Intern Project 2009
UC Santa Barbara
Mating System Evolution: Correlations Between Seed Set and Physiology
Self-pollination has evolved from outcrossing repeatedly, yet the selection pressure resulting in such a change remains unclear. Here, we explore drought avoidance type physiological traits and their correlation with fitness in the genera Clarkia, which possesses several selfing-outcrossing sister taxa . If plants are avoiding water stress, we expect them to have high rates of photosynthesis and transpiration resulting in high fitness. Physiological data, photosynthesis and transpiration, were taken on two outcrossing taxa in the field using a Licor infrared gas analyzer where both the selfing and outcrossing species coexist. Seed set was counted in lab from unopened fruits taken from the same plants from which physiological data was taken in the field. The two were then correlated to identify general pattern among outcrossing species in fitness. Because reproduction is generally thought to be a carbon sink, and we expect a positive correlation between photosynthetic rates and seed set. However, water loss in the dry habitats where Clarkia exists may be detrimental to seed production, thus we expect a negative correlation between transpiration rates and seed set. Water use efficiency (WUE) , which is carbon gain over water loss, integrates both photosynthetic and transpiration rates. We expect to see a negative correlation between WUE and fitness if plants are able to avoid water stress. By showing a positive correlation between physiological rates and fitness in outcrossing taxa dwelling within the range of their selfing sister taxa, we hope to indentify historical selection pressures that may have resulted in the change from an outcrossing to a selfing mating system.