DOI: 10.5061/dryad.6wwpzgn9j
title: Behavioural choice and background matching facilitate camouflage in the European garden spider

description: Visual camouflage via background matching involves a variety of adaptive
 traits to maintain crypsis, including intraspecific color variation,
 behavioral choice of substrates, and color change. These non-mutually
 exclusive solutions frequently act together to conceal and deceive prey
 and enemies. Here, we combine field observations, image analysis, and
 laboratory experiments to investigate which processes drive camouflage in
 the garden cross spider (Araneus diadematus), a species with body
 coloration that varies in shades of brown. We demonstrate that A.
 diadematus does not change color significantly, at least within the same
 instar, when retained on substrates of different coloration. However,
 there is strong behavioral selection through active substrate choice
 across spiders for color-matching substrates (dead brown leaves over green
 leaves) when offered a choice under laboratory conditions. Similar
 background selection also apparently occurs in nature, where spiders were
 often observed on brown leaves, even though they are less common than
 green ones. In general, vision modeling shows that there is a high overlap
 in the diversity of brown shades (from pale to dark) between spider bodies
 and dead leaves available in the environment. Image analyses also revealed
 that spiders fine-tune their camouflage on an individual level by matching
 the tones (from pale to dark) of their host leaves. Therefore, we
 demonstrate how behavior coupled with variation in color phenotypes
 facilitates camouflage at different scales.
description: We collected garden cross spiders (<em>Araneus
 diadematus</em>) and plant leaves (green and brown from host plants;
 brown from sympatric species) in the field for use in laboratory
 experiments. In the field study and colour change experiment, we
 quantified spider colour and camouflage from digital photographs using
 methods of image analysis and visual modelling. In the behavioural-choice
 experiment, we recorded spider preferences between green and brown leaves
 in binomial trials.
description: # Behavioural choice and background matching facilitate camouflage in the
 European garden spider https://doi.org/10.5061/dryad.6wwpzgn9j Authors:
 Yuri Fanchini Messas; Rafael Campos Duarte; João Vasconcellos-Neto; and
 Martin Stevens Contact: Yuri Fanchini Messas,
 [yurimessas@gmail.com](mailto:yurimessas@gmail.com) ## Abstract Here, we
 used image analysis and visual modelling of an avian predator (the
 Eurasian Blue Tit *Cyanistes caeruleus*) to assess the color variation and
 camouflage of European garden spiders (*Araneus diadematus*) inhabiting
 shrub vegetation in southwest UK. We predicted that spiders would be more
 effectively camouflaged on their chosen resting substrates (brown host
 leaves) compared to other substrates available in the surrounding
 environment. Additionally, we hypothesize that *A. diadematus* background
 matching relies on phenotypic plasticity in spiders’ body coloration, with
 a fine-scale individual resemblance to the color of the host leaf, or of
 behavioral selection of backgrounds resembling an individual’s own
 appearance. Herein, we tested whether individual spider camouflage in the
 field better matches the chosen host leaf than the leaves chosen by
 sympatric conspecifics. To understand how camouflage is achieved, we
 tested in the laboratory whether background matching of *A. diadematus* is
 mediated by one or a combination of habitat choice by active behavioral
 selection of brown leaves on shrub vegetation and color change according
 to substrate coloration. We demonstrate that *A. diadematus* does not
 change color significantly, at least within the same instar. However,
 there is strong behavioral selection through active substrate choice
 across spiders for color-matching substrates. In general, our results
 evidenced that there is a high overlap in the diversity of brown shades
 (from pale to dark) between spider bodies and dead leaves available in the
 environment to predator vision. Spiders can also fine-tune their
 camouflage on an individual level by matching the tones (from pale to
 dark) of their host leaves. #### Date of data collection March 2022 -
 August 2022 #### Location A coastal trail between Castle
 (50°08'54" N, 05°03'26" W) and Maenporth
 (50°7'28" N, 05°05'36" W) beaches in Falmouth,
 Cornwall, Southwest UK. #### Responsible for field collections Yuri
 Fanchini Messas #### Responsible for writing the code Rafael Campos Duarte
 ## List of files * scripts: script_spider.R; * datasets:
 background_matching_data.xlsx; colour_change_rnl_data.xlsx The script
 contains the code for all analyses and figures of the study. ## Session
 info R version 4.4.0 (2024-06-14 ucrt) -- Platform: x86_64-w64-mingw32/x64
 (64-bit) ## Packages installed and their versions in R 4.4.0 colorspace
 v.2.1-1 emmeans v.1.10.5 lme4 v.1.1-35.5 lmerTest v.3.1-3 munsell v.0.5.1
 patchwork v.1.3.0 readxl v.1.4.3 rstatix v.0.7.2 tidyverse v.2.0.0 ##
 General information about the scripts and datasets The script and datasets
 refer to the analyses of the (i) color variation of European garden
 spiders (Araneus diadematus), and fresh green/dead brown leaves of their
 host plants; (ii) color variation of brown shades (from pale to reddish
 and dark) of spiders and brown leaves available in nature; (iii)
