Not all butterfly eyes are created equal: Rhodopsin absorption spectra, molecular identification, and localization of ultraviolet‐, blue‐, and green‐sensitive rhodopsin‐encoding mRNAs in the retina of Vanessa cardui

Abstract

Surveys of spectral sensitivities, visual pigment spectra, and opsin gene sequences have indicated that all butterfly eyes contain ultraviolet-, blue-, and green-sensitive rhodopsins. Some species also contain a fourth or fifth type, related in amino acid sequence to green-sensitive insect rhodopsins, but red shifted in absorbance. By combining electron microscopy, epi-microspectrophotometry, and polymerase chain reaction cloning, we found that the compound eye of Vanessa cardui has the typical ultrastructural features of the butterfly retina but contains only the three common insect rhodopsins. We estimated lambda-max values and relative densities of the rhodopsins in the Vanessa retina (0.72, P530; 0.12, P470; and 0.15, P360) from microspectrophotometric measurements and calculations based on a computational model of reflectance spectra. We isolated three opsin-encoding cDNA fragments that were identified with P530, P470, and P360 by homology to the well-characterized insect rhodopsin families. The retinal mosaic was mapped by opsin mRNA in situ hybridization and found to contain three kinds of ommatidia with respect to their patterns of short wavelength rhodopsin expression. In some ommatidia, P360 or P470 was expressed in R1 and R2 opposed receptor cells; in others, one cell expressed P360, whereas its complement expressed P470. P530 was expressed in the other seven cells of all ommatidia. P470-expressing cells were abundant in the ventral retina but nearly absent dorsally. Our results indicated that there are major differences between the color vision systems of nymphalid and papilionid butterflies: the nymphalid Vanessa has a simpler, trichromatic, system than do the tetrachromatic papilionids that have been studied.

Beauty in the eye of the beholder: the two blue opsins of lycaenid butterflies and the opsin gene-driven evolution of sexually dimorphic eyes

“…Procedures for using an epi-microspectrophotometer to make photochemical measurements from butterfly eyeshine were previously described (Bernard, 1983a;Bernard, 1983b;Briscoe et al, 2003;Briscoe and Bernard, 2005). Briefly, an intact Lycaena rubidus (Lycaenidae) (either female or male) was mounted in a slotted plastic tube fixed to the goniometric stage, then oriented to set the eye's direction of view to elevation 40°and azimuth 15°.…”

“…Approximately 0.05· g riboprobe per l hybridization buffer was hybridized to the histologic sections overnight at 60°C. Washing, detection and mounting methods are as described (Briscoe et al, 2003). Slides were viewed under an Axioskop microscope (Zeiss, Thornwood, NY, USA) using bright field illumination.…”

“…We next estimated the visual pigment content of the male and female dorsal eyes from experimental reflectance spectra using epi-microspectrophotometric methods, as described (Bernard, 1982;Bernard, 1983a;Bernard, 1983b;Bernard and Remington, 1991;Briscoe et al, 2003). A computational analysis of these spectra revealed two short-wavelength visual pigments in the dorsal eyes of both sexes ( max =360 and 437·nm) (Fig.·2E-H).…”

“…We note that the short wavelength opsins have a lysine at residue 112 (UVRh) and a glutamate at residue 107 (BRh1 and BRh2), which confer UVabsorbing (lysine) and blue-absorbing (glutamate) spectra (Salcedo et al, 2003). The situation in L. rubidus differs markedly from that of the nymphalid butterflies Vanessa cardui or the monarch Danaus plexippus, in which only three opsin mRNAs are expressed (UV, B, and LW) in the photoreceptor cells of the adult eye (Briscoe et al, 2003;Sauman et al, 2005), or that of the swallowtail butterfly, in which three duplicate LW opsin genes are expressed (Briscoe, 1998;Kitamoto et al, 1998). The L. rubidus opsin expression pattern does, however, resemble the situation in Pieris rapae, in which duplicate B opsin genes are also expressed in the eye (Arikawa et al, 2005) (but see below).…”

“…Most lepidopteran eyes contain a minimum of three visual pigments with absorbances that peak at ~350·nm (UV), 440·nm (blue, B) and 530·nm (long wavelength, LW) (reviewed in Briscoe and Chittka, 2001). In the sphingid moth, the painted lady and monarch butterfly, these visual pigments are encoded by paralogous UV, B and LW opsin genes, which were present in the ancestor of all lepidopterans (Briscoe et al, 2003;White et al, 2003;Sauman et al, 2005). Deviations from this basic plan have been described in the most primitive of butterfly families, the papilionids, in which two rounds of duplication of the LW eye opsin gene have occurred (Briscoe, 1998;Kitamoto et al, 1998;Briscoe, 2001); and in the pierids, in which a duplicate blue opsin gene has been reported (Arikawa et al, 2005).…”