Absorption properties of rhodopsin in three species of Sepioteuthis spp.

Abstract

　The three species of Sepioteuthis spp. inhabiting the waters off the coast of Japan frequently appear in different areas and depths. We isolated the rhodopsin gene, and also compared the wavelength sensitivity of these squid species by measuring the maximum absorption wavelength (λ_max). The full length of the rhodopsin gene for all three species was 1356 bp and was translated into 452 amino acid residues. The λ_max value was 496, 492, and 489 nm for S. sp. 1, S. sp. 2, and S. sp. 3, respectively, with S. sp. 1 from the deepest habitat showing the longest wavelength, opposite to the typical depth-related trend. In general, the λ_max value of aquatic animals is shorter for those inhabiting deeper waters. It is suggested that the difference of about 100 m between the three Sepioteuthis spp. may not be reflected in the rhodopsin λ_max.