• Bee Exclusion in Bird-Pollinated Salvia Flowers: The Role of Flower Color versus Flower Construction
    Petra Wester, Lianka Cairampoma, Sandra Haag, Jürgen Schramme, Christa Neumeyer and Regine Claßen-Bockhoff
    Int. J. Plant Sci. Special Issue - Evolution and Pollination of Salvia 2020.
    Premise of research. In plants, evolutionary shifts from one pollinator guild to another are normally associated with coordinated changes of several floral characters. These might be floral morphology, color, and scent. On the basis of the animals’ different sizes and shapes as well as their visual and olfactory sensitivities or preferences, floral visitors exert different selective pressures on flowers. Floral traits might act as floral filters, attracting pollinators or excluding unwanted flower visitors. We use the genus Salvia, in which several shifts from bee to bird pollination are known, to examine the potential role of floral color versus floral construction as floral filters.
    Methodology. We studied 26 bee-pollinated, 30 bird-pollinated, and 3 intermediate Salvia species. Besides documenting floral morphology and floral guides, we measured floral spectral reflectance and characterized the flowers’ perception by bees.
    Pivotal results. The color loci of half of the bird-pollinated species (red to humans) are in the achromatic center and thus are less conspicuous to bees. All other species (mostly bluish) have significantly greater color contrast and spectral purity and can be recognized by bees and birds. Nectar guides occurred in almost all bee-pollinated species included in the study but in no bird-pollinated species. The results suggest that color might play a role as a floral filter against bees in only half of the bird-pollinated species, while mechanical bee exclusion appears to be important in all
    bird-pollinated species.
    Conclusions. Our data indicate that bees are excluded from bird-pollinated flowers mainly by floral construction. The red color and the absence of nectar guides in bird-pollinated flowers can be interpreted as adaptations for reducing nectar and pollen theft by bees via visual exclusion without losing attractiveness for birds.
  • Spontaneous quantity discrimination of artificial flowers by foraging honeybees
    Scarlett R. Howard, Jürgen Schramme, Jair E. Garcia, Leslie Ng, Aurore Avarguès-Weber, Andrew D. Greentree, Adrian G. Dyer
    Journal of Experimental Biology 2020
    Many animals need to process numerical and quantity information in order to survive. Spontaneous quantity discrimination allows differentiation between two or more quantities without reinforcement or prior training on any numerical task. It is useful for assessing food resources, aggressive interactions, predator avoidance and prey choice. Honeybees have previously demonstrated landmark counting, quantity matching, use of numerical rules, quantity discrimination and arithmetic, but have not been tested for spontaneous quantity discrimination. In bees, spontaneous quantity discrimination could be useful when assessing the quantity of flowers available in a patch and thus maximizing foraging efficiency. In the current study, we assessed the spontaneous quantity discrimination behaviour of honeybees. Bees were trained to associate a single yellow artificial flower with sucrose. Bees were then tested for their ability to discriminate between 13 different quantity comparisons of artificial flowers (numeric ratio range: 0.08–0.8). Bees significantly preferred the higher quantity only in comparisons where ‘1’ was the lower quantity and where there was a sufficient magnitudinal distance between quantities (e.g. 1 versus 12, 1 versus 4, and 1 versus 3 but not 1 versus 2). Our results suggest a possible evolutionary benefit to choosing a foraging patch with a higher quantity of flowers when resources are scarce.
  • Honeybees prefer novel insect-pollinated flower shapes over bird-pollinated flower shapes
    Scarlett R. HOWARD, Mani SHRESTHA, Juergen SCHRAMME, Jair E. GARCIA, Aurore AVARGUE` S-WEBER, Andrew D. GREENTREE, and Adrian G. DYER
    Current Zoology 2019
    Plant–pollinator interactions have a fundamental influence on flower evolution. Flower color signals are frequently tuned to the visual capabilities of important pollinators such as either bees or birds, but far less is known about whether flower shape influences the choices of pollinators. We tested European honeybee (Apis mellifera) preferences using novel achromatic (gray-scale) images of 12 insect-pollinated and 12 bird-pollinated native Australian flowers in Germany; thus, avoiding influences of color, odor, or prior experience. Independent bees were tested with a number of parameterized images specifically designed to assess preferences for size, shape, brightness, or the number of flower-like shapes present in an image. We show that honeybees have a preference for visiting images of insect-pollinated flowers and such a preference is most-likely mediated by holistic information rather than by individual image parameters. Our results indicate angiosperms have evolved flower shapes which influence the choice behavior of important pollinators, and thus suggest spatial achromatic flower properties are an important part of visual signaling for plant–pollinator interactions.
