Review of the firefly visual system (Coleoptera: Lampyridae) and evolution of the opsin genes underlying color vision

Abstract

Among insects, opsin copy number variation has been shown to be quite diverse. However, within the beetles, very little work on opsins has been conducted. Here, we look at the visual system of fireflies (Coleoptera: Lampyridae), which offer an elegant system in which to study visual evolution as it relates to their behavior and broader ecology. They are the best-known case of a terrestrial organism that communicates through the use bioluminescence. The molecular basis for this communication is relatively simple: one gene family (opsins) controls the detection of the signal, and one gene family (luciferase) controls the production of the signal. We use a transcriptomic approach to sample for and investigate opsin evolution in fireflies. We also use a phylogenetic estimate of Lampyridae to examine the evolution and ancestral modality of adult courtship communication. We find evidence for only two expressed opsin classes in each of the nine firefly species studied, one in the ultraviolet-sensitive and one in the long-wavelength-sensitive areas of the visible spectrum. Bioluminescent communication in adults is not optimized to be present ancestrally, and was gained two times with six subsequent losses. Despite the need for most adult fireflies to respond to a clearly sexual and colorful visual signal (bioluminescence) to maximize fitness, their visual system is relatively simple, and does not match the trend for opsin duplication found in other insect groups.

Variation in opsin genes correlates with signalling ecology in North American fireflies

“…For example, we identified luciferase transcripts, the light-producing enzyme putatively expressed only in the light organ, at a level that was three orders of magnitude lower than the LW and UV opsins. Fourth, a recently published study did not find a B opsin in the transcriptomes of nine firefly species (Martin et al 2015). Based on our data, we conclude that fireflies have lost the hypothesized ancestral insect B opsin paralog.…”

“…Fourth, a recently published study did not find a B opsin in the transcriptomes of nine firefly species (Martin et al . ). Based on our data, we conclude that fireflies have lost the hypothesized ancestral insect B opsin paralog.…”

Oculogryphus chenghoiyanae sp. n. (Coleoptera, Lampyridae): a new ototretine firefly from Hong Kong with descriptions of its bioluminescent behavior and ultraviolet-induced fluorescence in females

“…Firefly males are likely to have ultraviolet vision (Martin et al 2015, Sander and Hall 2015). Oculogryphus species, however, are only active in the night when ultraviolet light is weak or totally absent, thus no UV-fluorescence by the females.…”

Firefly genomes illuminate parallel origins of bioluminescence in beetles

“…The ancestral insect is hypothesized to have 3 visual opsins -one sensitive to long-wavelengths of light (LW), one to blue-wavelengths (B), and one to ultraviolet light (UV). Previously, two opsins, one with sequence similarity to other insect LW opsins and one with similarity to other insect UV opsins, were identified as highly expressed in firefly heads (232,233). A likely non-visual c-opsin was also detected, though not highly expressed (232,233).…”