Evolution of color vision in insects

Meeting Abstract

S4.7  Monday, Jan. 5  Evolution of color vision in insects BRISCOE, AD; Univ. of California, Irvine abriscoe@uci.edu

The eyes of insects are remarkable. Much of eye diversity can be traced to alterations in the number, spectral properties, and spatial distribution of the visual pigments. Visual pigments are light-sensitive molecules composed of an opsin protein and a chromophore. Most insects have eyes that contain visual pigments with a wavelength of peak absorbance, lambda-max, in the ultraviolet (UV)(300-400 nm), blue (B)(400-500 nm) and long wavelength (LW)(500-600 nm) part of the visible light spectrum, respectively, encoded by distinct UV, B and LW opsin genes. Most of what we know about the molecular basis of vision in insects is based upon studies of holometabolous insects. In the compound eye of flies, bees, moths and butterflies, each individual ommatidium is composed of eight or nine photoreceptor cells (R1-9) that generally express only one opsin mRNA per cell, although in some fly and butterfly eyes, there are ommatidial subtypes in which two opsins are co-expressed in the same photoreceptor cell. Based on a phylogenetic analysis of opsin sequences from red flour beetle, honey bee, silkmoth, and butterflies, and comparative analysis of opsin gene expression patterns, I propose a model for the patterning of the ancestral holometabolous insect eye that is most closely aligned with the honey bee and butterfly eye. The R1 and R2 cells of the main retina expressed either UV-UV, UV-B or B-B absorbing visual pigments while the R3-9 cells expressed an LW-absorbing visual pigment. Visual systems of existing insects then underwent an adaptive expansion based on lineage-specific UV, B and LW opsin gene multiplications and on alterations in the spatial expression of opsins within the eye. In at least two instances, that of the fly and red flour beetle, this has also involved the loss of the blue-green and B opsin genes, respectively. Understanding the molecular sophistication of insect eye complexity is a challenge, which if met, has broad biological implications.

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