Trumpet Flowers of the Sonoran Desert: Floral Biology ofPeniocereusCacti and SacredDatura

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences.The floral biology of night-blooming Peniocereus cacti and Datura plants was studied in North America's Sonoran Desert. In populations of two rare cactus species (Peniocereus greggii and Peniocereus striatus), individual plants bloom synchronously on less than five nights per year and are self-incompatible. In contrast, the abundant Datura discolor and Datura wrightii bloom nearly continuously from spring to autumn and are self-compatible. Flowers of all species studied are visited by hawk moths at dusk and by honeybees and native bees the following morning. Hawk moths have the appropriate behavior and body dimensions to pollinate Peniocereus effectively, but visits are rare. Nonnative honeybees also visit P. greggii and may contribute incrementally to fruit set. Peniocereus and Datura flowers are highly reflective at all wavelengths above 400 nm but lack UV reflectance or contrast. All species studied secrete 10-80 mL of sucrose-rich nectar within flared corollas so deep that moths must land within them, ensuring pollen carriage. These flowers provide rich energetic resources for hawk moths because the caloric content of a single flower would support from 3 to 20 min of hovering flight. Floral scents were more species specific than visual cues because D. discolor and D. wrightii emit complex blends of terpenoid, benzenoid, aliphatic, and nitrogenous scent compounds, whereas flowers of P. greggii produce only eight benzenoid compounds (all of which are present in Datura species) and Peniocereus striatus is scentless. Peniocereus cacti may benefit from sequential mutualism with the more abundant Datura species by way of pollinators nurtured as larvae by Datura foliage and as adults by Datura floral nectar.

Context- and scale-dependent effects of floral CO 2 on nectar foraging by Manduca sexta

“…Instead, our results support the hypothesis that CO 2 acts as an orientation stimulus (Table 1, H A1 ). The CO 2 plume evoked the typical zigzag casting flight pattern indicative of odor-guided behavior in M. sexta (30,47,48) and was slightly more likely to elicit upwind casting flight than was floral odor. These results suggest that floral CO 2 is perceived by M. sexta as an odor, a hypothesis that is consistent with the fact that CO 2 -receptor cells in the LPO project their axons through the suboesophageal ganglion into both antennal lobes (34), the primary centers for the processing of olfactory inputs from the antennae.…”

“…If floral CO 2 levels were ephemeral, insects might use them as more ''honest'' indicators of nectar availability in real time than floral color or scent (2), in much the same way that tarsal secretions are used as flower-marking cues by foraging bees (27,28). Given that CO 2 is a component of ambient air in plant communities, flowers would need to emit amounts that could be detected by the insect with a sufficiently high signal-to-noise ratio.These conditions are met in a night-blooming plant, Datura wrightii [Solanaceae (29,30)], and its primary pollinator, the crepuscular hawkmoth, Manduca sexta (Sphingidae), in the Sonoran Desert. Hawkmoth-pollinated flowers often undergo dramatic bud elongation, nectar secretion, scent biosynthesis, and emission during the 6-12 h before opening (31, 32).…”

“…These conditions are met in a night-blooming plant, Datura wrightii [Solanaceae (29,30)], and its primary pollinator, the crepuscular hawkmoth, Manduca sexta (Sphingidae), in the Sonoran Desert. Hawkmoth-pollinated flowers often undergo dramatic bud elongation, nectar secretion, scent biosynthesis, and emission during the 6-12 h before opening (31,32).…”

Antagonistic effects of floral scent in an insect–plant interaction

“…We tested this idea focusing on linalool, a compound widespread in floral scents (Knudsen et al 2006) and a common constituent of the floral scent of hawkmoth-pollinated flowers (Miyake et al 1998;Raguso & Pichersky 1999). Although a minor component in the D. wrightii flower odour (Raguso et al 2003), linalool is an important FV, mediating nectar foraging in M. sexta (Riffell et al 2009a). In addition, projection neurons (PNs) associated with a female-specific glomerulus in the primary olfactory centres (the antennal lobes, ALs) of M. sexta, which may be involved in the sensory control of oviposition behaviour (Schneiderman et al 1986), respond selectively to (þ)-linalool (Reisenman et al 2004; figure S1 in the electronic supplementary material).…”

Behavioral consequences of innate preferences and olfactory learning in hawkmoth–flower interactions

“…M. sexta has a wide geographic range and typically feeds from a narrow range of moth-adapted flowers (13)(14)(15). In the semiarid grassland of Arizona, M. sexta is a frequent visitor to Datura wrightii (Solanaceae) (16). D. wrightii possesses the typical phenotype of hawkmoth-pollinated flowers: nocturnal anthesis, intense and sweet fragrance, and reflective coloration (16,17).…”