Abstract
ABSTRACTHere, we report on the results of an experimental study that assessed the visitation frequency of wild bees to conspecific flowers with different sized floral guides. UV absorbent floral guides are ubiquitous in Angiosperms, yet surprisingly little is known about conspecific variation in these guides and very few studies have evaluated pollinator response to UV guide manipulation. This is true despite our rich understanding about learning and color preferences in bees. Historical dogma indicates that flower color serves as an important long-range visual signal allowing pollinators to detect the flowers, while floral guides function as close-range signals that direct pollinators to a reward. We initiated the work presented here by first assessing the population level variation in UV absorbent floral guides for conspecific flowers. We assessed two species, Rudbeckia hirta and R. fulgida. We then used several petal cut-and-paste experiments to test whether UV floral guides can also function to attract visitors. We manipulated floral guide size and evaluated visitation frequency. In all experiments, pollinator visitation rates were clearly associated with floral guide size. Diminished floral guides recruited relatively few insect visitors. Exaggerated floral guides recruited more visitors than smaller or average sized guides. Thus, UV floral guides play an important role in pollinator recruitment and in determining the relative attractiveness of conspecific flower heads. Consideration of floral guides is therefore important when evaluating the overall conspicuousness of flower heads relative to background coloration. This work raises the issue of whether floral guides serve as honest indicators of reward, since guide size varies in nature for conspecific flowers at the same developmental stage and since preferences for larger guides were found. To our knowledge, these are the first cut-and-paste experiments conducted to examine whether UV absorbent floral guides affect visitation rates and pollinator preference.
Highlights
A comprehensive, high quality literature exists regarding the sensory and cognitive abilities of bees
We focus on Halictidae, the relatively poorly studied, yet numerically abundant, cosmopolitan generalist pollinators frequently found in urban ecosystems (Dikmen, 2007)
Despite the ubiquity of UV absorbent floral guides in Angiosperms, very little work has addressed the association between pollinator visitation frequency and UV floral guide traits, possibly because these traits were assumed to serve orientation purposes only
Summary
A comprehensive, high quality literature exists regarding the sensory and cognitive abilities of bees. von Frisch, 1914; Daumer, 1956; Daumer, 1958; Backhaus, 1991; Giurfa et al, 1996; Dyer et al, 2008; Dyer et al, 2011; Spaethe et al, 2001). Bees and humans both have trichromatic vision, but bee vision is short wave shifted compared to humans. Data from 43 species of hymenoptera demonstrate maximal receptor sensitivity (l max) at ,340 nm, 430 nm, and 535 nm, respectively (Peitsch et al, 1992; Menzel and Blakers, 1976; Menzel and Backhaus, 1991 and references therein)
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