Developmental Changes in the Visual Pigments of the Yellowfin Tuna, Thunnus Albacares

Previous studies have suggested that adult tunas have only two visual pigments in their retinas - a rod pigment with a wavelength at maximum absorbance ( λmax ) around 485 nm and one with similar λmax in both twin and single cones inferred from extraction data. Using microspectrophotometry we confirm the presence of a λmax 483 nm visual pigment in the rods of adult yellowfin tuna and a λmax 485 nm pigment in both members of the twin cones. However, all single cones contain a previously undetected violet visual pigment with λmax 426 nm making the adult yellowfin tuna a photopic dichromat. The situation for larvae and early juveniles is different from that of the adults. The all single-cone retina of preflexion larvae shows a wide distribution in individual cone absorbances suggesting not only mixtures of the two adult cone pigments, but the presence of at least a third visual pigment with λmax greater than 560 nm. With growth, the variation in cone absorbances decreases with convergence to the adult condition coincident with cone twinning. The significance of λmax variability, multiple visual pigment expression and age-related differences are discussed in terms of the visual ecology of larval, juvenile and adult tunas.     

Drift compensation and its sensory basis in waterstriders (Gerris paludum F.)

Summary Watestriders (Gerris paludum F.), displaced by flowing water or wind, compensate for this by periodic jumps against the direction of drift so that they keep their average position — relative to the river bank, for instance — constant over long periods of time. To identify the cues used by the animals to compensate for drift, they were kept on an artificial stream with visual patterns along one or both sides. The velocity of the water flow and the pattern motion were varied. It is not possible to induce compensatory jumps in darkness by water or air current alone. Visual cues are indispensable for the reaction. The product of jump amplitude and jump frequency equals the drift velocity on average. The jump amplitudes are more or less independent of the flow velocity while the jump frequency is adjusted to it.