Data from: Background matching, disruptive coloration and differential use of microhabitats in two neotropical grasshoppers with sexual dichromatism
Cite this dataset
Ramírez-Delgado, Víctor Hugo; Cueva del Castillo, Raúl (2020). Data from: Background matching, disruptive coloration and differential use of microhabitats in two neotropical grasshoppers with sexual dichromatism [Dataset]. Dryad. https://doi.org/10.5061/dryad.vhhmgqnpx
Abstract
Cryptic coloration is an adaptative defensive mechanism against predators. Color patterns can become cryptic through background coloration-matching and disruptive coloration. Disruptive coloration may evolve in visually heterogeneous microhabitats, whereas background matching could be favored in chromatically homogeneous microhabitats. In this work, we used digital photography to explore the potential use of disruptive coloration and background matching in males and females of two grasshopper species of the Sphenarium genus in different habitats. We found chromatic differences in the two grasshopper species that may be explained by local adaptation. We also found that the females and males of both species are dichromatic and seem to follow different color cryptic strategies, males are more disruptive than females, whereas females have a high background matching with less disruptive elements. The selective pressures of the predators in different microhabitats and the differences in mobility between sexes may explain the color pattern divergence between females and males. Nevertheless, more field experiments are needed in order to understand the relative importance of disruptive and background matching coloration in the evolution of sexual dichromatism in these grasshoppers.
Methods
Pattern analysis
We performed a granularity analysis based on the Fast Fourier bandpass filtering to evaluate the color patterns. Bandpass filters allow information at different spatial scales to be separated (for details see Chiao et al., 2009; Stoddard and Stevens, 2010). We used the average pixel reflectance of red and green channels to calculate the energy spectrum of grasshoppers and their background across 15 filters ranging from 2 pixels to 256 pixels, in increments of multiples of √2. We obtained three descriptive variables from the energy spectrum: the maximum energy peak of the spectrum (emax), the filter size where emax is reached (Filtermax), and the proportion of the emax compared to the rest of the spectrum (eprop), which respectively indicate contrast of the dominant marking, marking size and pattern diversity.
Color background matching analysis
Color background matching was evaluated by measuring individual pixel reflectance and calculating the mean reflectance values of the multispectral image for the three channels (RGB) for the grasshoppers and their backgrounds. Spectral images are in a 16-bit scale, given this image format, the reflectance values range from zero to 65535.
Disruptive coloration
We evaluated the edge disruption of grasshoppers using GabRat tool implemented in MICA toolbox. GabRat tool measured the ratio between false and coherent edges of the grasshoppers’ surfaces. For the GabRat analysis we use the multispectral image used in the granularity analysis. We obtained the GabRat values from the photographs of grasshoppers’ dorsal surface. For this analysis the size of the Gabor filter (sigma) ideally should match the acuity of the possible viewers in order to be effective. In this study we use a sigma value = 5 because it has been informative in analysis where the objects were scaled close to 17 pixels per mm (Troscianko, Skelhorn and Stevens, 2018; Price et al., 2019).
We obtained the GabRat value for R, G, B channels of the multispectral images, subsequently we obtained the mean GabRat ( average GabRat) of the three channels for every grasshoppers’ photograph.
Usage notes
Excel file contains:
Table S1. Data for the pattern analysis.
Table S2. Data for the color means analysis.
Tabla S3. Data for the coloration disruptive analysis.
Funding
Consejo Nacional de Humanidades, Ciencias y Tecnologías, Award: 330551
Universidad Nacional Autónoma de México, Award: PAPIIT-UNAM IN211617