-related taxa don’t interbreed • Difficult to acquire empirical evidence to satisfy skeptical • Can it be demonstrated? Basics of plant/pollinator interaction • Many pollinators seek maximum reward per unit of effort (= optimal foraging) Basics of plant/pollinator interaction • Many pollinators seek maximum reward per unit of effort (= optimal foraging) – short search time – short flower handling time – high reward Basics of plant/pollinator interaction • Many pollinators seek maximum reward per unit of effort (= optimal foraging) – short search time – short flower handling time – high reward • Plants benefit from reliable and efficient pollinators Basics of plant/pollinator interaction • Many pollinators seek maximum reward per unit of effort (= optimal foraging) – short search time – short flower handling time – high reward • Plants benefit from reliable and efficient pollinators – pollen not wasted on wrong flowers – correct placement of pollen in flower Basics of plant/pollinator interaction • Many pollinators seek maximum reward per unit of effort (= optimal foraging) – short search time – short flower handling time – high reward • Plants benefit from reliable and efficient pollinators – pollen not wasted on wrong flowers – correct placement of pollen in flower • Design experiments to exploit these phenomena Proving Pollinator-mediated Speciation • Step 1 - prove pollinator preference (e.g. flower size, color) can cause floral trait evolution Proving Pollinator-mediated Speciation • Step 1 - prove pollinator preference (e.g. flower size, color) can cause floral trait evolution • Step 2 - demonstrate that floral trait evolution leads to reproductive isolation via pollinator preferences Lecture Overview • • • • • Speciation in vascular plants Plant-pollinator origins Insect and angiosperm diversification Proving pollinator-mediated speciation Empirical evidence for pollinator-mediated selection on floral traits • Empirical evidence for pollinator-mediated speciation Two Important Studies • Polemonium viscosum (alpine skypilot) and bumblebees (Galen, 1996) Corolla tube width = 16 mm Timberline 11,000 ft. Corolla tube width = 18 mm Alpine - 12,000 ft. Corolla tube width = 16 mm Timberline 11,000 ft. = 11% difference in corolla tube width Corolla tube width = 18 mm Alpine - 12,000 ft. Corolla tube width = 16 mm Timberline 11,000 ft. What explains corolla tube width difference? = 11% difference in corolla tube width Corolla tube width = 18 mm Alpine - 12,000 ft. Corolla tube width = 16 mm Timberline 11,000 ft. What explains corolla tube width difference? Solitary bees Corolla tube width = 18 mm Alpine - 12,000 ft. Corolla tube width = 16 mm Timberline 11,000 ft. What explains corolla tube width difference? Bumble bees QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Solitary bees Corolla tube width = 18 mm Alpine - 12,000 ft. Corolla tube width = 16 mm Timberline 11,000 ft. 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 Visits/ flower/ hr. Mean corolla tube width Experiment Results Visits/ flower/ hr. Mean corolla tube width Wider Flowers = More Pollen Export Experiment Results Seed set/ flower Visits/ flower/ hr. Mean corolla tube width Optical Density More red Wider Flowers = More Pollen Export Less red Experiment Results Seed set/ flower Visits/ flower/ hr. Mean corolla tube width Optical Density More red Wider Flowers = More Pollen Export Less red Redder Flowers = More Seed Conclusions • Floral traits can determine level of pollinator attraction • Differential foraging by pollinators linked to differential plant reproductive success Lecture Overview • • • • • Modes of speciation in vascular plants Origins of plant-pollinator interactions Diversification of insects and angiosperms Proving the pollinator-mediated speciation story Empirical evidence for pollinator-mediated selection on floral traits • Empirical evidence for pollinator-mediated speciation Reproductive isolation in columbine Aquilegia pubescens Aquilegia formosa Reproductive isolation in columbine Note - viable hybrids from hand pollination Aquilegia pubescens Aquilegia formosa 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 • Reproductive isolation achieved through pollinator preference based on corolla morphological differences Any problems with this study? 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 • Improvement - Mimulus cardinalis (hummingbird) and Mimulus lewisii (bumblebee) (Schemske and Bradshaw, 1999) • Are sympatric (= overlapping distribution) • Are sympatric (= overlapping distribution) • Viable hybrids made from hand-pollinations • Are sympatric (= overlapping distribution) • Viable hybrids made from hand-pollinations • No hybrids seen under natural conditions Results % of total visits made by bees 90 80 70 60 50 40 30 20 10 0 M. lewisii Hybrids M. cardinalis Conclusion • Prove that corolla traits can determine pollinator type • Pollinator preference can lead to divergence of angiosperms through reproductive isolation Lecture Summary • Insect pollination first in gymnosperms, but developed in 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 Insect Pollination and Flowering Plant Species Diversification • Flowering plant families that are insect-pollinated tend to have high degree of speciation (e.g. orchids) • Pollinators likely have been a source of speciation in flowering plant families (e.g. Mimulus)