  • Assessing the ecological significance of bee visual detection and colour discrimination on the Evolution of flower colours
    Zoà« Bukovac, Alan Dorin, Valerie Finke, Mani Shrestha, Jair Garcia, Aurore Avarguès-Weber, Martin Burd, Jürgen Schramme, Adrian Dyer
    Evol Ecol 2017
    Bee pollinators interact with flowers in a complex signal-receiver system. Chromatic traits that allow reliable discrimination between rewarding and non-rewarding flowers have been proposed as an important feature of pollination syndromes: bee-pollinated flowers have spectral profiles that closely match the discrimination peaks of their pollinators across the visual spectrum. However, in the complexity of a natural environment, it may be hard for bees to even detect the presence of flowers. In particular, little is known about how discrimination and detection by bees may together contribute to pollinator-mediated selection on floral colour signals. We address here an unexplained Feature of floral colour evolution: the extreme paucity of spectral patterns with pronounced changes in reflectance around 420-480 nm wavelength. We began by conducting experiments with honeybees in a Y-maze to determine their capacity to detect a stimulus rarely found in bee-pollinated flowers - one with a single sharp spectral reflectance change at 478 nm. We found bees to be poor at detecting this stimulus against a neutral background. We then conducted behaviourally-informed computer simulations that test how bee visual discrimination and detection interact, which yielded information about which flower flower colours most effectively facilitate cross-pollination. Finally, we identified from our previous work those bird-pollinated species whose floral colours had spectral characteristics similar to the stimulus used in the Y-maze experiment. These data demonstrate that plants can, and do, produce such spectra for pollinators other than bees. In combination, our results show that the interaction between colour discrimination and detection is important for understanding flower community assembly.
  • Rod-cone based color vision in seals under photopic conditions
    Daniela Oppermann, Jürgen Schramme, Christa Neumeyer
    Vision Research, Volume 125, August 2016, Pages 30-40
    Marine mammals have lost the ability to express S-cone opsin, and possess only one type of M/L-cone in addition to numerous rods. As they are cone monochromats they should be color blind. However, early behavioral experiments with fur seals and sea lions indicated discrimination ability between many shades of grey and blue or green. On the other hand, most recent training experiments with harbor seals under ”mesopic” conditions demonstrated rod based color blindness (Scholtyssek et al., 2015). In our experiments we trained two harbor seals (Phoca vitulina) and two South African fur seals (Arctocephalus pusillus) with surface colors under photopic conditions. The seals had to detect a triangle on grey background shown on one of three test fields while the other two test fields were homogeneously grey. In a first series of experiments we determined brightness detection. We found a luminance contrast of >3% sufficient for correctly choosing the triangle. In the tests for color vision the triangle was blue, green or yellow in grey surround. The results show that the animals could see the colored triangle despite minimal or zero brightness contrast. Thus, seals have color vision based on the contribution of cones and rods even in bright daylight.
  • Training experiments with Bombus terrestris and Apis mellifera on artificial ‘Salvia’ flowers
    Janina Stöbbe, Jürgen Schramme, Regine Claßen-Bockhoff
    Flora - Morphology, Distribution, Functional Ecology of Plants (2015).
