Conservation, Duplication, and Divergence of Five Opsin Genes in Insect Evolution

Abstract

Opsin proteins covalently bind to small molecular chromophores and each protein-chromophore complex is sensitive to particular wavelengths of light. Multiple opsins with different wavelength absorbance peaks are required for color vision. Comparing opsin responses is challenging at low light levels, explaining why color vision is often lost in nocturnal species. Here, we investigated opsin evolution in 27 phylogenetically diverse insect species including several transitions between photic niches (nocturnal, diurnal, and crepuscular). We find widespread conservation of five distinct opsin genes, more than commonly considered. These comprise one c-opsin plus four r-opsins (long wavelength sensitive or LWS, blue sensitive, ultra violet [UV] sensitive and the often overlooked Rh7 gene). Several recent opsin gene duplications are also detected. The diversity of opsin genes is consistent with color vision in diurnal, crepuscular, and nocturnal insects. Tests for positive selection in relation to photic niche reveal evidence for adaptive evolution in UV-sensitive opsins in day-flying insects in general, and in LWS opsins of day-flying Lepidoptera specifically.

Retinal perception and ecological significance of color vision in insects

“…The r-Opsin family in insects contains three paralogous groups with different wavelength sensitivity with absorbance peaks for the ultraviolet (UV), short (SW, blue) and long wavelengths (LW, green) [2]. Such studies suggest that the insect ancestor was a trichromat and possessed one of each of these three distinct types of Opsins (UV, SW and LW) covering a wavelength range between 300 and 700nm (Fig.…”

“…1A) [3,4,5,6]. Molecular phylogenetic analyses reveal a dynamic evolution through multiplications, functional diversification and losses of Opsin genes, especially adaptive evolution of UV-sensitive Opsins in day-flying insects in general and LW Opsins in Lepidoptera and dragonflies specifically [2,7**,8]. Coleoptera as well as arthropods closest related to insects, the Chelicerates (Spiders and scorpions), lack the blue pigment [9*,10**,11,12,13] (Fig.…”

“…1C) [7**,18,19,20]. On the other hand, nocturnal insects have often lost Opsins or have reduced Opsin expression, which can affect an entire phylogenetic branch or just a single species [2,21*]. Some insects exhibit strategies to enhance color vision or regain previously lost sensitivities for certain wavelengths.…”

The opsin repertoire of the Antarctic krill Euphausia superba

“…The role of this large number of opsins involved in visual and non-visual photoreception is still largely unknown. However, we could speculate that adaptation to complex marine and freshwater photic environments has occurred through an increase of the number of opsin genes (Feuda et al, 2016;Liegertová et al, 2015).…”

Molecular Mechanisms Underlying Color Vision and Color Formation in Dragonflies

“…17.5a). The small numbers of opsin genes in these insects may be attributed to nocturnal lifestyle of their ancestors like mammals (Briscoe and Chittka 2001;Feuda et al 2016). By contrast, almost all dragonfly species are diurnal, and they diverged from other insects over 350 million years ago (Fig.…”