Patterns of Pollination and Seed Predation Limit Scotch Broom (Cytisus scoparius L.) Robert Bode, PhD Saint Martin’s University Our Well-Known Nemesis
• Cytisus scoparius L.
• Noxious, invasive, toxic, etc.
• Self-incompatible
• Biocontrols introduced Self-Incompatibility
• Unusual in an invasive
• Goldenrod in Britain and Japan
• Kudzu may evolve selfing (Steven et al 2013)
• Invader in need of a pollinator Pollinator limitation
• Scotch broom is pollinator limited (Parker 1997)
• But it seems to be doing just fine…
• Do urban structures limit pollination in broom? Pollinator selection on Floral Traits in Scotch broom • If pollinators are limiting broom, their choice should exert selective pressure
• We may see pollinator choice
• Footprint of evolution past Selection along a gradient
• Urban patches may be distinct samples
• Gradient along Martin Way
• Will bees prefer certain plants? • Will flowers be different sizes? Flower size varies, but without a pattern
Malo and Baonza 2002 • If selection is present, it has not led to local adaptations
• Gene flow may homogenize the population 26
25 24 23 22 • Variation is higher within sites 21 20 than in Malo and Baonza’s entire 19 18
Banner Width (mm) Width Banner study! 17 16 0 5 10 15 20 25 30 Site number Selection on flowers differs between urban and rural populations
Slope of the line as a selection gradient: pollination as a proxy for fitness
Urban Rural Site 31 Site 1
0.9 0.6
0.8 0.5 0.7 0.6 0.4 0.5 y = -0.0537x + 1.294 y = 0.0613x - 0.734 0.3
0.4
Pollinated (Fitness) Pollinated Pollinated (Fitness) Pollinated 0.3 0.2 0.2 0.1
0.1
Proportion Proportion Proportion Proportion 0 0 17 19 21 23 25 19 19.5 20 20.5 21 21.5 22 22.5 23 Banner width Banner Width Selection differs between Urban and Rural Sites 0.12 • Plants with large flowers are
0.08 pollinated more in the city
0.04
P<0.01 0 • Reverse is true in rural areas
Selection gradient Selection -0.04
-0.08 • Why?
-0.12 Urban Rural Biocontrols are ineffective in Scotch broom
Exapion fuscirostre • Between 70% and 99.9% of seeds must be eaten to reduce population (Parker 2000)
• In conjunction with bee die-off,
seed predators can lead to Bruchidius villosus broom extinctions (Paynter 2010)
Image Credit: Kerbtier.de Seed Predation in Urban Environments
80 70 60 Bode and Gilbert in press 50 • Seed predators are our best 40 urban option for weed control 30 20 10
Percent Seed Predation Seed Percent 0 0 1 2 3 4 5 • Arthropods are limited by urban Log (patch Size) obstacles (Faeth and Kane 1978, Bode and Maciejewski 2014)
Urban vs. Rural Seed Predation
• How do beetle and weevil impacts on Scotch broom vary between urban and rural environments?
• (15*2)*15*10= large sample!
Fitness is Pollination plus Seed Survival
UrbanRural Plants have Higher Fitness Rural Plants Suffer Less Seed Predation 8 1 7.9
0.95
7.8 7.7 7.6 0.9 1 7.5 p=0.07 7.4 0.9 0.85 p=0.006 7.3 0.8
Mean Seeds per Pod per Seeds Mean 0.7 7.2 0.8 0.6
7.1 Eaten ofSeeds Proportion 0.5 0.75 7 p=0.01 0.4 Urban Rural 0.3 0.7 0.2 Urban Rural
0.1
Mean UNEATEN Seeds per Pod per Seeds UNEATEN Mean
0 Urban Rural Seed Predators are Not Homogenously Spread
Weevils prefer the Countryside There is Variability between Sites 0.2 1
0.18 0.9
0.16 0.8 0.7 0.14 0.6 0.12 0.5 0.1 p=0.01 0.4 0.08 0.3 0.06
Relative Damage by Beetles by Damage Relative 0.2 Proportion eaten by weevils by eaten Proportion 0.04 0.1
0.02 0
7 8 9
11 12 13 14 15 18 19 31
R1 R2 R4 R5 R6 R7 R8 R9 R15 0 R11 Urban Rural Site What have we found?
Pollinator selection on Scotch broom Biocontrol Impact on Scotch broom • Big flowers in the city • The beetles are doing a good job
• Gene flow may homogenize • Weevils and beetles differ in populations distribution
• Balancing selection? • More control is needed in rural areas (Parker 2000)
30
28 26 24 22 Coming soon… 20
18 R² = 0.2441 Banner Width (mm) BannerWidth 16 0 500 1000 1500 2000 2500 3000 Elevation (feet a.s.l.) Germination experiments Elevation experiments • Does smoke influence broom • There is a pattern of flower size germination? (Danner) along an elevation gradient They see me evolvin’ • Do local plants release • What is causing this? allelochemicals? (Emily) They hatin’ • Murdock Natural Sciences Grant Proposal Many thanks
• Saint Martin’s University (Funding, lab space, grounds) • My undergraduate research assistants (Nathan and Rebecca) • My minions (Danner and Emily) • Many landowners who could care less what I did to their weeds • Jenn Andreas, Eric Coombs
• You, the next time you pull out some broom!