Council, UK.rstb.royalsocietypublishing.org Phil. Trans. R. Soc. B 369:

Over
Council, UK.rstb.royalsocietypublishing.org Phil. Trans. R. Soc. B 369:
Over the past five decades, considerable effort has been devoted to understanding the strategies and visual cues that honeybees use to navigate to food sources, and to uncovering the underlying mechanisms. We now know that bees are not only capable of estimating the distance and the direction of an attractive food source, but also of communicating this information to their nest-mates, purchase PD168393 through the famous `waggle dance’ [1]. In the waggle dance, which is performed on the vertical surface of a honeycomb, bees indicate the azimuthal direction of the food source relative to the azimuth of the sun as the angle between the vertical and the direction of the axis of the waggle. The sun is used as a reference in the bee’s internal compass. Thus, a dance with a waggle axis oriented 308 clockwise with respect to the vertical implies that the food source is positioned along a direction that is oriented 308 clockwise with respect to the sun’s azimuth. As the day advances, the sun changes its azimuthal position in the sky. Consequently, when a bee flies regularly to and from a given food source through the day, the direction of the waggle axis changes systematically as the sun marches across the sky. When the sun is obscured by a cloud, it is believed that bees are stillElectronic supplementary material is available at http://dx.doi.org/10.1098/rstb.2013.0037 or via http://rstb.royalsocietypublishing.org.2014 The Author(s) Published by the Royal Society. All rights reserved.able to obtain a compass reference from the unoccluded part of the sky, by making use of the pattern of polarization that the sun creates in the sky [2,3]. Rayleigh scattering of sunlight by the Earth’s atmosphere causes the sun to produce a characteristic pattern of polarization in the sky [3], as shown in figures 2 and 3. If the sun is imagined to be at the pole of the celestial sphere, the e-vectors of the polarized-light pattern in the sky are oriented parallel to the lines of latitude of the sphere, and the degree of polarization of the light is strongest at the equator. Thus, when the sun is near the horizon but obscured by a patch of cloud, the degree of polarization in the sky will be strongest at the zenith, and, if that part of the sky is visible, then a bee can make use of the direction of the e-vector in that region to infer its direction of flight. Flight in a direction perpendicular to the e-vector must mean that the bee is heading directly towards the sun, or directly away from it. On the other hand, flight in a direction parallel to the e-vector must mean that the sun is directly to the left or to the right of the bee, i.e. that the bee is flying at an azimuthal direction that is oriented 908 away, either clockwise or counterclockwise, from the direction of the sun. There is considerable evidence that bees have the capacity to sense the direction of the e-vectors in the celestial polarization pattern [1,4?]. The photoreceptors in the dorsal rim area of the honeybee’s compound eyes PD168393 web exhibit a strong sensitivity to polarized light [10,11]. Moreover, polarization-sensitive interneurons have been found in the medulla [12], suggesting that the polarization pattern in the sky may indeed be analysed by the brain. However, these observations do not, on their own, demonstrate that bees perceive the polarization pattern of the sky and use it to measure or set their flight course. The requisite proof must co.Over
Council, UK.rstb.royalsocietypublishing.org Phil. Trans. R. Soc. B 369:
Over the past five decades, considerable effort has been devoted to understanding the strategies and visual cues that honeybees use to navigate to food sources, and to uncovering the underlying mechanisms. We now know that bees are not only capable of estimating the distance and the direction of an attractive food source, but also of communicating this information to their nest-mates, through the famous `waggle dance’ [1]. In the waggle dance, which is performed on the vertical surface of a honeycomb, bees indicate the azimuthal direction of the food source relative to the azimuth of the sun as the angle between the vertical and the direction of the axis of the waggle. The sun is used as a reference in the bee’s internal compass. Thus, a dance with a waggle axis oriented 308 clockwise with respect to the vertical implies that the food source is positioned along a direction that is oriented 308 clockwise with respect to the sun’s azimuth. As the day advances, the sun changes its azimuthal position in the sky. Consequently, when a bee flies regularly to and from a given food source through the day, the direction of the waggle axis changes systematically as the sun marches across the sky. When the sun is obscured by a cloud, it is believed that bees are stillElectronic supplementary material is available at http://dx.doi.org/10.1098/rstb.2013.0037 or via http://rstb.royalsocietypublishing.org.2014 The Author(s) Published by the Royal Society. All rights reserved.able to obtain a compass reference from the unoccluded part of the sky, by making use of the pattern of polarization that the sun creates in the sky [2,3]. Rayleigh scattering of sunlight by the Earth’s atmosphere causes the sun to produce a characteristic pattern of polarization in the sky [3], as shown in figures 2 and 3. If the sun is imagined to be at the pole of the celestial sphere, the e-vectors of the polarized-light pattern in the sky are oriented parallel to the lines of latitude of the sphere, and the degree of polarization of the light is strongest at the equator. Thus, when the sun is near the horizon but obscured by a patch of cloud, the degree of polarization in the sky will be strongest at the zenith, and, if that part of the sky is visible, then a bee can make use of the direction of the e-vector in that region to infer its direction of flight. Flight in a direction perpendicular to the e-vector must mean that the bee is heading directly towards the sun, or directly away from it. On the other hand, flight in a direction parallel to the e-vector must mean that the sun is directly to the left or to the right of the bee, i.e. that the bee is flying at an azimuthal direction that is oriented 908 away, either clockwise or counterclockwise, from the direction of the sun. There is considerable evidence that bees have the capacity to sense the direction of the e-vectors in the celestial polarization pattern [1,4?]. The photoreceptors in the dorsal rim area of the honeybee’s compound eyes exhibit a strong sensitivity to polarized light [10,11]. Moreover, polarization-sensitive interneurons have been found in the medulla [12], suggesting that the polarization pattern in the sky may indeed be analysed by the brain. However, these observations do not, on their own, demonstrate that bees perceive the polarization pattern of the sky and use it to measure or set their flight course. The requisite proof must co.