To further test their idea, De Waal and colleagues conducted a field experiment with B. hirsuta in which they manipulated flower position along the stalk they removed side branches in plants so that they displayed either flowers only at the top or only at the bottom of the stems (the latter resembling the display of B. ringens). Using cages, they then excluded herbivores from half of the treatments.
"Our most important result," De Waal stated, "is that flowers at the tips of stems were eaten by browsing antelope, whereas flowers at ground-level were consistently ignored." Notably, this was even the case for plants that were not protected from herbivores by cages, yet were manipulated to have only ground-level flowers.
"Significantly, plants with only ground-level flowers produced more seeds," she said. "This means that plants that manage to escape damage by herbivores also have higher reproductive success, and this may be the reason why B. ringens evolved its unusual ground-level flowers."
Moreover, Anderson adds, "The overwhelming herbivore preference for plants with only apical flowers indicates why plants like B. ringens, with basal flowers, could have evolved while plants with only apical flowers would be maladapted."
"Our results indicate that in addition to pollinators, herbivores can also be important selective agents on inflorescence architecture," concluded Anderson. "This is significant because most scientists have attributed variation in floral display to selection by pollinators and the importance of herbivores is often forgotten."
|Contact: Richard Hund|
American Journal of Botany