title: Large variation among photoreceptors as the basis of visual flexibility in the common backswimmer.
abstract: The common backswimmer, Notonecta glauca, uses vision by day and night for functions such as underwater prey animal capture and flight in search of new habitats. Although previous studies have identified some of the physiological mechanisms facilitating such flexibility in the animal's vision, neither the biophysics of Notonecta photoreceptors nor possible cellular adaptations are known. Here, we studied Notonecta photoreceptors using patch-clamp and intracellular recording methods. Photoreceptor size (approximated by capacitance) was positively correlated with absolute sensitivity and acceptance angles. Information rate measurements indicated that large and more sensitive photoreceptors performed better than small ones. Our results suggest that backswimmers are adapted for vision in both dim and well-illuminated environments by having open-rhabdom eyes with large intrinsic variation in absolute sensitivity among photoreceptors, exceeding those found in purely diurnal or nocturnal species. Both electrophysiology and microscopic analysis of retinal structure suggest two retinal subsystems: the largest peripheral photoreceptors provide vision in dim light and the smaller peripheral and central photoreceptors function primarily in sunlight, with light-dependent pigment screening further contributing to adaptation in this system by dynamically recruiting photoreceptors with varying sensitivity into the operational pool.
authors.affiliation: Department of Physics, Biophysics and Biocenter Oulu, University of Oulu, PO Box 3000, Oulun yliopisto 90014, Finland.
authors.forename: Esa-Ville
authors.initials: EV
authors.lastname: Immonen
authors.affiliation: Department of Physics, Biophysics and Biocenter Oulu, University of Oulu, PO Box 3000, Oulun yliopisto 90014, Finland.
authors.forename: Irina
authors.initials: I
authors.lastname: Ignatova
authors.affiliation: Department of Biology, Lund University, Lund, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Gislen
authors.affiliation: Department of Biology, Lund University, Lund, Sweden.
authors.forename: Eric
authors.initials: E
authors.lastname: Warrant
authors.affiliation: Department of Physics, Biophysics and Biocenter Oulu, University of Oulu, PO Box 3000, Oulun yliopisto 90014, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Vähäsöyrinki
authors.affiliation: Department of Physics, Biophysics and Biocenter Oulu, University of Oulu, PO Box 3000, Oulun yliopisto 90014, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Weckström
authors.affiliation: Department of Physics, Biophysics and Biocenter Oulu, University of Oulu, PO Box 3000, Oulun yliopisto 90014, Finland rvfrolov@gmail.com.
authors.forename: Roman
authors.initials: R
authors.lastname: Frolov
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D020062:Heteroptera / Q000502:physiology*; D008027:Light; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D014785:Vision, Ocular
keywords: Notonecta glauca; insect vision; photoreceptor