title: Diurnal dung beetles use the intensity gradient and the polarization pattern of the sky for orientation.
abstract: To escape competition at the dung pile, a ball-rolling dung beetle forms a piece of dung into a ball and rolls it away. To ensure their efficient escape from the dung pile, beetles rely on a 'celestial compass' to move along a straight path. Here, we analyzed the reliability of different skylight cues for this compass and found that dung beetles rely not only on the sun but also on the skylight polarization pattern. Moreover, we show the first evidence of an insect using the celestial light-intensity gradient for orientation. Using a polarizer, we manipulated skylight so that the polarization pattern appeared to turn by 90 deg. The beetles then changed their bearing close to the expected 90 deg. This behavior was abolished if the sun was visible to the beetle, suggesting that polarized light is hierarchically subordinate to the sun. When the sky was depolarized and the sun was invisible, the beetles could still move along straight paths. Therefore, we analyzed the use of the celestial light-intensity gradient for orientation. Artificial rotation of the intensity pattern by 180 deg caused beetles to orient in the opposite direction. This light-intensity cue was also found to be subordinate to the sun and could play a role in disambiguating the polarization signal, especially at low sun elevations.
authors.affiliation: Department of Biology, Lund University, 223 62 Lund, Sweden basil.el_jundi@biol.lu.se.
authors.forename: Basil
authors.initials: B
authors.lastname: el Jundi
authors.affiliation: Department of Biology, Lund University, 223 62 Lund, Sweden.
authors.forename: Jochen
authors.initials: J
authors.lastname: Smolka
authors.affiliation: Department of Biology, Lund University, 223 62 Lund, Sweden.
authors.forename: Emily
authors.initials: E
authors.lastname: Baird
authors.affiliation: School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits 2050, South Africa.
authors.forename: Marcus J
authors.initials: MJ
authors.lastname: Byrne
authors.affiliation: Department of Biology, Lund University, 223 62 Lund, Sweden School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits 2050, South Africa.
authors.forename: Marie
authors.initials: M
authors.lastname: Dacke
mesh_terms: D000818:Animals; D001517:Coleoptera / Q000502:physiology* / Q000528:radiation effects; D003463:Cues; D008027:Light; D009949:Orientation; D013019:South Africa
keywords: Celestial cues; Compass orientation; Insect; Intensity difference; Polarized light; Scarabaeidae