| Vision is one of the most important ways to perceive ambient enviorenment in animals. The visual systems in animals vary among species as a consequence of adaptive evolution. Although the visual systems are phenotypically diverse, the sensitivity of animals to visual signals is based on the same kind of substance, the visual pigements. A visual pigment is composed of an opsin apoprotein and a Vitamin A-derived chromophore, the chromophore attach to Lys residue covalently in the seventh transmembrane of the opsin apoprotein through a Schiff's base linkage, responses for light activation. Visual pigments are often characterized by the wavelength of maximal absorption(λmax). The spectral sensitivity of a visual pigment is tuned by specific interactions between the chromophore and the side chains of transmembraneα-helixes of opsin apoprotein. As most visual pigments recruit the same chromophore in animals, observed variation inλmax of a visual pigement is caused by variation in opsin sequence.The opsin family holds a lot of members, with some related to the visual system, and many non-visual opsins expressed in different tissues of animals. According to the wavelength of maximal absorption, vertebrate opsins could be distinguished as five classes: LWS, SWS1, SWS2, Rh2 and Rh1. Insect opsins are characterized in a similar way. Following the divergence of the ancestral vertebrate and invertebrate species, about 700 millions years ago, the ancestral opsin gene underwent a series of independent duplication events, producing several kinds of genes encoding different opsins. In the evolutionary history of animals, diffrent opsin gene lineages diversified by gene losses, gene duplications and function-altering amino acid substitutions.Insects occupy diverse niches in nature and have different behaviour patterns, and relevant adaptive evolution arises in their visual systems. In the mutualism system of fig wasps and their host figs, the light environment in which fig wasps live is very special. Generally, male fig wasps spend all their lives in the syconium of fig, and they have vestigial eyes and no ocelli. However, the female fig wasps have to emerge from the fig syconium and search for another syconium to finish the process of pollination and oviposition, and they have developed compound eyes. The enclosed syconium seems to be a complete dark cavity, with no light signals existing inside, especially for the weak-penetrable UV light. UV light plays a great role in many animals. For example in the bees, which are phylogenetically close related to fig wasps, UV is proved to be responsible for flowers detecting and recognizing, polarized vision and flying orientation. As a consequence of adaptation to the light environment in which they live, the UV sensitive opsins of fig wasps may have evolved in a special way.Does UV light play a role in the vison of fig wasps? Are the UV sensitive opsin genes restricted to figs? Is there any diference in this gene between the pollinators and non-pollinating fig wasps? To figure out these questions, we cloned a full-length UV sensitive opsin gene cDNA from a fig wasp species and partial UV sensitive opsin gene cDNA sequences from other 13 fig wasp species. These 14 fig wasp species are hosted in four different fig species. Comparision and phylogenetic analysis of these sequences indicates they belong to the UV sensitive opsin gene lineage, encode opsins which are responsible for UV light. Most of the UV opsins in fig wasps are too conservative and show a pattern of convergent evolution, so they seem to be unsuitable as a molecular marker for phylogenetic analysis. We also conducted selection test analysis and ancestral-state reconstruction. Two sites were found to be under positive selection, but no parallel or convergent change was observed. This suggests that UV sensitive opsin genes in fig wasps are under weak positive selection.
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