Molecular evidence for color discrimination in the Atlantic sand fiddler crab, Uca pugilator

Abstract

SUMMARYFiddler crabs are intertidal brachyuran crabs that belong to the genus Uca. Approximately 97 different species have been identified, and several of these live sympatrically. Many have species-specific body color patterns that may act as signals for intra-and interspecific communication. To understand the behavioral and ecological role of this coloration we must know whether fiddler crabs have the physiological capacity to perceive color cues. Using a molecular approach, we identified the opsinencoding genes and determined their expression patterns across the eye of the sand fiddler crab, Uca pugilator. We identified three different opsin-encoding genes (UpRh1, UpRh2 and UpRh3). UpRh1 and UpRh2 are highly related and have similarities in their amino acid sequences to other arthropod long-and medium-wavelength-sensitive opsins, whereas UpRh3 is similar to other arthropod UV-sensitive opsins. All three opsins are expressed in each ommatidium, in an opsin-specific pattern. UpRh3 is present only in the R8 photoreceptor cell, whereas UpRh1 and UpRh2 are present in the R1-7 cells, with UpRh1 expression restricted to five cells and UpRh2 expression present in three cells. Thus, one photoreceptor in every ommatidium expresses both UpRh1 and UpRh2, providing another example of sensory receptor coexpression. These results show that U. pugilator has the basic molecular machinery for color perception, perhaps even trichromatic vision.

The male blue crab,Callinectes sapidus, uses both chromatic and achromatic cues during mate choice

“…True color vision has been infrequently documented in crustaceans. Certainly, spectral sensitivity and the presence of different spectral classes of photoreceptors have been widely documented across crustacean species (Cronin and Forward, 1988;Frank and Widder, 1999;Rajkumar et al, 2010), but the behavioral evidence needed to confirm color vision (and discount confounding achromatic cues) is not common. Aside from tests in C. sapidus, color vision has been demonstrated in a fiddler crab, Uca mjoebergi, where females chose males with painted yellow claws over those with claws painted various shades of gray (Detto, 2007).…”

Extraordinary diversity of visual opsin genes in dragonflies

“…Conventionally, it has been envisaged that, on the basis of vertebrate studies, each photoreceptor cell expresses a single opsin gene, and multiple photoreceptor cells expressing several different opsin genes with different absorption spectra constitute a retina for color vision (30,31,33,34). However, recent studies have identified coexpression of multiple opsin genes in a single photoreceptor cell in compound eyes of butterflies and other arthropods (67)(68)(69)(70), raising the possibility that such opsin coexpression may enrich the photoreceptor diversity among invertebrates including dragonflies.…”

Spectral sensitivity, spatial resolution, and temporal resolution and their implications for conspecific signalling in cleaner shrimp

“…However, an expressed opsin does not necessarily have any functional significance in vision (for example, in the onycophoran Euperipatoides kanangrensis; Eriksson et al, 2013). Additionally, many crustaceans express more opsins than would be predicted based on photoreceptor physiology, as has been shown in stomatopods (Porter et al, 2013), brachyuran crabs (Rajkumar et al, 2010;Sakamoto et al, 1996), mysids (Frank et al, 2009), ostracods (Oakley and Huber, 2004) and branchipods (Kashiyama et al, 2009). Retinal transcriptomes, however, could be used to provide evidence for functional, expressed opsins.…”