Normalized absorbance spectra of butterfly visual pigments based upon the Bernard template (see Palacios et al., 1996) and wavelengths of peak absorbance (λ_max) estimated from either microspectrophotometry or intracellular recordings. (A) The compound eye of the nymphalid Danaus plexippus contains three photopigments (P) with λ_max values corresponding to 340 nm (gray), 435 nm (purple) and 545 nm (orange), respectively. Estimates of theλ _max values of the UV (P340) and B (P435) photopigments are from electrophysiological recordings (Stalleicken et al., 2006) and for the LW (P545) photopigment, from microspectrophotometric measurements (Frentiu et al., 2007a). (B) The eye of the lycaenid Lycaena rubidus contains four photopigments: P360 (gray), P437 (purple), P500 (blue), P568 (orange). Estimates of theλ _max values are from microspectrophotometric measurements (Bernard and Remington, 1991). (C) The eye of the papilionid Papilio xuthus contains five photopigments: P360, P460, P515, P530 and P575. Estimates of theλ _max values are from the intracellular recordings (Arikawa, 2003). (D) The eye of the pierid Pieris rapae contains four photopigments: P360 (gray), P425 (violet), P453 (purple) and P563 (orange). Estimates of theλ _max values are from intracellular recordings (Qiu and Arikawa, 2003a; Qiu and Arikawa, 2003b) (see also Wakakuwa et al., 2004; Arikawa et al., 2005).

Phylogenies of the UV, B and LW opsin genes of each of the five butterfly families including genes corresponding to the visual pigments shown in Fig. 2. The neighbor-joining method using 1st+2nd nucleotide positions and the Tamura-Nei model of evolution was used. Numbers represent the percentage of trees in which a particular node was recovered out of 500 replicates. The moths Manduca sexta (Sphingidae) and Bombyx mori (Bombycidae) are used as outgroups. (A) UV opsin gene tree. Opsin genes encoding the UV-absorbing visual pigments in Fig. 2 are indicated by bold gray. In each of the butterfly species shown, the UV visual pigment is encoded by a single-copy gene. The full-length UV opsin cDNA of A. mormo is newly presented in this study (GenBank accession no. AY587905). (B) B opsin gene tree. Opsin genes encoding the B-absorbing visual pigments in Fig. 2 are shown in bold purple. Duplications of the B opsin gene have been observed twice in independent butterfly lineages: once in the pierid P. rapae giving rise to the violet receptor (PrV) (light purple) (Arikawa et al., 2005), and once in the lycaenid L. rubidus, giving rise to a blue–green (B2)-sensitive photopigment (BRh2; blue) (Sison-Mangus et al., 2006). (C) LW opsin gene tree. Opsin genes encoding the LW-absorbing visual pigments shown in Fig. 2 are indicated by bold orange, yellow and green. LW opsin gene duplications have occurred in three of five butterfly families independently. Besides those in Papilio, LW opsin duplicate genes have been recovered from the eye of the riodinid Apodemia mormo and from the genomic DNA of the nymphalid Hermeuptychia hermes (not shown) (Frentiu et al., 2007a). Scale bars indicate substitutions per site.

Ommatidial subtypes found in the dorsal rim area (DRA), dorsal and ventral retina of butterflies according to opsin mRNA expression in individual R1–8 photoreceptor cells (ovals). Photoreceptor cells are color coded according to the identically colored visual pigments and opsins shown in Figs 2 and 3 that are expressed in them. Question mark indicates that opsin expression is unknown in some parts of the eyes reviewed here. Boxes indicate the UV, B and LW opsin genes and lineage-specific duplicates present in each species and are organized into columns according to membership in the UV, B or LW opsin clades shown in Fig. 2. Note: the patterns of opsin mRNA expression in the riodinid Apodemia mormo are unknown and so are not included in this scheme. Left to right: D. plexippus DRA is composed of approximately 100 ommatidia organized into two to three rows that exclusively express the UV opsin (gray) in the R1–8 cells. Both the dorsal and ventral eye contain three types of ommatidia in which the R1 and R2 cells express UV–UV, UV–B or B–B opsin mRNAs and the R5–8 cells express a LW opsin (orange) (Sauman et al., 2005). P. rapae ventral eye contains four opsins and three ommatidial subtypes in which R5–8 express one LW opsin mRNA (orange) and R1 and R2 express UV–B, UV–UV or V–V (violet) opsin mRNA (Arikawa et al., 2005). It is not yet known whether other ommatidial subtypes are present in the dorsal retina or in the DRA. L. rubidus dorsal eye contains three opsins and is sexually dimorphic with respect to their expression. In males, R5–8 exclusively expresses the B1 (purple) opsin, while in females the B1 opsin is co-expressed with the LW (orange) opsin. The R1 and R2 cells of the dorsal eye are almost entirely UV–UV, with the R1 and R2 cells of a few ommatidia expressing UV–B1 and even fewer expressing B1–B1. The ventral eye of both males and females contains one additional opsin, B2, encoded by a duplicate blue opsin gene, BRh2. The R3–8 cells all express the LW opsin and R1 and R2 all express UV–B1, UV–UV, B1–B1, UV–B2, B1–B2 or B2–B2 (Sison-Mangus et al., 2006). P. xuthus contains a dorsal eye with four opsins and three distinct ommatidial subtypes: B–B (dark purple) in R1 and R2 and PxRh2 (orange) in R3–8; UV–B in R1 and R2, PxRh2 in R3 and R4, and PxRh3 (yellow) in R5–8; UV–UV (gray) in R1 and R2, PxRh2 in R3 and R4, and co-expressed PxRh2 and PxRh3 (orange–yellow). The ventral retina contains five opsins and the same three ommatidial subtypes except PxRh1 is co-expressed with PxRh2 (green–orange) in all R3 and R4 cells in the ventral eye. Squares indicate opsin genes expressed in identically colored photoreceptor cells.

