Meeting Abstract
Floral chemistry characterizing different pollination syndromes suggests that there are some specific floral volatiles with more significance to certain classes of pollinator. For example, the scent associated with flowers within the hawkmoth pollination syndrome is described as ‘white floral’ and often contains nitrogenous volatiles and other characteristic compounds. From this comes the hypothesis that hawkmoths (and other distinctive pollinators) may exhibit stronger olfactory responses to key compounds characterizing their respective pollination syndromes, and this may be due to adaptations in peripheral receptor populations or central olfactory processing. Yet, floral volatiles vary markedly in volatility and differential responses to certain compounds may result from signal intensity rather than sensory adaptations or receptor differences. The predicted vapor pressures of common floral volatiles can range from several kilopascals (~24 mmHg) to less than 1/5th of a single pascal (0.0015 mmHg) at room temperature. This vapor pressure variation translates into a difference of several orders of magnitude in airborne odorant concentrations generated from equimolar solutions. In order to compare responses between olfactory stimuli with different physical properties, the stimuli should be presented at equal concentrations in the vapor phase. Non-standardized stimuli limit the inferences and interpretations that can be drawn from electrophysiological and behavioral experiments. Using methods adapted from dynamic headspace sampling of floral volatiles, we are able to quantify the airborne stimuli created by odorant compounds in order to standardize stimulus intensity and conduct electroantennographic assays (EAGs) to determine how standardization of these olfactory stimuli might change olfactory responses at the peripheral sensory level. We are using this method to carry out comparative tests to determine if the hawkmoths Hyles lineata and Manduca sexta actually do exhibit increased responsiveness to key compounds characteristic of their pollination syndrome.
