THE INVISIBLE HAND OF FLORAL VOLATILES IN POLLINATION ECOLOGY: DOSAGE, CONTEXT AND SIGNAL EVOLUTION

RAGUSO, RA; MORÉ, M; SVENSSON, G

Lisboa

Simposio; 43rd International Symposium on Essential Oils; 2012

OBJECTIVE: Floral volatiles have long been appreciated as pollinator attractants in specialized tropical plants or those engaged in obligate mutualisms (e.g. figs with fig wasps). In contrast, generalized plant-pollinator interactions more commonly studied in ecological or agricultural contexts typically are considered visually-mediated phenomena, with scant reference to floral chemistry. Here I discuss the evidence challenging this perception, focusing on how context determines the ecological functions of plant volatiles. I will use common floral volatiles ? 2-phenylethanol (2PE), dimethyl disulfide (DMDS) and (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) ? to illustrate my thesis. METHODS: Volatiles were analyzed using static (SPME) or dynamic headspace collection coupled with GC-MS, and behavioral bioassays monitoring pollinator responses to flowers whose odors were manipulated using extracts, emittors or traps. RESULTS & CONCLUSIONS: 2PE is common in diurnal wildflowers pollinated by bees. As a low dosage pollen odor, 2PE attracts andrenid bees to Fragaria flowers (1), but at higher dosage in floral nectar, it repels ants and limits bumblebee visits to Polemonium flowers, reducing nectar thievery and optimizing selection on floral shape (2). DMDS is a universal component of deceptive flowers that mimic carrion. When present in diurnal, temperate flowers or boreal mosses, it attracts flies that disperse the plants? pollen or spores (3, 4). However, when DMDS is emitted by nocturnal, nectar rich flowers of Neotropical vines, it attracts bats as pollinators (5). Finally, DMDS is a common herbivore-induced vegetative volatile in maize, cotton and other crop plants, attracting parasitic wasps as an indirect defense. However, DMDS is the primary floral attractant in two specialized systems, a South American bee-pollinated orchid (6) and an obligate North American yucca-yucca moth interaction (7). Concentration, timing and community ! context determine the functional roles of these three common floral volatiles. REFERENCES: 1. TL Ashman et al. (2005) Ecology 86: 2099-2105. 2. C Galen et al. (2011) Am. Nat. 177: 258-272. 3. M Moré et al. (2012) Ann. Bot. (in review). 4. P Marino et al. (2009) Symbiosis 47: 61-76. 5. von Helversen et al. (2000) J. Comp. Physiol. (A) 186: 143-153. 6. A Wiemer et al. (2009) Plant Biology 11: 506-514. 7. Svensson et al. (2011) Oikos 120: 1577?1583.