Snakes are descended from highly visual lizards [1] , but have limited (probably dichromatic) colour vision attributed to a dim-light lifestyle of early snake ancestors [2][3][4]. The living species of front-fanged elapids, however, are ecologically very diverse, with ~300 terrestrial species (cobras, taipans, etc.) and ~60 fully marine sea snakes, plus eight independently marine, amphibious sea kraits [1]. Here, we investigate the evolution of spectral sensitivity in elapids by analyzing their opsin genes (which are responsible for sensitivity to UV and visible light), retinal photoreceptors, and ocular lenses. We found that sea snakes underwent rapid adaptive diversification of their visual pigments when compared with their terrestrial and amphibious relatives. The three opsins present in snakes (SWS1, LWS, RH1) have evolved under positive selection in elapids, and in sea snakes have undergone multiple shifts in spectral sensitivity towards the longer wavelengths that dominate below the sea surface. Several distantly related Hydrophis sea snakes are polymorphic for shortwave sensitive visual pigment encoded by alleles of SWS1. This spectral site polymorphism is expected to confer expanded 'UV-Blue' spectral sensitivity and is estimated to have persisted twice as long as the predicted survival time for selectively neutral nuclear alleles. We suggest that this polymorphism is adaptively maintained across Hydrophis species via balancing selection, similarly to the LWS polymorphism that confers allelic trichromacy in some primates. Diving sea snakes thus appear to share parallel mechanisms of color vision diversification with fruit-eating primates.

Abstract. Jaman MF, Rabbe MF, Alam MM, Shome AR, Hossain MA, Sarker MAR. 2020. Students’ perceptions on snake in Northwestern Bangladesh. Asian J Ethnobiol 21: 62-69. Human-snake interaction has an ancestral history with different outcomes at different times. This study was done to assess the student's perceptions of snakes and current superstitions practiced in some areas of northwestern Bangladesh. We interviewed 348 students from 7 educational institutions under 3 districts from January 2019 to April 2019. We asked dichotomous (yes-no) question to know perceptions about snakes and variation among superstitions of the students. We found significant variation in responses with respect to the demographic status of the respondents. Religion and education were the most influencing factors affecting the results of students’ perceptions. Among the total respondents, 329 (94.5%) had seen snakes, 182 (52.3%) considered snake as a notorious animal, 224 (64.4%) considered snakes as an economically harmful animal, 155 (44.5%) think killing snake gives a good feeling, 313 (90%) believe that snakes attack humans, 321 (92.2%) students have seen others killing snakes and 127 (36.5%) had killed snakes themselves. Of the five superstitions, “snake can drink milk” was the topmost statement believed by 293 (84.2%) students. Due to these negative attitudes and misconceptions, we assume that snakes are regularly killed and there is a potential risk for population decline.

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