Diagram of an ommatidium and opsin mRNA expression in the swallowtail butterfly Papilio glaucus, newly presented here. Methods used for the in situ hybridizations are as detailed previously (Briscoe et al., 2003). (A) Longitudinal view of an ommatidium. In Papilio spp., the photoreceptor cell bodies that contribute to the fused rhabdom are organized into three tiers: I, II and III. c, cornea; cc, crystalline cone; n, photoreceptor nucleus; L, lamina; M, medulla. (B) Tangential views of an ommatidium. The most distal tier (I) contains the cell bodies of the R1 and 2 and R3 and 4 cells. The proximal tier (II) contains the cell bodies of the R5–8 cells, and the basal tier (III) contains the R9 cell body. Gray indicates the identity of the photoreceptor cells in which specific opsin mRNA expression is shown in the panels to the right. (C) Digoxigenin-labeled antisense riboprobe of UV (PglRh5) indicating the expression of this opsin mRNA in the distal tier of photoreceptor cells. This opsin is homologous to the UV opsin gene of P. xuthus, PxUV, shown in Fig. 2. (D) A semi-tangential section showing double labeling of R1 and R2 cells with antisense biotin-labeled UV (PglRh5) (brown) and digoxigenin-labeled B opsin mRNA (PglRh6) (blue). The latter is homologous to the blue (B) opsin gene of P. xuthus, PxB, shown in Fig. 2. Three subtypes of ommatidia are evident: UV–UV, UV–B and B–B. (E) UV opsin expression (red) in R1 and R2 cells using a rabbit anti-PglRh5 peptide antibody generated by the author (see Lampel et al., 2005) and visualized with a Cy3-conjugated goat anti-rabbit secondary antibody. Tangential section showing opsin staining in both the rhabdom (white arrow) and cytoplasm. Two subtypes of ommatidia are shown here, UV–UV and UV–?, although all three subtypes implied by D are present elsewhere in the section. (F) Tangential section of the ventral retina showing staining of all R3 and R4 cells with a digoxigenin-labeled antisense PglRh1 riboprobe. PglRh1 is homologous to P. xuthus PxRh1 shown in Fig. 2. (G) Tangential view of an adjacent section to F of the ventral retina showing staining of all R3 and R4 cells with digoxigenin-labeled antisense PglRh2 riboprobe, and indicating co-expression of PglRh1 and PglRh2 in these cells in the ventral retina. In the dorsal eye, only PglRh2 is present in the R3 and R4 cells (data not shown). (H) Longitudinal section of the eye indicating staining of the proximal (R5–8) tier of photoreceptor cells with a digoxigenin-labeled antisense riboprobe to PglRh3. (I) Tangential section showing strong staining of the R5–8 cells (arrow) of some ommatidia with a digoxigenin-labeled anti-sense riboprobe to PglRh3. (J) Tangential section showing strong staining of the R5–8 cells (arrow) of some ommatidia with a digoxigenin-labeled antisense riboprobe to PglRh2. (K) Dissociated ommatidium in which the R9 cell (arrow), but not the adjoining R5–8 cells, is clearly stained with a digoxigenin-labeled antisense riboprobe to PglRh2. This represents one (Type I) of three ommatidial subtypes defined by Arikawa (Arikawa, 2003). (L) Dissociated ommatidium in which both the R9 cell (arrow) and the R5–8 cells are clearly stained with a digoxigenin-labeled antisense riboprobe to PglRh2. This ommatidial subtype corresponds to either the Type II or Type III subtype (Arikawa, 2003).