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Food for Sex: or how to attract a pollinator.
 
 
Authors          Audiences          Overview           Materials          Resources           Future Directions
 

 


Authors


Joyce Cadwallader
Saint-Mary-of-the-Woods College


Brian White
University of Massachusetts


Christine Tuaillon
Nassau Community College

 
   
 


Possible Audiences:

Introductory Biology Course Genetics for non-majors  

 
 


Brief Overview:

Two sister species of monkey flower are pollinated by different pollinators; this difference is a major factor in their reproductive isolation. One species Mimulus cardinalis has small red flowers with high nectar levels and is pollinated by hummingbirds while the other species, Mimulus lewisii, has large pink flowers with low levels of nectar and is pollinated by bumblebees. See pictures below:

Although the mechanism of species maintenance is clear, what is less clear is the process that led to the speciation in the first place. We have developed an Excel spreadsheet that models the interaction of the two pollinators with monkeyflowers that have varying color and nectar production phenotypes. Users can specify:
  • the starting color and nectar genotypes of the population
  • the color and nectar preferences of the birds
  • the color and nectar preferences of the bees
  • the relative visitation rates of the birds and bees
The spreadsheet then runs a standard Hardy-Weinberg simulation for 20 generations under the specified conditions and plots the results. This model follows the frequencies of the alleles in two "gene pools": the alleles carried by the bees and the alleles carried by the birds. At each generation, each pool is calculated, used to produce offspring, and the resulting offspring are then pooled.

One example is shown below:

In this simulation:
  • Starting Population: The population is mostly "bee type" (Pink/Low-nectar Pl) with a few Red and High-nectar alleles in the population. This models the original state (M. lewisii) after some mutations have occurred and started to increase in the population.
  • Flower Preferences: The bees prefer M. lewisii (Pl)primarily, with some possibility to visit the other phenotypes; the hummingbirds prefer M. cardinalis (rH), with some possibility to visit the other phenotypes as well.
  • Pollinator Visits: The total pollination success for bees and birds are equal.
  • Results: the population evolves from one species into two. This is shown by:
    • M. lewisii (yellow line) drop in frequency and is replaced by a population that is a roughly equal mixture of M. lewisii (yellow) and M. cardinalis (red).
    • The hybrids (green and blue lines) are eliminated from the population, indicating that cross-pollination is not occurring at a significant rate.
    • The degree of difference between the alleles carried by the bees and by the birds ("Sep"; dashed black line) increases, showing the lack ofmixing in the two gene pools.
The lab manual contains a series of exercises that explore the relevant parameters in the model and their connection to pollination and speciation in the real world.  

 
   
 


Project Materials:

  • Laboratory Manual (word format)
  • Mac or PC with Excel worksheet "MimulusPollination.xls"
  • PowerPoint presentation from workshop
 

 
 


Resources and References:

  • Bradshaw HD. And Schemske DW. 2003. Allele substitution at a flower colour locus produces a pollinator shift in monkeyflowers. Nature 426: 176-178
  • Darwin C. 1862. On the various contrivance by which British and foreign orchids are fertilized by insects. London. John Murray. pp 197-98
  • Hokche O. and Ramirez N. 1990. Pollination Ecology of Seven species of Bauhinia L. (Leguminosae: Caesalpinioideae), Annals of the Missouri Botanical Garden, 77 (3): 559-572
  • Ramsey, J, Bradshaw, HD, and Schemske, DW 2003. Components of Reproductive Isolation between the Monkeyflowers Mimulus lewisii and M. cardinalis (Phyrmaceae). Evolution 57(7):1520-1534
  • Russel G. 2003. Orchids of South Africa. Yearbook of the South African Orchid Council. pp 59-65
  • Schemske DW. and Bradshaw HD. 1999. Pollinator preference and the evolution of floral traits in monkeyflower (Mimulus). PNAS 96 (21): 11910-11915
  • Wallace AR. 1867. Creation by Law. Quartely Journal of Science, volume 4 (October 1867)
 

 
   
 


Future Directions:

  • Further development of exercises.
  • Connection to Bee Visit, a simulation of pollination.
 

 
 


Attachments


- MimulusPollination.xls
- mimulus_simulation.jpg
- MumulusPresentation.ppt
- Sample lab exercise using Mimulus Pollination .doc