DOI: 10.5061/dryad.prr4xgxtd
title: Data from: Functional differences between the extraordinary eyes of deep-sea hyperiid amphipods

description: The ocean’s midwater is a uniquely challenging yet predictable and simple
 visual environment. The need to see without being seen in this dim, open
 habitat, has led to extraordinary visual adaptations. To understand these
 adaptations, we compared the morphological and functional differences
 between the eyes of three hyperiid amphipods – Hyperia galba, Streetsia
 challengeri, and Phronima sedentaria. Combining micro-CT data with
 computational modelling, we mapped visual field topography and predicted
 detection distances for visual targets viewed in different directions
 across mesopelagic depths. Hyperia’s eyes provide a wide visual field
 optimized for spatial vision over short distances, while Phronima and
 Streetsia’s eyes have the potential to achieve greater sensitivity and
 longer detection distances using spatial summation. These improvements
 come at the cost of smaller visual fields, but this loss is compensated
 for by a second pair of eyes in Phronima and with behaviour in Streetsia.
 The need to improve sensitivity while minimizing visible eye size to
 maintain crypsis has likely driven the evolution of hyperiid eye
 diversity. Our results provide an integrative look at how these elusive
 animals have adapted to the unique visual challenges of the mesopelagic.
description: Specimens were euthanized by being immersed in iced seawater or
 the addition of a few drops of 95% ethanol to their holding tank. The
 heads and anterior-most segments of <em>Hyperia</em> and
 <em>Phronima</em> were dissected from the body, then fixed in
 4% seawater buffered formalin (<em>Hyperia</em>) or 2%
 cacodylate buffered glutaraldehyde (<em>Phronima</em>).
 <em>Hyperia</em> and <em>Phronima</em> specimens
 were run through a dehydration series then stained with a 0.5%
 phosphotungstic acid (PTA) solution in 70% ethanol for 30 days before
 scanning. <em>Streetsia</em> specimens were fixed in 4%
 phosphate buffered paraformaldehyde and stained with an aqueous 1% w/v
 iodine and 2% w/v potassium iodide solution for seven days. Specimens were
 mounted in 500 µl sealed Eppendorf tubes stabilized with either minute
 blocks of foam or 1% low temperature gelling agarose.
 <em>Hyperia</em> and <em>Phronima</em> specimens
 were scanned using a GE Phoenix v|tome|x M 240/180 kV Dual Tube micro-CT
 at the Smithsonian National Museum of Natural History at 80 – 90 kV and
 2.65 – 4.26 W, with optical magnification of 70.8 and 36.6x.
 S<em>treetsia</em> specimens were scanned with a Versa 520 XRM
 (Zeiss, Pleasanton, CA, USA) at 70 kV and 6 W with 4x optical
 magnification at the University of Western Australia. Voxel sizes of 2.82
 – 11.17 µm were achieved and the standard 0.7 kernel size reconstruction
 filter was used. Raw projection data from <em>Hyperia</em> and
 <em>Phronima</em> were reconstructed using datos|X (GE Sensing
 and Inspection Technologies GmbH) and visualized and exported using VG
 Studio (Volume Graphics), while XRM Reconstructor software
 (v.10.7.3679.13921, Zeiss) following a standard centre shift and beam
 hardening (0.1) correction was used for
 <em>Streetsia</em>.
description: # Functional differences between the extraordinary eyes of deep-sea
 hyperiid amphipods
 [https://doi.org/10.5061/dryad.prr4xgxtd](https://doi.org/10.5061/dryad.prr4xgxtd) * The .nii files included in this data set were acquired using X-ray tomography. Each file contains a stack of greyscale images that can be imported into 3D image visualization software. X-ray tomography was conducted on two specimens of three iodine-stained hyperiid amphipods. * The MATLAB files included in this dataset contain the data extracted from the .nii files using our custom-made MATLAB software which has also been uploaded here. These data were also used in our optical models conducted using MATLAB scripts that have also been uploaded here.