Academic journal article The American Midland Naturalist

Timing Is Everything: Temporal Variation in Floral Scent, and Its Connections to Pollinator Behavior and Female Reproductive Success in Phlox Divaricata

Academic journal article The American Midland Naturalist

Timing Is Everything: Temporal Variation in Floral Scent, and Its Connections to Pollinator Behavior and Female Reproductive Success in Phlox Divaricata

Article excerpt

ABSTRACT.-

The study of floral traits and pollination for the plant genus Phlox has historically been focused on either surveys of general pollinator affinities across the genus or detailed research on pollinator-mediated evolution of floral color in a single species (Phlox drummondii). The purpose of this study was to explore a different kind of trait - floral scent - in Phlox divaricata, a species noted for its strong scent. Specifically, we predicted the diel emission patterns of floral scent might covary with the daily abundance of diurnal moths, identified in a previous study as the most important pollinators in a Konza Prairie population of P. divaricata. Consistent with this prediction, we documented peaks in median floral scent emissions at 1000-1200 and 1930-2130, coinciding with peaks in moth visitation and resulting seed production. Two groups of scent compounds contributed to this pattern; linalool and its associated lilac aldehyde/alcohol compounds (especially lilac aldehyde B) contributed a greater proportion to scent at 1000-1200, while aromatic compounds (including benzaldehyde and benzyl acetate) contributed a greater proportion to scent at 1930-2130 and other afternoon time periods. These volatiles are known floral attractants for several lepidopteran pollinators, including noctuid moths. However, there is an additional peak in pollinator abundance (Hemaris diurnal hawkmoths) and seed set at a time when scent production is relatively low (1400-1600) suggesting additional factors mediate both pollinator behavior and floral volatile emissions. Future studies of P. divaricata should test for the presence of destructive floral enemies that might be attracted by floral volatiles during mid-afternoon periods, as well as the importance of visual floral traits (color, shape) in attracting diurnal moths, an important functional group of pollinators that has received minimal attention in North America.

INTRODUCTION

Studies of unique floral forms and functions for a number of different plant species have led to a greater understanding of the evolutionary history of relationships between plants and pollinators; such relationships have resulted in the great diversity of angiosperms we see today. One particular group that has received a great deal of interest is Phlox (ca. 60 species), the largest genus in the family Polemoniaceae (Wherry, 1955; Grant, 1959). Because members of this family are visited by a diversity of pollinator guilds (bees, flies, bats, and hummingbirds; Grant and Grant, 1965), the group has been the focus of numerous pollination studies (Robertson, 1891; Erbe and Turner, 1962; Levin, 1963, 1969; Grant and Grant, 1965; Levin and Kerster, 1967a, b; Strakosh and Ferguson, 2005; Wiggam and Ferguson, 2005). One intriguing outcome of such studies has been that despite high overall pollinator diversity, butterflies and moths are dominant visitors in many species.

The propensity for lepidopteran pollination in Phlox is not surprising given the basic floral form found in the genus. Flowers are salverform with a narrow tube that typically restricts nectar access to long-tongued insects (e.g., those with tongues equaling or exceeding floral tube length). Additionally, some species exhibit reverse herkogamy (stigma is inserted deep within the floral tube and the anthers are positioned above the stigma; Wherry, 1955), which is common in lepidopteran-pollinated plants (Barrett, 2003), including many in the Polemoniaceae (Kulbaba and Worley, 2012). Phlox species also show variation in floral pigment, both within and among species (Grant and Grant, 1965); this includes white and blue/lavender variants that are attractive to lepidopterans (Kelber et ai, 2003; Balkenius et al, 2006). Finally, distinct species-specific floral scent profiles have also been found for several Phlox species (Wiggam-Harper, 2003; Junker et al, 2011; Majetic and Sinka, 2013; Majetic et al, 2014). Many of these profiles are complex, containing compounds that are attractive to lepidopterans (such as linalool and lilac compounds; Knudsen and Tollsten, 1993; Dotted and Jürgens, 2005) and compounds known to attract other classes of pollinators (Dobson, 2006) ; such variety may account for reports of visits by other insect pollinator groups in addition to lepidopterans. …

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