Nanoscale ultrastructures increase the visual conspicuousness of signalling traits in obligate cleaner shrimps

To be effective, signals must be detectable; thus, signal theory predicts that organisms should evolve signals that are conspicuous to intended receivers in natural signalling environments. Cleaner shrimps remove ectoparasites from reef fish clients and many signal their intent to clean by whipping their long, white antennae. Since white is a reliably conspicuous colour in aquatic environments, we hypothesized that selection has acted to increase broad-spectrum antennal reflectance in these species. We compared reflectance and antennae ultrastructure in three obligate cleaner species with one facultative cleaner and one non-cleaner in two families (Palaemonidae and Lysmatidae). Obligate cleaner antennae had a reflectance of 41-52% of human-visible light, compared to 35% in the facultative cleaner and 21% in the non-cleaner. Scanning electron microscopy (SEM) revealed the antennae in two obligate cleaner species contain a layer of densely packed, high refractive index spheres (300-400nm ..., Reflectance Measurements
We used calibrated photography under a stereomicroscope to measure reflectance from the antennae following methods in [22]. Calibrated photography was used instead of spectoradiometry because cleaner shrimp antennae are cylindrical rather than flat, causing light to scatter in directions that are not captured by the fibre optic sensor, likely underestimating reflectance. In brief, photographs of antennae were taken with an iPhone (model 13, Apple Inc., Cupertino, CA) and included a reflectance standard comprising five grey paint swatches of measured reflectance. We measured the 0-255 value from each swatch of the grey standard (using the image analysis software Fiji [23]), using only the green channel of the sRGB image. The green channel was used both to approximate as closely as we are able brightness vision in particular, and because of the three colour channels, it is most closely aligned with the ambient illuminant on a coral reef [24]. We then plotted the g..., , # READ ME GUIDE TO SUPPLEMENTAL DATA AND CODE FILES

Caves et al., Nanoscale ultrastructures increase the visual conspicuousness of signalling traits in obligate cleaner shrimps. Journal of Experimental Biology.

R_code.R:

-An R script which runs all of the analyses and creates all of the figures in the manuscript and extended data.

-Three files are necessary to run the complete R script:

1\) `Reflectance_calibrated_photography.csv`: this file contains reflectance data generated using calibrated color photography, for various species of shrimps

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Columns are:

-Species: Shrimp species

-Specimen: a number indicating which individual of a given species reflectance values are taken from

-Measurement: multiple measurements were taken per individual; this column indicates which measurement number a reflectance value is associated with

-Reflectance: measured reflectance in percent

-Type: Shrimp type (either “cleaner”, “facultative cleaner”, “or non cleaner”)

-Category: A cat...