Pollen Signals

Pollen is the vector in the sexual reproduction of flowering plants as well as a floral reward for pollen eating insects like syrphid flies and pollen collecting insects like bees. Since the flowers of primitive angiosperms had no conspicuous signalling apparatus like a corolla, the yellow pollen probably was the first advertising signal of early insect-pollinated flowers. The yellow colour of pollen was caused by flavonoid pigments shielding the pollen against ultraviolet radiation. The flowers of many extant flowering plants visually still display yellow UV-absorbing pollen and anthers. Many other flowers hide the anthers in the floral tube and display anther-mimicking floral guides. The flowering plants that visually display anthers and pollen, those that mimic stamens and pollen eating and the pollen collecting flower-visitors probably constitute the most speciose mimicry system in the world. Our research focuses on innate responses of syrphid flies and bees to visual signals of anthers and pollen. Moreover we study which visual, tactile and chemical pollen signals trigger pollen collection in bumblebees.

• Lunau K, Piorek V, Krohn O, Pacini E (2014) Just spines—mechanical defense of malvaceous pollen against collection by corbiculate bees. Apidologie (in press).
• Konzmann S, Lunau K (2014) Divergent rules for pollen and nectar foraging bumblebees - A laboratory study with artificial flowers offering diluted nectar substitute and pollen surrogate. PLoS ONE 9(3): e91900.
• Burkart A, Schlindwein C, Lunau K (2012): Comparative bioacoustical studies on flight and buzzing of neotropical bees. Journal of Pollination Ecology 6: 118-124.
• Lunau K, Unseld K, Wolter F (2009): Visual detection of diminutive floral guides in the bumblebee Bombus terrestris and in the honeybee Apis mellifera. J. Comp. Physiol. A 195: 1121-1130.
• Pohl M, Watolla T, Lunau K (2008): Anther-mimicking floral guides exploit a conflict between innate preference and learning in bumblebees (Bombus terrestris). Behav. Ecol. Sociobiol. 63: 295-302.
• Lunau K (2006): Stamens and mimic stamens as components of floral colour patterns. Bot. Jahrb. Syst. 127: 13-41.
• Dinkel T, Lunau K (2001): How drone flies (Eristalis tenax L, Syrphidae, Diptera) use floral guides to locate food sources. J. Insect Physiol. 47: 1111-1118.

Visual Orientation of Flower-Visitors

The visual signalling apparatus of flowers is considered as an attractant of potential pollinators. Flower-visitors may possess innate preferences for visual properties of flowers such as shape, symmetry, hue of floral colour, colour purity, and colour contrast. However, the visual capabilities among flower-visitors differ, particularly the sensitivity towards ultraviolet and red light. Moreover bees respond to different cues dependant of the distance towards flowers, i.e. green contrast, colour, visual components of the floral colour pattern, i.e. the approach from some distance, the targeting towards a landing site, the landing reaction and the movements on the flower may be triggered by different colour parameters. Our study focuses on the innate colour preferences of flower-visitors and on the sensory exclusion of bees by hummingbird-pollinated flowers.

• Papiorek S, Rohde K, Lunau K (2013) Bees` subtle colour preferences: How bees respond to small changes in pigment concentration. Naturwissenschaften 100: 633-643.
• Rohde K, Papiorek S, Lunau K (2013) Bumblebees (Bombus terrestris) and honeybees (Apis mellifera) prefer similar colours of higher spectral purity over trained colours. J. Comp. Physiol. A 199: 197-210.
• Lunau K, Papiorek S, Eltz T, Sazima M (2011): Avoidance of achromatic flower colours by bees opens private channel for hummingbirds. J. Exp. Biol. 214: 1607-1612.
• Heuschen B, Gumbert A, Lunau K (2005): A generalised mimicry system involving angiosperm flower colour, pollen and bumblebees' innate colour preferences. Plant Syst. Evol. 252: 121-137.
• Lunau K, Wacht S, Chittka L (1996): Colour choices of naive bumble bees and their implications for colour perception. J. Comp. Physiol. A 178: 477-489.

Coloured cornea lenses in dipterans

Some dipterans display coloured corneal lenses in their compound eyes. The multi-layer corneal lenses reflect a large portion of incident light in a distinct waveband due to reflective interference. This phenomenon is known in species of Tabanidae, Dolichopodidae, Tephritidae, Sciomycidae and other dipteran families. The phenomenon is not yet understood. Our research focuses on the analysis of the light habitat of flies with coloured corneal lenses and the courtship behaviour in which the males display tiny black-and-white signals.

• Lunau K, Knüttel H (1995): Vision through coloured eyes. Naturwissenschaften 82: 432-434.

Eye Mimicry

The imitations of eyes, the so-called eyespots or ocelli, are known from different taxa like butterflies, fish and birds. A specific feature of many eye spots is the imitaion of an area of total light reflection - the sparkle. It is not known whether the similarity of ocelli to natural vertebrate eyes or the conspicuousness of the colour pattern causes the deterrent effect. Our studies focus on the testing of the eye-mimicry hypothesis and conspicuousness hypothesis in lepidopteran ocelli by testing eye-spot which are equally conspicuous but differ in their similarity to natural eyes. In another project we study the function of eyespots in male peacock pheasants and argus pheasants and test the hypothesis that the ocelli of these species mimic food items - seeds or fruits.

• Blut C, Wilbrandt J, Fels D, Girgel EI, Lunau K (2012): The ‘sparkle’ in fake eyes – the protective effect of mimic eyespots in Lepidoptera. Entomologia experimentalis et applicata 143: 231–244.
• Lunau K (2011): Warnen, Tarnen, Täuschen. Mimikry und Nachahmung bei Pflanze, Tier und Mensch. Wissenschaftliche Buchgesellschaft, Darmstadt; 160pp.