title: Mayflies are least attracted to vertical polarization: A polarotactic reaction helping to avoid unsuitable habitats.
abstract: Like other aquatic insects, mayflies are positively polarotactic and locate water surfaces by means of the horizontal polarization of water-reflected light. However, may vertically polarized light also have implications for the swarming behaviour of mayflies? To answer this question, we studied in four field experiments the behavioural responses of Ephoron virgo and Caenis robusta mayflies to lamps emitting horizontally and vertically polarized and unpolarized light. In both species, unpolarized light induces positive phototaxis, horizontally polarized light elicits positive photo- and polarotaxis, horizontally polarized light is much more attractive than unpolarized light, and vertically polarized light is the least attractive if the stimulus intensities and spectra are the same. Vertically polarized light was the most attractive for C. robusta if its intensity was about two and five times higher than that of the unpolarized and horizontally polarized stimuli, respectively. We suggest that the mayfly behaviour observed in our experiments may facilitate the stability of swarming above water surfaces. Beside the open water surface reflecting horizontally polarized light, the shadow and mirror image of riparian vegetation at the edge of the water surface reflect weakly and non-horizontally (mainly vertically) polarized light. Due to their positive polarotaxis, flying mayflies remain continuously above the water surface, because they keep away from the unpolarized or non-horizontally polarizing edge regions (water surface and coast line) of water bodies. We also discuss how our findings can explain the regulation of mayfly colonization.
authors.affiliation: Danube Research Institute, MTA Centre for Ecological Research, H-1113 Budapest, Karolina út 29-31, Hungary; Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary. Electronic address: farkas.alexandra@okologia.mta.hu.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Farkas
authors.affiliation: Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary. Electronic address: szaz.denes@gmail.com.
authors.forename: Dénes
authors.initials: D
authors.lastname: Száz
authors.affiliation: Danube Research Institute, MTA Centre for Ecological Research, H-1113 Budapest, Karolina út 29-31, Hungary; Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary. Electronic address: egri.adam@okologia.mta.hu.
authors.forename: Ádám
authors.initials: Á
authors.lastname: Egri
authors.affiliation: Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary; Estrato Research and Development Ltd., H-1124 Budapest, Németvölgyi út 91/c, Hungary. Electronic address: barta@estrato.hu.
authors.forename: András
authors.initials: A
authors.lastname: Barta
authors.affiliation: Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary. Electronic address: polarbeerm@freemail.hu.
authors.forename: Ádám
authors.initials: Á
authors.lastname: Mészáros
authors.affiliation: Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary; Department of Cognitive Neuroscience, Institute of Biology, Eberhard Karls University, Auf der Morgenstelle 28, D-72076 Tübingen, Germany. Electronic address: ramon.hegedus@gmail.com.
authors.forename: Ramón
authors.initials: R
authors.lastname: Hegedüs
authors.affiliation: Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary. Electronic address: gh@arago.elte.hu.
authors.forename: Gábor
authors.initials: G
authors.lastname: Horváth
authors.affiliation: Danube Research Institute, MTA Centre for Ecological Research, H-1113 Budapest, Karolina út 29-31, Hungary; Group for Methodology in Biology Teaching, Biological Institute, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary. Electronic address: kriska@ludens.elte.hu.
authors.forename: György
authors.initials: G
authors.lastname: Kriska
mesh_terms: D000818:Animals; D017753:Ecosystem; D065133:Ephemeroptera / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology; D008027:Light; D014796:Visual Perception / Q000502:physiology*; D014867:Water
chemical_list: D014867:Water
keywords: Caenis robusta; Ephoron virgo; Mayfly; Polarotaxis; Reflection polarization; Water surface