    Many bee flowers demand physical force from their pollinators. An example is Salvia with lever-like anthers restricting access to nectar. Though the needed force is generally low, it is largely unknown how far even low forces affect flower preference and foraging behaviour of bees. In the present paper, we introduce a method to measure the response of bees to a force mechanism. We explain the construction of artificial flowers mimicking the lever mechanism of a Salvia flower and the procedure to train honeybees and bumblebees to the models. We document the behaviour of the bees on models without barriers and on those with low forces aiming at the same time to determine the bees’ sensibility for discriminating amongst slightly different flower constructions. Artificial flowers with and without movable levers are constructed to test the effect of a present or absent lever under standardised conditions. Both model types offer sugar syrup (37%) of the same volume. The lever force is 2.8-3.8 mN corresponding to the average force in bee-pollinated Salvia species. Choice experiments, five minutes each, are conducted with single bumblebees (lab, n = 40) and honeybees (outdoors, n = 40). The animal's behaviour and visitation frequency, handling time and flight time between two flower visits are recorded and statistically evaluated. Both bee species can learn to handle the complex artificial flowers. They significantly prefer the model without any barrier indicating that they are able to discriminate amongst models without and with low force demands. The results clearly illustrate that the artificial flowers are suitable for experiments. Continuative choice experiments with reciprocal models of nectar concentration and force will provide a deeper insight into the cost-benefit ratio by bees.
  • Understanding color vision, with comments on mind and matter
    Christoph v. Campenhausen and Jürgen Schramme
    Sensory Perception Mind and Matter. Friedrich G. Barth, Patrizia Giampieri-Deutsch & Hans-Dieter Klein. S. 161-174, Springer 2012
    Much is known about the mental and physical aspects of color vision. Color vision, therefore, is a paradigm well suited for the discussion of the relationship between mind and matter. The aim of the present chapter is to support the proposition that mental affairs cannot be adequately understood if their neurobiological aspects are neglected. Although it is possible to focus on fundamental problems of general relevance when discussing mind and matter, this chapter will deal with specific observations rather than general issues. The possibility of generalisations derived from empirical results is always limited. Provided the conditions under which these observations were made can be confirmed, specific results are reliable. The relationship of mind and matter often comes under the headline 'mind-body' or 'mind-brain-problem' to facilitate the discussion of certain aspects. With regard to perception, a critical early step is the transduction of the stimuli to sensory excitation. Subsequently, the term 'matter' will be subdivided here into 'physics of the stimuli' on the one hand and 'eye and brain', on the other. This will help to clarify, why the transition from the physical aspects of color vision to the mental domain of color is possible, whereas subjective color sensations cannot be traced back to their physical causes.
  • Quantitativer Vergleich des Ostwald’schen Farbsystems mit dem DIN-Farbsystem auf der Basis des Physiologischen Farbsystems (PCS)
    Eine Studie von Marc B. Schuler, Andreas Heinemann und Esther Wetzel unter Anleitung von Dr. Jürgen Schramme. Mitteilungen der Wilhelm-Ostwald-Gesellschaft zu Großbothen e.V., 10.Jg., Heft1, 2005
  • Thames & Kosmos Experiment Kit: Mind’s Eye. Optical Illusions & Human Perception.
    by Christoph v. Campenhausen und Jürgen Schramme 2003

  • Vor- und Nachgeschichte von Wilhelm Ostwalds Farbsystem. Die Entwicklung von ästhetischen Farbsystemen zum physiologischen.
    C. v. Campenhausen & J. Schramme
    Phänomen Farbe, 23. Jahrgang, S. 14-20, September 2003
  • Lightness Constancy: Shades are compensated in perception, scattering light not
    Regine Armann, Christine Seelmann and Jürgen Schramme
    2003 in Norbert Elsner and Herbert Zimmermann, The Neurosciences from Basic Research to Therapy, Proceedings of the 29th Göttingen Neurobiology Conference and the 5th Meeting of the German Neuroscience Society 2003; p. 1017
  • Some properties of the physiological colour system
    C. von Campenhausen and J. Schramme
    Normal and Defective Colour Vision. J. D. Mollon, J. Pokorny & K. Knoblauch. S. 289-295, 2003

  • The influence of colour on the scintillating grid illusion
    Schrauf M, Schramme J,
    Perception 31 ECVP Abstract Supplement 2002

  • Colored shadows - a quantitative analysis
    Kallmann, AJ; Schramme, J; Neumeyer, C
    INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE Volume: 43 Supplement: 2 Pages: U1045-U1045 MAY 2002
  • The influence of colored backgrounds and colored lines on the Scintillating Grid Illusion
    Schrauf, M.; Weihe, T.; Müller, T.; Schramme, J.; Campenhausen, C. v.
