Dissecting pollinator responses to a ubiquitous ultraviolet floral pattern in the wild

Abstract

Summary1. Colour patterns on flowers can increase pollinator visitation and enhance foraging behaviour. Flowers uniform in colour to humans, however, can appear patterned to insects due to spatial variation in UV reflectance on petals. A UV 'bullseye' pattern that is common among angiosperms -UV-absorbing petal bases and UV-reflective apices -purportedly functions as a nectar guide, enhancing pollinator orientation and experimental evidence suggests that UV reflectance increases floral apparency to pollinators. 2. We test the pollinator-attracting and pollinator-orienting functions of floral UV pattern and UV reflectance under natural conditions. Specifically, we address whether UV reflection alone, or UV pattern influences small bee and syrphid fly attraction rates (approaching, landing and foraging visits), foraging rates, and likelihood of foraging and orienting to the centre of flowers, using Argentina anserina, a species whose flowers exhibit variability in the size of the UV bullseye. We manipulated UV properties while maintaining uniformly yellow petals to create three phenotypes -uniformly UV-absorptive, uniformly UV-reflective, and inversed bullseye (reflective bases and absorptive apices) and compared insect visitation and behaviour to control flowers with the common UV bullseye phenotype. 3. The presence of UV pattern increased attraction rates by both bees and syrphid flies relative to either fully UV reflective or absorptive flowers. However, only in the inverse array did the bullseye phenotype elicit higher foraging rates than the test flower. Neither the presence of pattern, nor the reversal of the common pattern influenced the likelihood of pollinator foraging or orientating to the flowers' centre during a visit. 4. We provide some of the first evidence to suggest that flowers with spatial variation in UV reflectance may be more conspicuous to insects than those with petals that uniformly absorb or reflect UV, all of which are naturally occurring phenotypes. Further, we verify that the most common UV pattern in nature increases insect attraction and foraging rate relative to the inverse pattern. Results confirm a distance apparency function of the UV bullseye, but we argue for reconsideration of the notion that pollinators benefit from this ubiquitous floral motif through enhanced foraging efficiency.

Do flower mixtures with high functional diversity enhance aphid predators in wildflower strips?

“…Moreover, ladybeetles and hoverfl ies are sensitive to colour, especially yellow (Sutherland et al, 1999;Mondor et al, 2000). Hoverfl ies are also sensitive to fl owers with a contrasting UV-pattern (Koski & Ashman, 2014). Some species with these traits might have been attractive.…”

Evolutionary correlations in flavonoid production across flowers and leaves in the Iochrominae (Solanaceae)

“…Most plant tissues accumulate multiple types of flavonoids, which may serve as pigments, antioxidants, defense compounds, and signaling molecules (Chalker-Scott, 1999;Winkel-Shirley, 1996). For example, many flowers produce anthocyanins (red, blue and purple flavonoid pigments) as well as flavonols, a group of flavonoids that act as co-pigments and create UV-patterning visible to insects (Gronquist et al, 2001;Koski et al, 2014). Moreover, a single type of flavonoid is often found in multiple tissues.…”

Leaf optical properties and dynamics of photosynthetic activity

“…For example, visible radiation reflected from fruits and flowers influences their conspicuousness to pollinators and seed dispersers (Renoult et al 2014), whilst ultraviolet radiation reflectance from the petals affects the conspicuousness of flowers to pollinators (Koski and Ashman 2014). Visible and infrared radiation detected by plants contains information of the surrounding environment and the presence of vegetation (Ballaré and Pierik 2017).…”