Sahli, H. F. 2006. Generalization in plant pollination systems and its effect on floral evolution within and among populations of wild radish (Raphanus raphanistrum). Ph.D. Dissertation, Michigan State University, East Lansing, Michigan, USA.
While specialists are thought to be well adapted to their resources, generalists are thought to be a jack of-all-trades but master of none. However, few studies have examined how selection by multiple resources influences the evolution of morphnological traits in generalists. As most plants are dependent upon pollinators for reproduction, pollinators are important, and often essential, plant resources. I examined the degree of generalization in wild radish (Raphanus raphanistrum) nd how selection by multiple pollinators influences adaptation to each toxon individually, both within and among populations.
Although previous studies of generalization in plant-pollination systems have focused primarily on estimates of species richness, pollinators exhibit great variation in visitation rates. I found that diversity indices, which take into account both species richness and evenness, provide a more useful estimate of pollinator generalization. I characterized generalization in the pollinator assemblage of the widespread agricultural weed, wild radish, and studied how pollinators differed in their selection on several floral traits. Although wild radish is effectively pollinated by at least 14 pollinator genera, few of these taxa actually selected on floral traits. My findings suggest that wild radish is able to adapt to a subset of its pollinators without trading off the ability to effectively use other taxa.
Finally, I examined how selection and drift have contributed to differentiation of floral and phonological traits of wild radish by comparing estimates of population differentiation in quantitative traits (Qst) to population differentiation in allele frequencies (Fst). I found that differences in most floral traits among populations can be explained by drift alone. I also found that life history traits such as ovule number and flowering time were under strong divergent selection across populations, suggesting life history traits may have been important in colonization and adaptation to new habitats.
Overall, my results indicate that wild radish has successfully evolved to use many pollinators to effect reproduction, that it can adapt to a subset of these pollinators without trading off the ability to use others effectively, and that its success as a generalist my be one reason for its successful invasion in many non-native environments.Sign in to download PDF back to index