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L.M. Garner, C. Anderson, D. McElroy, J. Bilotta; Differences in Spectral Sensitivity of ERG b- and d-waves in Three African Cichlid Fish Species . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4169.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous studies indicate that African cichlid fish species express alternative combinations of five ancestral cone types, with peak sensitivities at 369, 447, 488, 533 and 570 nm (U-, S1-, S2-, L1- and L2- cones, respectively). Because many hypotheses relating to cichlid ecological divergence, sexual selection and speciation assume a primary role for coloration, it is essential to derive an empirical understanding of the range and sensitivity of the visual system. The purpose of this study was to determine the cone contributions to the photopic spectral sensitivity of the electroretinogram (ERG) b- and d-wave responses of three African cichlid species from Lake Malawi, Aulonocara jacobfreibergi 'lemon', A. stuartgranti 'blue neon', and Metriaclima thapsinogen. Methods: ERG responses to visual stimuli, which consisted of 500 ms flashes of various wavelengths (320 to 700 nm) and irradiances, were recorded. Spectral sensitivity functions were calculated from the irradiance verses response amplitude functions of ERG b- and d-waves obtained under a variety of broadband and chromatic backgrounds. Results: The spectral sensitivity function of the b-wave component indicates variations in cone type contributions among the three species. M. thapsinogen and A. jacobfreibergi show contributions of at least four cone types (U-, S2-, L1- and L2-cones); nevertheless, A. jacobfreibergi shows stronger U-cone and weaker S2-cone contributions than does M. thapsinogen. By contrast, A. stuartgranti appears to lack L1-cones. ERG d-wave responses appear largely similar among the three species, but differ from the b-wave responses in that the d-wave receives no more than three cone type contributions. Cone contribution results were consistent across all chromatic backgrounds. Conclusions: While clear differences in cone contributions exist across the three species, there was no obvious phylogenetic component to these differences. This suggests that analyses of visual sensitivities may prove useful in examining the role of coloration as a communication signal involved in driving the evolutionary dynamics of African cichlid fishes. Also of interest are the systematic differences between b- and d-wave responses, which may suggest different roles of the two ERG components in visual processing.
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