    in Zoology (105) Supplement V, 95. Annual Meeting of the Deutsche Zoologische Gesellschaft Halle(Saale), May 20-24, 2002. Urban & Fischer, p. 46
  • Das Phänomen der farbigen Schatten - ein Spezialfall der Farbkonstanz?
    Anatol Julian Kallmann, Jürgen Schramme & Christa Neumeyer
    5. Tübinger Wahrnehmungskonferenz 22. - 24. Februar 2002
  • The physiological color system.
    J. Schramme & C. v. Campenhausen
    2001 in Elsner N & Kreutzberg W, Göttingen Neurobiology Report 2001, Proceedings of the 4th meeting of the German Neuroscience Society 2001; Volume II. p. 1029
  • Three-dimensional interpretation of the color system of Aguilonius/Rubens 1613.
    C. v. Campenhausen, C. Pfaff und J. Schramme
    COLOR research and application, Supplement Volume 26. 2001
  • 'Coloured shadows': why are they so vivid?
    Neumeyer C, Kallmann J, Schramme J,
    Perception 29 ECVP Abstract Supplement 2000
  • Farbkonstanz und ein einfacher Trick zu ihrer Demonstration.
    C. v. Campenhausen und J. Schramme
    Praxis der Naturwissenschaften - Physik. 3/49 S. 2-6. 2000
  • Psychophysik des Farbensehens.
    C. v. Campenhausen
    Deutsche Physikalische Gesellschaft, Frühjahrstagung des Fachverbandes Didaktik der Physik, Ludwigsburg 1999, S.119-134.
    C. v. Campenhausen & J. Schramme
    Erweiterte Fassung auf der Tagungs-CD der obengenannten Tagung.
  • Anleitungen zu Experimenten über das Farbensehen.
    C. v. Campenhausen und J. Schramme
    Praxis der Naturwissenschaften - Physik. 5/47 S. 14-15. 1998
  • Psychophysik des Farbensehens.
    C. v. Campenhausen und J. Schramme
    Praxis der Naturwissenschaften - Physik. 5/47 S. 4-13. 1998
  • Duftfamilien auf der Landkarte der Parfüms Ein neuartiger Ansatz zur Klassifikation von Düften
    J. Schramme
    Parfümerie und Kosmetik, 7/8 Juli/August 1998, S.34-37.
  • Psychophysical investigation of lateral coupling in the retina due to pattern-induced flicker colors (PIFCs)
    C. Sonntag & J. Schramme
    1998 in Zissler D, Zoology (101) Supplement I, Analysis of Complex Systems, Proceedings of the 91. Annual Meeting Leipzig, 1.-4. June 1998. Gustav Fischer, p. 53
  • Andenken Zoologischer Vergangenheit
    Katalog zur Ausstellung im Naturhostorischen Museum Mainz vom 20. Mai bis 06. Juli 1997. Hrsg. v. Campenhausen, C. mit Kleinmann, J., Schmidt, U. & Schramme, J.; Mainz, 1997
  • Musterinduzierte Flimmerfarben werden im Großhirn verändert
    N. Supply & J. Schramme
    1997 in Zissler D, Verhandlungen der Deutschen Zoologischen Gesellschaft, 90. Jahresversammlung 1997 in Mainz (Stuttgart: Gustav Fischer) 393
  • Cortical modification of pattern induced flicker colors
    J. Schramme and N. Supply
    Investigative Ophthalmology & Visual Science, Annual Meeting Abstract Book - Part II, March 15, 1997, Vol. 38, No. 4, p. S900
  • 100 years of Benham’s top in colour science.
