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J. Pahlberg, A. Audzijonyte, R. Vainola, M. Lindstrom, K. Donner; Spectral Tuning and Adaptation to Different Light Environments of Mysid Visual Pigments. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1666. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Questions of spectral tuning, the relation of spectral and thermal properties of visual pigments, and evolutionary adaptation to different light environments were addressed using a group of small crustaceans of the genus Mysis as a model.
The study was based on microspectrophotometric measurements of visual pigment absorbance spectra, electrophysiological measurements of spectral sensitivities of dark-adapted eyes, and sequencing of the opsin gene retrieved through PCR.
A strong inverse correlation between Ea and max in M. relicta was found, consistent with that previously found in vertebrate visual pigments, and this was used to infer thermal noise. The conceptual signal-to-noise ratios thus calculated for pigments with different max in different light environments supported the notion that spectral adaptation works towards maximizing the signal-to-noise ratio rather than quantum catch as such. When comparing opsin sequences, a number of amino acid substitutions were found.
The consistent segregation of visual pigment absorbance spectra into shorter-wavelength "Sea" and longer-wavelength "Lake" populations in Nordic Mysis shrimps suggests that truly adaptive evolution is involved in tuning the visual pigment for optimal performance, driven by selection for high absolute visual sensitivity. Amino acid substitutions between M.relicta and M. salemaai pointed to similarities in spectral tuning sites of vertebrate and invertebrate opsins.A comparison including North American M. diluviana indicated that mysid shrimps have a small number of readily available tuning sites to shift between a "shorter"- and a "longer"-wavelength opsin.
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