The jumping spider Saitis barbipes lacks a red photoreceptor to see its own sexually dimorphic red coloration

Abstract

Examining the role of color in mate choice without testing what colors the study animal is capable of seeing can lead to ill-posed hypotheses and erroneous conclusions. Here, we test the seemingly reasonable assumption that the sexually dimorphic red coloration of the male jumping spider Saitis barbipes is distinguishable, by females, from adjacent black color patches. Using microspectrophotometry, we find clear evidence for photoreceptor classes with maximal sensitivity in the UV (359 nm) and green (526 nm), inconclusive evidence for a photoreceptor maximally sensitive in the blue (451 nm), and no evidence for a red photoreceptor. No colored filters within the lens or retina could be found to shift green sensitivity to red. To quantify and visualize whether females may nevertheless be capable of discriminating red from black color patches, we take multispectral images of males and calculate photoreceptor excitations and color contrasts between color patches. Red patches would be, at best, barely discriminable from black, and not discriminable from a low-luminance green. Some color patches that appear achromatic to human eyes, such as beige and white, strongly absorb UV wavelengths and would appear as brighter “spider-greens” to S. barbipes than the red color patches. Unexpectedly, we discover an iridescent UV patch that contrasts strongly with the UV-absorbing surfaces dominating the rest of the spider. We propose that red and black coloration may serve identical purposes in sexual signaling, functioning to generate strong achromatic contrast with the visual background. The potential functional significance of red coloration outside of sexual signaling is discussed.

A road map of jumping spider behavior

“…This layered structure might support depth perception (Nagata et al 2012) and color vision. Depending on species, color vision can be di, tri, or tetrachromatic (De Voe 1975; Blest et al 1981; Nagata et al 2012; Zurek et al 2015; Glenszczyk et al 2022). It is thought that most salticids are dichromats, with ability to see in UV (which humans do not see).…”

“…A recently highlighted problem with many studies is that displays are assumed to flaunt the colors to watching females (Glenszczyk et al 2022). However, a lack of understanding of the spectral properties of the eyes of the salticid viewing the dance, which can vary from UV-green dichromacy to tetrachromacy, has led to numerous potentially erroneous assumptions about the functional significance of their coloration in mate choice (Glenszczyk et al 2022).…”

“…A recently highlighted problem with many studies is that displays are assumed to flaunt the colors to watching females (Glenszczyk et al 2022). However, a lack of understanding of the spectral properties of the eyes of the salticid viewing the dance, which can vary from UV-green dichromacy to tetrachromacy, has led to numerous potentially erroneous assumptions about the functional significance of their coloration in mate choice (Glenszczyk et al 2022). In rare cases, such as in Habronattus pyrrithrix (Chamberlin, 1924) (Echeverri et al 2017), studies confirm that dances are aligned to exhibit coloration visible to the potential mate; in other instances, studies confirm that they are not (Girard et al 2018; Glenszczyk et al 2022).…”

“…However, a lack of understanding of the spectral properties of the eyes of the salticid viewing the dance, which can vary from UV-green dichromacy to tetrachromacy, has led to numerous potentially erroneous assumptions about the functional significance of their coloration in mate choice (Glenszczyk et al 2022). In rare cases, such as in Habronattus pyrrithrix (Chamberlin, 1924) (Echeverri et al 2017), studies confirm that dances are aligned to exhibit coloration visible to the potential mate; in other instances, studies confirm that they are not (Girard et al 2018;Glenszczyk et al 2022). The vast majority of cases remain untested, but may explain why condition-dependent coloration does not necessarily predict mating success (see Taylor et al 2011Taylor et al , 2014.…”

Predation behavior as an indicator of jumping spider vision

“…The most notable exception among spiders are the jumping spiders (Araneae: Salticidae), in which the light sensitivity may span to the red part of the spectrum due to an increased number of opsin types (Yamashita & Tateda 1976), a shift or broadening of perceived light spectrum (Nagata et al 2012) or the presence of retinal filters (Zurek et al 2015). However, some jumping spiders have limited sensitivity to longwave light (Blest et al 1981; Glenszczyk et al 2022) and there is an ongoing debate about the diversity of visual systems in salticids. According to Land (2018), dichromacy, with “UV” and “green” opsins, is dominant in this spider family, and perception of longwave light is rather exceptional.…”