Evolution of Plant–Pollinator Relationships, ed S. Patiny. Published by Cambridge University Press. © Cambridge University Press 2012. 9 Why are lora l signals complex? An outline of functional hypotheses Anne S. Leonard Center for Insect Science / Department of Ecology and Evolutionary Biology, University of Arizona Anna Dornhaus Center for Insect Science / Department of Ecology and Evolutionary Biology, University of Arizona Daniel R. Papaj Center for Insect Science / Department of Ecology and Evolutionary Biology, University of Arizona 9.1 Introduction Plants produce a remarkable variety of displays to attract animals that transfer pollen. hese loral displays are usually complex, broadcasting various combin- ations of visual, olfactory, gustatory, tactile, and thermal stimuli (Raguso 2004a). Even acoustic stimuli may be involved, as in the case of structural nectar guides used by echolocating lower-feeding bats (von Helversen and von Helversen 1999). Yet these sensorially complex advertisements likely evolved from an ancestor that primarily transmitted only chemicals, serving a defensive function (Pellmyr and hein 1986). he subsequent ampli icat ion and elaboration of loral stimuli therefore ofers an intriguing opportunity to study signal evolution. However, at present, we know surprisingly little about why loral displays consist of so many elements. his contrasts wit h progress in other areas: recently, researchers study- ing topics as diverse as sexual selection, warning displays, animal learning, and 9780521198929c09_p261-282.indd 261 7/26/2011 7:51:04 PM