 camouflage of spiders against their brown host leaves, and against the
 mean of brown host leaves of conspecific individuals; (iv) behavioral
 choices by spiders between green and brown leaves of their host plants;
 and (v) colour change of spiders against brown and green substrates. The
 repository consists of three files, including one code script and two
 Excel files. The script contains the code to run both the statistical
 analyses and the graphics of the manuscript. ## Description of the
 datasets and variables ### DATASETS #### background_matching_data.xlsx
 This dataset contains two spreadsheets. The first spreadsheet describes
 the luminance, colour, and saturation using the RNL chromaticity space of
 spiders (*Araneus diadematus*) and the green and brown leaves of their
 host plants, as well as brown leaves of surrounding vegetation, as viewed
 by the Blue Tit (*Cyanistes caeruleus*) in the receptor noise-limited
 (RNL) chromaticity color space. The first spreadsheet also shows the
 spider coloration in the human-based RGB color space. The second
 spreadsheet contains the Blue Tit visual discrimination (as color and
 luminance JNDs) of spiders against their brown host leaves and the mean of
 brown host leaves of conspecific individuals. Column names and
 description: rnl_data image: the code used to identify each photograph
 spider_id: the identification code of each spider individual or leaf from
 each photograph, empty cells correspond to brown leaves of the surrounding
 vegetation batch: the ID of the subset of analyzed images roi: the region
 of interest (ROI) consisted of a fresh green leaf (g), a brown dry leaf
 (b), or a spider (a) lum_mean: mean luminance of ROI (relative units,
 range 0–1) lum_dev: standard deviation of luminance (relative units, range
 0–1) X_mean: mean x-axis chromaticity (RNL color space; green-red
 variation) X_dev: standard deviation of x-axis chromaticity (RNL color
 space) Y_mean: mean y-axis chromaticity (RNL color space; yellow-blue
 variation) Y_dev: standard deviation of y-axis chromaticity (RNL color
 space) saturation_mean: mean saturation saturation_dev: standard deviation
 of saturation R: red channel (RGB values, 0–255) G: green channel (RGB
 values, 0–255) B: blue channel (RGB values, 0–255) jnd spider: the code
 used to identify each spider site: the spider substrate; 'local'
 is the brown host leaf where we found the individual, 'general'
 is the mean of brown host leaves of conspecific individuals lum: Blue Tit
 luminance discrimination (JND units) colour: Blue Tit color discrimination
 (JND units) #### colour_change_data.xlsx This dataset contains two
 spreadsheets. The first describes the luminance and colour change using
 the RNL chromaticity space of brown European garden spiders (*Araneus
 diadematus*) maintained for 14 days in green or brown substrates. The
 second spreadsheet contains the calculated color JND values of spiders
 against green or brown substrates over the experimental time. Column names
 and description: colour_change image: the photo ID spider_id: the
 identification code of each individual day: days since the start of the
 experiment (days) substrate: the color of the substrate roi: the region of
 interest (ROI) consisted of a fresh green leaf (g), a brown dry leaf (b),
 or a spider (a) lum_mean: mean luminance of ROI (relative units, range
 0–1) lum_dev: standard deviation of luminance (relative units, range 0–1)
 X_mean: mean x-axis chromaticity (RNL color space) X_dev: standard
 deviation of x-axis chromaticity (RNL color space) Y_mean: mean y-axis
 chromaticity (RNL color space) Y_dev: standard deviation of y-axis
 chromaticity (RNL color space) saturation_mean: mean saturation
 saturation_dev: standard deviation of saturation jnd_change spider_id: the
 identification code of each individual day: days since the start of the
 experiment (0, 7, or 14) substrate: the color of the substrate (brown or
 green) jnd: Blue Tit color discrimination (JND units) Note: All luminance
 values are expressed in relative units normalized between 0 and 1.
 Chromaticity (X, Y) and saturation are unitless values in the RNL color
 space. JND values are unitless and represent visual discriminability for
 Blue Tit vision. RGB values range from 0 to 255. Time is measured in days.
 ### SCRIPT #### script_spider.R Contains the analyses and the codes to
 create: (i) Figure 2 showing (A) the color variation of European garden
 spiders and brown/green shrub vegetation as viewed by a Blue tit predator
 in the RNL color space, (B) the variation in the color of spiders and
 brown leaves that are available in the wild as viewed by a Blue tit
 predator in the RNL color space; (ii) Figure 3 showing Blue tit chromatic
 and achromatic visual discrimination (as JNDs) of spiders against their
 host leaves (local) and the host leaves of conspecifics (general); (iii)
 Figure 4 showing the behavioral choice of spiders between green and brown
 leaves of their host plants, considering both the foraging habitat (where
 the spider anchored its web hub) and the host leaf (where the spider
 remains hidden); (iv) Figure 5 showing the color and camouflage (as color
 JND) change of spiders maintained for 14 days on green and brown leaf
 substrates. ## Funding Sources Fundação de Amparo à Pesquisa do Estado de
 São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e
 Tecnológico (CNPq) Fundação para a Ciência e Tecnologia (FCT), Ministério
 da Ciência, Tecnologia e Ensino Superior (MCTES)