Color vision has a profound effect on an insect's survivorship. It is not surprising therefore that many insects especially butterflies, have evolved different strategies in the modification of their visual system. Of these strategies, I explore the functional significance of opsin gene duplication and the impact of this molecular innovation on the color vision behavior of lycaenid butterflies.

In chapter 1, I trace the origin of the blue opsin duplication event and explore the contribution of opsin evolution to sexual wing color dichromatism. To address the first goal, I sequence 10 butterfly taxa from four closely-related butterfly families including three of the largest lycaenid subfamilies and found that this novel blue opsin gene duplication occurred before the radiation of the Polyommatine + Thecline + Lycaenine subfamilies. Subsequently, by using in situ hybridization of cloned opsin-encoding cDNAs, I found that all four opsin mRNAs are expressed in the eyes in a sex-specific manner. The blue- and long wave-sensitive opsin encoding mRNAs, BRh1 and LWRh, are co-expressed in female dorsal eye while the male dorsal eye only expressed the ultraviolet-sensitive opsin (UVRh) and BRh1. Consequently, the expression of BRh2 was only seen in the ventral area, an observation that agrees with a previous study, thereby confirming that BRh2 opsin encodes the 500 nm visual pigment.

In chapter 2, I address the functional significance of blue opsin gene duplication at the level of animal behavior. I demonstrate that the lycaenid Polyommatus icarus uses its duplicate blue opsin, BRh2, in conjunction with LWRh, to see color in the green part of the light spectrum extending up to 560 nm. I also found that P. icarus has a heterogeneously-expressed red filtering pigment and red-reflecting ommatidia in the ventral eye region but the animal could not discriminate colors in the red range (570-640 nm).

Because of the unique visual system of lycaenid butterflies, I put the innovations of the lycaenid butterfly visual system into an evolutionary framework in chapter 3. I began by describing the much simpler visual system of nymphalid butterflies, a visual system that closely resembles that of the ancestral butterflies, then trace the molecular changes in the opsin genes and their expression patterns, and the physiological changes in the visual receptors they encode. Lastly, I discuss the potential behavioral outcomes of the unique eye design of lycaenids.