Format: ORAL

Geoffrey T. Broadhead1,2, Robert A. Raguso1

1 Cornell University, Ithaca, USA 2 University of Florida, Gainesville, USA

Hawkmoths are important pollinators worldwide, whose powerful dispersal flights can promote gene flow between geographically distant plant populations. That same flight capacity generates high energetic demands, and hawkmoths are known to maximize caloric intake in the face of thermal, osmoregulatory and biophysical constraints. Thus, hawkmoth-pollinated flowers tend to secrete copious quantities of relatively dilute (15-30%) sugar solutions at anthesis, just as they emit strong fragrances known to attract hawkmoths from a distance. One surprising feature of such fragrances is the presence of nitrogenous aldoximes, volatile compounds derived from essential amino acids (LEU, ILE, VAL, and PHE). Aldoximes are uncommon fragrance components in day-blooming plants and are better known for their roles in the indirect defenses of wounded poplar foliage, or as precursors to direct defenses such as mustard oils and cyanogenic glycosides. Nevertheless, they have evolved in dozens of angiosperm families with night-blooming flowers, from Darwins star orchid to jasmines and gingers. Given that aldoximes are derived from amino acid precursors, we explored their potential to function as volatile index signals unfakeable indicators of the presence of amino acids in nectar, using the night-blooming flowers of Oenothera flava and Datura discolor as model systems. First, we tested whether volatile aldoximes are correlated with nectar amino acids, either naturally or under soil fertilizer manipulation, using GC-MS and HPLC, respectively. Next, we designed behavioral assays to test whether flower-nave hawkmoths (Hyles lineata) are attracted to aldoximes derived from LEU and ILE in a nectar-feeding context. Finally, we used behavioral assays to test whether hawkmoths prefer nectars with amino acids, and whether such fortified nectars provide additional fitness benefits to the moths. Our findings suggest an important role for N metabolism as a non-caloric component of floral advertisement and reward in moonflowers pollinated by hawkmoths.