DOI: 10.5061/dryad.37pvmcvr9
title: Sexual dichromatism in the fur of a bat: An exploration of color differences and potential signaling functions

description: Sex differences in body color (i.e., sexual dichromatism) are rare in bats
 and, more broadly, in mammals. The eastern red bat (Lasiurus borealis) is
 a common tree-roosting bat that occupies much of North America and has
 long been described as sexually dichromatic. However, previous research on
 this species found that absolute body size and collection year were better
 predictors of fur color in preserved specimens than sex. We revisited this
 issue and photographed 82 live eastern red bats under standardized
 conditions, then used image analysis to quantify pelage hue, saturation,
 and value. We used an information theoretic approach to evaluate four
 competing hypotheses about the principal drivers of color differences in
 the fur of eastern red bats. Our analyses demonstrated that sex was a
 better predictor of pelage color than body size; males had redder, more
 saturated, and lighter pelages than females. Additionally, fur color of
 juvenile vs. adult bats differed somewhat as juveniles were darker than
 adults. In general, absolute body size (i.e., forearm length in bats) was
 a poor predictor of color in live eastern red bats. In an exploratory
 post-hoc analysis, we confirm that fur color is related to body condition
 (i.e., mass in bats), suggesting color might serve as a sexually-selected
 signal of mate quality in this partially-diurnal species. Future work
 should investigate the functional role of sexual dichromatism in this
 species, which could be related to signaling or possibly
 thermoregulation. 
description: Bat Capture We
 followed the guidelines of the American Society of Mammalogists for the
 use of wild mammals in research (Sikes et al. 2019), institutional animal
 care and use protocols (University of Illinois Urbana-Champaign, #21022),
 and all white-nose syndrome decontamination recommendations (White-nose
 Syndrome Disease Management Working Group 2020). We held appropriate
 Indiana and USFWS permits. Photography
 We performed all photography in the
 field. We held each bat in a standardized position (wings closed, forearms
 held against body and uropatagium spread, with bats’ ventral surface down)
 and photographed them in a portable LED-lit photo studio box (EMART
 International Inc., Westminster, CA, USA) using a digital single-lens
 reflex camera (EOS Rebel T6) with an EFS 18-55 mm lens (Canon, Tokyo,
 Japan). To achieve homogeneous lighting conditions, we did not use flash
 to photograph bats but relied only on the illumination produced by the two
 LED strips within the photo studio box. We photographed the bats from a
 standardized distance (35.56 cm) with camera settings at IOS 800, a
 shutter speed of 1/800th of a second, and f/5.6 (10.9 mm). We photographed
 bats against a neutral gray background and included a color correction
 card within each photograph. We photographed and stored all images in
 large format.  Color Analyses We performed all color analyses in ImageJ
 version 1.8.0 (Schneider et al. 2012; Rasband 2018). For this study, we
 used hue, saturation, and value scores to describe fur color. Hue
 describes colors in their purest forms (e.g., red, blue, etc.). Hue scores
 range from 0–359°, with shades of red, orange, and yellow occurring from
 0–30°. Saturation describes the purity or intensity of any color,
 expressed as a percent. Lower saturation scores indicate less vibrant
 colors. Value describes how close a color is to white or black (i.e.,
 brightness) and is also expressed as a percent. Lower value scores
 indicate darker colors. To quantify the color of bat fur, we selected the
 furred dorsal surface of each bat’s exposed uropatagium (the membrane that
 extends between the hind limbs) to measure (hereafter, “selected area”).
 For each bat, we quantified the average hue, saturation, and value scores
 across the selected area. We also quantified color across the whole of
 each bat’s exposed dorsal surface. Ultimately, the color scores of the two
 surface types were highly correlated (Pearson’s correlation coefficients
 &gt;0.90; data not shown), and we opted to use the uropatagium scores
 to facilitate comparisons with earlier work by Davis and Castleberry
 (2010). To assess whether variation in the size of the selected area
 influenced our analysis, we quantified the number of pixels within each
 selected area. Ultimately, the selected area size was not related to hue,
 saturation, or value scores (linear models, F<sub>1,78</sub> = 0.80, 0.04, and 0.19; <em>p</em> = 0.373, 0.838, and 0.661, respectively), and we did not include it as a covariate in our models. Overall, these scoring techniques produced reliable measurements that could be consistently replicated (for details on reliability analyses, see Appendix S1, Supplementary Text).
description: # Sexual dichromatism in the fur of a bat: An exploration of color
 differences and potential signaling functions --- Data that support the
 results outlined in our manuscript, titled "Sexual dichromatism in
 the fur of a bat: An exploration of color differences and potential
 signaling functions." For information on how the data were collected,
 please refer to the manuscript. ## Description of the Data and file
 structure Dataset is stored in csv format and contains the following
 headers: image_id: unique id associated with each representative image
 age: age of bat, adult or juvenile sex: sex of bat, female or male repro:
 reproductive condition of bat, pregnant, lactating, post-lactating,
 nonreproductive, or scrotal mass: mass of bat (xx.x) in grams fal: forearm
 length of bat (xx.x) in mm area_uro: pixels housed within the selected
 area of the uropatagium hue_uro: mean hue score across selected area of
 the uropatagium saturation_uro: mean saturation score across selected area
 of the uropatagium value_uro: mean value score across selected area of the
 uropatagium hue_bod: mean hue score across selected area of exposed dorsal
 surface saturation_bod: mean saturation score across selected area of
 exposed dorsal surface value_bod: mean value score across selected area of
 exposed dorsal surface gray_mean_bright: mean brightness, scored across
 gray square in color standard card mean_red: mean red score across
 selected area of the uropatagium mean_green: mean green score across
 selected area of the uropatagium mean_blue: mean blue score across
 selected area of the uropatagium ## Sharing/access Information Data will
 be made publicly available upon acceptance.