| Compound eye is the main vision organ of insect which plays a significant role in its foraging,finding mate,learning and memory,etc.The visual formation of insects is mainly dependent on a series of light sensing cells with different spectral sensitivity.The sensitivity of the cells to the spectrum is determined by the absorption spectrum of the pigment.Visual pigment consists of opsin and chromophore,and opsin is a super family with seven transmembrane domain G protein coupled receptors.Insect diversity is very rich,and by long-term light adaptation,the insect visual pigments evolve into three categories.Based on the absorption peaks of different opsin proteins,insect opsins can be assigned to three spectral classes: long-wavelenth(LW)opsin,blue(B)opsin and ultra-violet(UV)opsin.The two closely related species Tribolium castaneum and Tribolium confusum are important world stored grain pests.They have similar shape and habits and often occur mixedly.Both larvae and adults can harm flour,wheat bran,corn,rice and cereals,and also adult body scent glands can produce benzoquinone carcinogenic substances such as smelly liquid secretion.The polluted flour and other victims were agglomerate and smell,and they could not be eaten,causing a huge economic loss to agricultural production.Chemical insecticides control is an important tool for the flour beetles T.castaneum and T.confusum now.However,to improve efficiency of chemical insecticides and reduce their use amount,it is necessary to develop an economic,efficient and green method to manage them.In this study,to clarify the evolution of compound eyes and opsin genes in T.castaneum and T.confusum,both stereo microscope and scanning electron microscope examinations of compound eyes were first made in T.castaneum and T.confusum.Then,the full length of LW and UV gene was cloned by rapid amplification of cDNA ends(RACE),the sequences were aligned,and phylogenetic tree was constructed.Finally,the expression levels of opsin gene were measured using the real-time fluorescence quantitative PCR.The results showed that there were significant differences in the morphology of compound eyes of T.castaneum and T.confusum.Not only the compound eye width of T.castaneum was bigger than T.confusum,but also were the number and area of ommatidia of T.castaneum bigger than T.confusum.But there was not significant difference in their head wide between the two species.The LW and UV opsin gene were 1360 bp and 1256 bp in length,and there were 8 and 15 mutation sites in LW and UV opsin genes between species.Phylogeny incorporating other species revealed that,LW and UV opsin genes of T.castaneum and T.confusum were highly homologous,and T.castaneum were more closely related to T.confusum.The expression levels of LW and UV opsin genes in T.castaneum and T.confusum were significantly different in different development stages,high in adult stage,followed by the pupae and larvae.Also,the opsin gene expression of T.castaneum was higher than that of T.confusum.However,the expression levels of LW and UV opsin genes in T.castaneum and T.confusum were not significantly different between males and females.The evolutionary analyses of compound eye and opsin gene in T.castaneum and T.confusum lay the foundation for further study on the role of opsin in phototaxis behavior of stored-grain pests.It not only has important significance in theory,but also are there potential values in practical application,which may provide new ideas for the biological control of stored grain pests. |
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