DOI: 10.5061/dryad.2rbnzs7x8
title: Sexually dimorphic eye-size in Dragonfishes, a response to a bioluminescent signaling gap

description: Deep-sea fishes must overcome extremely large nearest-neighbor distances
 and darkness to find mates. Sexual dimorphism in the size of luminescent
 structures in many deep-sea taxa, including dragonfishes (family
 Stomiidae), indicates reproductive behaviors may be mediated by visual
 signaling. This presents a paradox: if male photophores are larger,
 females may find males at shorter distances than males find females.
 Solutions to this gap may include females closing this gap or by males
 gathering more photons with a larger eye. We examine the eye size of two
 species of dragonfishes (Malacosteus niger and Phostomias guernei) for
 sexual dimorphism and employ a model of detection distance to evaluate the
 potential for such dimorphism to bridge the detection gap. This model
 incorporates the flux of sexually dimorphic postorbital photophores and
 eye lens size to predict detection distances. In both species, we found a
 significant visual detection gap in which females find males before males
 find females and that male lens size is larger, marking the second known
 case of size dimorphism in the actinopterygian visual system. Our results
 indicate the larger eye affords males a significant improvement in
 detection distance. We conclude that this dimorphic phenotype may have
 evolved to close the detection gap.
description: <strong>Specimen Data</strong>
 Postorbital photophore area, lens size, and standard length (SL)
 data were taken from 42 spec- imens of M. niger (7.6–16.4 cm SL; 25 male,
 16 female; Table S1) and 63 specimens of P. guernei (4.4–14.0 cm SL; 30
 male, 32 female) obtained from Harvard University’s Museum of Comparative
 Zoology. We took images of the head of each specimen with a Nikon D6
 digital camera and measured the area of the postorbital photophore in cm2
 using ImageJ (Schneider et al., 2012). These data are contained in the
 file `eye_PO_data.csv`. <strong>Flux
 Data</strong> 
 The flux (E) of the postorbital photophore of both species is
 unknown, but we presume it varies with photophore size as in other
 deep-sea teleosts. Therefore, we predicted the flux of each individual
 based on data for the postorbital photophore of Aristostomias scintillans,
 a close relative of both species, from Mensinger and Case (1990, J. of
 Exp. Mar. Biol. & Ecol. 144:1–15). The data for this study are in
 `mes.cas.flux.dat.csv`.
description: # Sexually dimorphic eye-size in Dragonfishes, a response to a
 bioluminescent signaling gap Two files are required to run our analysis:
 1. Specimen data that are contained in a single file `eye_PO_data.csv`.
 The columns include the following: -mcz: the Museum of Comparative Zoology
 catalog number. -sex: the sex of the individual. -mass: the mass of the
 individual (in g); not used in the study. NA values indicate this was not
 measured. -sl: standard length (in cm). -jl: jaw length (in cm); not used
 in the study. NA values indicate this was not measured. -eye: orbit diam
 (in mm); not used in the study as the orbit was often damaged. NA values
 indicate this was not measured. -ao: the area of the anterior orbital
 photophore (in mm^2); only recorded for males of the genus Photostomias;
 NA for all others. -po: the area of the posterior orbital photophore (in
 mm^2). -genus: the genus, Photostomias (P. guernei) or Malacosteus (M.
 niger). -diam. lens diameter in cm. -n: a number assigned to each specimen
 for record keeping. 2. Flux data was modeled on the output of
 Aristostomias scintillans reported Mensinger and Case (1990, J. of Exp.
 Mar. Biol. & Ecol. 144:1–15). The data for this study are in
 `mes.case.flux.dat.csv`. The columns include the following: -PO: the area
 of the posterior orbital photophore (in mm^2). -luminescent output of the
 PO: in photons s^-1. All scripts that perform the analysis and produced
 the figures and tables are contained in the markdown
 file`Vu_et_al_Supplement.Rmd` Any inquiries concerning the analysis can be
 made to Dr. Christopher Kenaley (kenaley[at]bc.edu).