Research Interests
       I am generally interested in genetic correlation and how different mechanisms of correlation have variable implications for predicting evolution. Pleiotropy or gametic phase disequlibrium may cause genetic correlation but only pleiotropy has the potential to form a long term constraint to adaptive evolution.  Surprisingly few studies have looked at the underlying mechanisms of correlation  One method of determining the mechanism of trait correlation is to study traits in which hypotheses about pleiotropic correlations can be made on the basis of genetic architecture. 
To this end, my thesis looks at the role of flavonoids in Tradescantia ohiensis (Commelinaceae). 

My System
     I want to determine if the incredible diversity of flower color I observe in natural populations is maintained by spatially variable selection and/or opposing selection from multiple agents.  Most red, violet, and blue flowers are colored by anthocyanins.  The biochemical synthesis of anthocyanins is a terminal step in flavonoid synthesis.  Many colorless precursors of anthocyanins (such as flavones and flavonols) accumulate in leaf tissue, and response to selection on foliar chemistry may balance response to selection on floral pigmentation.
     The first step in this project is to identify traits that are correlated with flower color and the adaptive value of those suites of traits. Anthocyanin expression in juvenile leaves may protect developing photosystems from oxidative damage.


anthocyanidin
     Damage caused by Lygus spp. (Miridae) and Lema collaris (Chrysomelidae), herbivores of T. ohiensis. Herbivore defense may be tied to flower color if pigment precursors, such as flavones, affect palatibility. 


flavone

Motivation

 Pollination biologists increasingly appreciate that floral trait evolution may be shaped by indirect selection.  Floral flavonoids are an excellent system for the study of indirect selection.  While the ubiquity of flavonoids has long been recognized, their role in a myriad of plant functions has been elucidated only recently and underlying genetics.

An example of a pollination-defense tradeoff:

     In the spring ephemeral Claytonia virginica, flower color is negatively correlated with herbivore defense. 
 

Frey, F. M. 2004. Opposing natural selection from herbivores and pathogens may maintain floral-color variation in Claytonia virginica (Portulacaeae). Evolution 58: 2426-2437.
Flavonoids have also been implicated in stress tolerance in many species.
A few examples:
Coberly, L. C., and M. D. Rausher. 2008. Pleiotropic effects of an allele producing white flowers in Ipomoea. Evolution. 62: 1076-1085.

Warren, J., and S. Mackenzie. 2001. Why are all colour combinations not equally represented as flower-colour polymorphisms. New Phytologist 151:237-241.

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