Endogenous and exogenous change in krill visual sensitivity and speed with midday twilight.

• Main Authors: Jonathan H. Cohen (7958483), Kim S. Last (11581392), Corie L. Charpentier (3200505), Finlo Cottier (749186), Malin Daase (471602), Laura Hobbs (9152223), Geir Johnsen (257802), Jørgen Berge (235355)
• Format: Still Image
• Language: unknown
• Published: 2021
• Subjects: Physiology; Ecology; Inorganic Chemistry; Environmental Sciences not elsewhere classified; Astronomical and Space Sciences not elsewhere classified; Biological Sciences not elsewhere classified; thysanoessa inermis </; therefore question whether; main migratory species; acoustic field observations; 81 ° n; 5 ° n; arctic ocean extends; light measurements demonstrate; characterize light across; weak midday twilight; div >< p; arctic krill (<; arctic polar night; arctic krill; light plays; polar night; zooplankton community; using electroretinogram; traditional definitions; sun ’; subjective night; photophysiological cycles; north pole; midnight sun; maximum extent; lower latitudes; latitudinal gradient; high latitudes; fundamental role; darkest parts; constant darkness; circadian clock; auroral components; although differences; Arctic; Arctic Ocean; North Pole; Arctic krill; Zooplankton; Thysanoessa inermis
• Online Access: https://doi.org/10.1371/journal.pbio.3001413.g003

(a) Response irradiance (V-log I ) curves for T . inermis , with experiments testing endogenous (circles, subjective) and exogenous (squares, acclimation) sensitivity change at 1°C. Endogenous experiments were conducted during subjective night (black circles, n = 8) and day (gray circles, n = 8). Exogenous experiments were conducted during the day with krill ( n = 6) tested first under dark acclimation (black squares) and then under simulated midday twilight acclimation (gray squares). Symbols represent means (± 1 SD) of V-log I models fit to normalized ERG data, with aggregate data fit by a V-log I model (solid lines). (b) Log irradiance at half-saturation for V-log I models (Log K) of each individual krill, with symbols as described for (a). Light acclimation experiments were paired Dark-Light, so points corresponding to the same individual are connected by a dashed line. Log K was lower during both subjective night ( p = 0.038, rank sum test) and dark acclimation ( p = 0.031, signed rank test) when compared to corresponding subjective day and light acclimation treatments in each experiment, respectively. (c) Speed of vision as determined by response latency (elapsed time between onset of the light flash and onset of the photoreceptor response at 50% V max ). Response latency was analyzed for all individuals plotted in (b) and plotted with the same symbol designation. Response latency did not differ between subjective night and day ( p = 0.833, rank sum test), but decreased with light acclimation ( p = 0.031, signed rank test). For data, see S2 Data .