JOBNAME: No Job Name PAGE: 1 SESS: 9 OUTPUT: Thu Mar 22 19:04:23 2012 SUM: 9A19A5F0 /v2451/blackwell/journals/psbi_v0_i0/psbi_375 Ultraviolet reflectance mediates pollinator visitation in Mimulus guttatus JASON M. RAE and JANA C. VAMOSI Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada Abstract Floral colors are widely believed to be an adaptation to attract pollinators. Recently, our understanding of floral reflectance has broadened to include colors that are beyond the spectrum that human eyes can perceive (such as ultraviolet (UV) reflectance), yet we still know relatively little about which plant species reflect UV light or its effectiveness in attracting pollinators. We investigated the effect of UV reflectance in Mimulus guttatus in a number of different populations in British Columbia, Canada. We found that M. gut- tatus had distinct regions of the corolla where UV light was reflected and absorbed. When we manipulated the degree of contrast between the reflection and absorption area, we found that pollinator visitation was severely disrupted, in terms of frequency and forag- ing patterns observed. Despite the bright yellow (bee-green) coloration and visible nectar guides in M. guttatus, we conclude that UV reflectance is critical in pollinator attraction. Keywords: floral constancy, geographical variation, Mimulus guttatus, pollinator attraction, UV reflectance. Received 7 June 2001; revision received 15 December 2001; accepted 8 January 2012 Introduction The vast majority of flowering plants (~80–90%) employ insects, birds, and bats to transport and deposit pollen on the stigma of conspecifics (Ollerton et al. 2011). Floral color represents one of the key avenues by which plants advertise their rewards to pollinators, affecting the attrac- tion of different functional groups of pollinators (Fenster et al. 2004) as well as influencing the floral constancy of visitation (Gumbert et al. 1999; Gegear 2005; Gegear & Burns 2007). Investigating the importance of floral color to the reproductive ecology of a particular plant species or the community ecology of coflowering species (McEwen & Vamosi 2010) is complicated, however, by the fact that many plant species reflect in the ultraviolet (UV) part of the spectrum, which many pollinators can perceive but humans cannot. Investigations of floral color that incor- porate the detection of UV light reflectance of petals, sepals, and tepals is thus necessary to refine our under- standing of how selection has operated on these advertis- ing structures in different flowering plant communities. The metaphor of a busy marketplace with vendors (the plants) and customers (the pollinators) operating transac- tions for goods and services has been applied to plant– pollinator relationships (Chittka & Schurkens 2001). From the pollinator’s perspective, optimal foraging is achieved if they are able to distinguish between species of flowers that they have previously learned contain suitable nectar (Leonard et al. 2011), and floral constancy can result from a pollinator’s focus to obtain the “best bargain” for their effort investment (Chittka & Schurkens 2001). From the plants’ perspective, it is advantageous to avoid cross- pollination with incompatible species of flowering plants by facilitating conspecific visitation patterns of the polli- nators (Flanagan et al. 2009). This goal of generating “cus- tomer loyalty,” or floral constancy, can be accomplished in many ways, most notably by visual differences between different species of flower as well as morphological dif- ferences and complexity of nectar access (Wilson & Stine 1996). Because insect pollinators use these visual senses to identify and locate the flowers they forage on, these flowers must be easily distinguishable from the surround- ing environment (Spaethe et al. 2001). Most hymenopterans have trichromatic vision that rec- ognizes ultraviolet (UV) light with peak sensitivity at 340 nm, blue light at 430 nm and yellow light at 535 nm Correspondence: Jana C. Vamosi Email: jvamosi@ucalgary.ca Plant Species Biology (2012) ••, ••–•• doi: 10.1111/j.1442-1984.2012.00375.x © 2012 The Authors Journal compilation © 2012 The Society for the Study of Species Biology 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70