The effect of mammalian herbivory on inflorescence architecture in ornithophilous Babiana (Iridaceae): Implications for the evolution of a bird perch

 Premise of the study: The showiness of fl displays is usually explained as an adaptation to attract pollinators. However, selection for less attractive displays imposed by non-pollinating agents, particularly herbivores, may balance pollinator-driven selection for highly visible infl orescences. We investigated whether infl orescence architecture, particularly the unusual groundlevel fl owering associated with a specialized bird perch in Babiana ringens may have originated, in part, as an adaptive response to mammalian herbivory.  Methods: We measured levels of herbivory by antelope in populations of B. hirsuta , the putative sister species of B. ringens , which possesses the likely ancestral form of infl orescence architecture. To test for position-dependent effects of herbivory on fl owers, we compared the herbivory rates and seed production of manipulated infl orescences in a fi eld experiment. We predicted that fl owers at the base of infl orescences would suffer less herbivory than those in apical positions.  Results: We found herbivore damage to flin 50% of naturally occurring B. hirsuta plants. Manipulated infl orescences with only basal fl owers, and consequently similar infl orescence architecture to B. ringens , experienced signifi cantly lower herbivory and higher seed set than infl orescences manipulated to have only apical fl owers.  Conclusions: Our results are consistent with the hypothesis that position-dependent herbivory on infl orescences could have played a role in the evolution of infl orescence design. More specifi cally, position-dependent herbivory may have selected for the loss of apical fl owers. Position-dependent herbivory may have contributed toward the evolution of a naked infl orescence axis, a structure that characterizes B. ringens and functions as a bird perch facilitating cross-pollination by sunbirds.