    Christoph von Campenhausen, Jürgen Schramme
    Perception, 1995, volume 24, pages 695-717
    For 100 years Benham's top has been a popular device demonstrating pattern induced flicker colours (PIFCs). Results of early and recent investigations on PIFCs are reported showing that the phenomenon originates in phase sensitive lateral interactions of modulated neural activity in the retina followed by additional spatial interactions in the visual cortex behind the locus of binocular fusion. Colour matches with normal colour stimuli indicate that S/(M+L) opponent neurons are involved. Dichromats do not find matching stimuli for all PIFCs. PIFCs may become useful in medical diagnosis. The phenomenon is interpreted as a side effect of a neural mechanism providing colour constancy under normal stimulus conditions.
  • Color constancy under real-world light conditions
    J. Schramme and A. Quäschning
    Investigative Ophthalmology & Visual Science, Annual Meeting Abstract Issue, March 15, 1995, Vol. 36, No. 4, p. S470
  • The blue-yellow opponent channel of the human retina mediates pattern induced flicker colors and color constancy
    J. Schramme
    Investigative Ophthalmology & Visual Science, Annual Meeting Abstract Issue, March 15, 1993, Vol. 34, No. 4, p. 747
  • Changes in pattern induced flicker colors are mediated by the blue-yellow opponent process.
    Vision-Res. 1992 Nov; 32(11): 2129-34
    The colors of Benham's Top [pattern induced flicker colors (PIFCs)] were matched with color stimuli provided by a computer aided color mixer. Subjects viewed a series of specifically modified black and white disks and matched the resulting subjective color with a comparison field containing the color generated by additive mixing. Different phase relations between the apparently colored ring and the surround were tested. The color loci of all PIFCs were found to lie on a plane in receptor three-space which is given by the axis of the shortwave receptor excitation and a vector given by combining the middle and long wave receptor excitation directions in a fixed ratio of nearly 1:1. From the orientation of this plane it can be deduced that the blue-yellow opponent process (the blue-on-center cells) alone accounts for the different PIFCs.
  • Color induction via non-opponent lateral interactions in the human retina.
    von-Campenhausen-C; Hofstetter-K; Schramme-J; Tritsch-MF
    Vision-Res. 1992 May; 32(5): 913-23
    Retinal connections causing colors in Benham's top (pattern induced flicker colors, PIFCs) are investigated by psychophysical experiments. PIFCs are still seen when stimuli to different cones are demodulated selectively, indicating the involvement of non-opponent channels. PIFCs also occur on retinal areas next to those affected by modulated stimuli; further, both monochromat and dark-adapted trichromats perceive PIFCs which are achromatic. These additional findings point to horizontal cells as neuronal mediators of modulated excitation leading to PIFCs. The unspecifity of the postulated connection with respect to cone types agrees with anatomic findings of Boycott, B. B., Hopkins, J. M. and Sperling, H. G. (1987, Proceedings of the Royal Society of London, B, 229, 345-379) on horizontal cells.
  • Variation des Tageslichts und musterinduzierte Flimmerfarben.
    J. Schramme
    1991 in Pfannenstiel H-D, Verhandlungen der Deutschen Zoologischen Gesellschaft, 84. Jahresversammlung 1991 in Tübingen (Stuttgart: Gustav Fischer) 460
  • Colorimetric Measurement of Pattern Induced Flicker Colors (PIFCs)
    Jürgen Schramme
    1990 in Elsner N, Roth G, Brain - Perception Cognition (Stuttgart: Thieme) 266
  • Farbmetrische Untersuchungen und spektrale Empfindlichkeitsmessungen zu Musterinduzierten Flimmerfarben.
    Jürgen Schramme, Mark F. Tritsch
    1988 in Elsner N, Barth F G, Sense Organs (Stuttgart: Thieme) 282
  • Messanordnung zur farbmetrischen Bestimmung von musterinduzierten Flimmerfarben
    Jürgen Schramme
    1984 im Tagungsband zur Neurobiologen-Tagung: Vergleichende Neurobiologie des Verhaltens, S. 241