Evolutionary ecology of reproductive isolation between two sympatric Gelsemium species (G.
rankinii and G. sempervirens) in
The following VSU undergraduate students have worked with me on various aspects of this project:
1999-Darrell Alderman, Stephanie Wright, Misty Flantroy;
2000-Dawn Down, Amie Waldron;
2002-Anna Salvador;
2007-Lovie Mansfield
Previous research found that these two species of native vines co-occur but do not hybridize. My research has revealed that the two species share the same pollinator (the blueberry bee) but flower at distinct times (Pascarella 2007-American Journal of Botany). The following topics need to be addressed in order to understand this process:
A) What is the mechanism that controls flowering time for these species? Greenhouse and field studies are needed to address variation in flowering time as this variation appears critical to preventing pollen movements between the species. Greenhouse studies could use the environmental growth chambers and the greenhouses to vary environmental variables such as light, temperature, and water and their effects on flowering. In the field studies, we will plant both species along the natural gradient that defines the habitat of both species (wetland (G. rankiniii) to uplands (G. sempervirens). Ideally, genetic clones of each species would be used to minimize individual genetic variation. The first step in this process is to develop clonally propagated individuals of each species for use in greenhouse and field studies. A potential MS thesis would be to examine the flowering response and associated physiological variables (water potential, photosynthetic rate) to determine the underlying mechanisms regulating this important isolating mechanism.
B) Impact of co-flowering on individual fitness. By manipulating flowering time in the greenhouse, artificial arrays of either pure or mixed species can be developed and effects on individual fitness can be examined. A potential MS thesis here would involve looking at pollinator attraction and movement and pollen delivery and fruit set in pure vs mixed arrays. Because the two species are incompatible, the prediction is that mixed arrays of co-flowering species should show reduced fruit and/or seed set in comparison to pure arrays. However, this will depend on whether pollinators show assortative or non-random movement patterns between species and the effects of pollen clogging on stigma reception and pollen tube growth.
J.B. Pascarella. 2007. Mechanisms of prezygotic reproductive isolation between two sympatric species, Gelsemium rankinii and Gelsemium sempervirens (Gelsemiaceae), in the southeastern United States. American Journal of Botany 94(3): 468-476.