DOI: 10.5061/dryad.wdbrv15kp
title: Data from: A snapping shrimp has the fastest vision of any aquatic animal

description: Animals use their sensory systems to sample information from their
 environments. The physiological properties of sensory systems differ,
 leading animals to perceive their environments in different ways. For
 example, eyes have different temporal sampling rates, with faster-sampling
 eyes able to resolve faster-moving scenes. Eyes can also have different
 dynamic ranges. For every eye, there is a light level below which vision
 is unreliable because of an insufficient signal-to-noise ratio and a light
 level above which the photoreceptors are saturated. Here, we report the
 eyes of the snapping shrimp Alpheus heterochaelis have a temporal sampling
 rate of at least 160 Hz, making them the fastest-sampling eyes ever
 described in an aquatic animal. Fast-sampling eyes help flying animals
 detect objects moving across their retinas at high angular velocities. A.
 heterochaelis are fast-moving animals that live in turbid,
 structurally-complex oyster reefs and their fast-sampling eyes, like those
 of flying animals, may help them detect objects moving rapidly across
 their retinas. We also report the eyes of A. heterochaelis have a broad
 dynamic range that spans conditions from late twilight (~1 lux) to direct
 sunlight (~100,000 lux), a finding consistent with the circatidal activity
 patterns of this shallow-dwelling species.
description: <i>Equipment for electroretinography</i>
 For ERG, we used equipment and methods described previously [7].
 We amplified DC signals using an AM Systems model 3000 AC/DC differential
 amplifier with headstage (Sequim, WA) set to a low-pass cut-off frequency
 of 20 kHz, digitized signals using a ADInstruments PowerLab model 8/35
 data acquisition board (Colorado Springs, CO), and compared signals using
 LabChart 8 Pro (ADInstruments). We dampened electromagnetic and
 vibrational noise by taking recordings inside a custom-built Faraday cage
 that was set atop a passively isolated air table with an attached
 breadboard (ThorLabs SDH7512 and B3048F; Newton, NJ). As electrodes, we
 used electrolytically sharpened 0.2 mm tungsten rods (A-M Systems, Sequim,
 WA). We placed these electrodes using Narishige MM-3 manual
 micromanipulators (Amityville, NY).  
 We used a 150 W tungsten-halogen lamp (Spectral Products
 ASBN-W150-PV; Putnam, CT) to generate light for test stimuli and then
 adjusted the intensity and temporal dynamics of this light using,
 respectively, a continuously variable, circular neutral density filter
 (Edmund Optics 54-082; Barrington, NJ) and a Uniblitz LS3 high speed
 shutter (Rochester, NY). For adapting stimuli, we produced and controlled
 light with a 20 W tungsten-halogen lamp with an integrated shutter (Ocean
 Optics HL-2000-HP-FHSA; Dunedin, FL), along with a continuously variable,
 circular neutral density filter (Edmund Optics 54-082).
   We quantified the absolute irradiance
 (integrated from 375 to 725 nm) of the test stimuli and adapting stimuli
 at a distance and orientation similar to those of the preparations. To do
 so, we used a spectrometer system with components from Ocean Optics that
 included a Flame-S-VIS-NIR-ES spectrometer, a QP400-1-UV-VIS optical
 fiber, and a CC-3 cosine-corrector. To calibrate the absolute response of
 the spectrometer, we used a HL-3P-CAL Vis-NIR calibrated light source. We
 operated the system using Ocean View software.
   <i>Procedures for
 electroretinography</i> To prepare animals for
 ERG, we chilled them in ice cold NSW. Next, to prevent animals from
 desiccating, we wrapped them in a Kimwipe that had been soaked in chilled
 NSW. We then attached animals to a nylon post by wrapping them in
 Parafilm. To perform monopolar recordings, we placed the recording
 electrode into an animal's right eye and placed the reference
 electrode, electrically coupled to ground, into the animal's dorsal
 thorax.   To find an appropriate
 stimulus intensity for assessing the CFF<sub>max </sub>of the
 eyes of <i>A. heterochaelis</i>, we calculated their
 response–stimulus intensity (<i>V</i>log<i>I</i>)
 function. To do so, we used ERG to record the response magnitudes of eyes
 (n = 8) to white light stimuli of varying intensities [17]. In these
 trials, we dark-adapted animals for 15 minutes, then presented a series of
 stimuli in which each stimulus lasted for 1 s and was followed by a 15 s
 dark period. The intensities of these stimuli ranged from 1.97 x
 10<sup>10</sup> (~ 0.01 lux, equivalent to a quarter moon) to
 1.57 x 10<sup>17</sup> photons/cm<sup>2</sup>/s
 (~100,000 lux, equivalent to direct sunlight). To analyze our results, we
 normalized the response magnitudes of eyes, averaged these normalized
 responses, and then fit a curve to the averaged results using the Zettler
 modification of the Naka-Rushton function [19].<b>
 </b>   Next, we used ERG to
 assess the CFF<sub>max</sub> of the eyes of <i>A.
 heterochaelis</i>. Prior to recordings, we light-adapted animals for
 15 minutes under white light with an intensity of 3.65 x
 10<sup>16</sup> photons/cm<sup>2</sup>/s. We
 recorded the responses of eyes to a flickering white light stimulus with
 an intensity of 1.57 x 10<sup>17</sup>
 photons/cm<sup>2</sup>/s [17]. In all trials, we kept the
 adapting light on continuously, presented stimuli in increasing steps of
 10 Hz, and determined the durations of light stimuli and rest periods
 based on the requirements of the ERG system. We ran three sets of trials,
 each with separate groups of animals. In the first set of trials, we
 presented <i>A. heterochaelis</i> (n = 6) with a series of
 light stimuli flickering at rates of 30-100 Hz in which each stimulus
 lasted for 0.75 s and was followed by a 60 s rest period. In our second
 set of trials, we presented animals (n = 6) with a series of light stimuli
 flickering at rates of 60-130 Hz in which each stimulus lasted for 0.5 s
 and was followed by a 60 s rest period. In our third set of trials, we
 presented animals (n = 8) with a series of light stimuli flickering at
 rates of 100-200 Hz in which each stimulus lasted for 0.5 s and was
 followed by a 90 s rest period.  
 <i>Data analysis</i> To assess the
 range of frequencies over which the eyes of <i>A. heterochaelis
 </i>were able to follow flickering light stimuli, we used R to
 implement an approach similar to Bok et al. [18]. We prepared
 electrophysiological recordings for analysis by smoothing them with a
 moving average algorithm and then linearly detrending them. Next, we
 applied a fast Fourier transform (FFT) to get the relative power of the
 FFT of the responses of each eye at each frequency of stimulation. We
 generated power curves for each eye and then normalized and averaged the
 power curves to produce one averaged power curve for each of the three
 sets of trials. To evaluate whether an eye was following a light stimulus
 flickering at a particular frequency, we used a 5% relative power
 threshold. We defined maximum critical flicker fusion frequency
 (CFF<sub>max</sub>) as the highest frequency stimulus for
 which the averaged relative powers of the FFTs of the responses of eyes
 (hereafter “averaged response powers”) remained above the 5% power
 threshold.