Light-induced swimming of Daphnia: can laboratory experiments predict diel vertical migration?

Vertical displacement velocity of a Daphnia galeata x hyalina clone was quantified in relation to changes in the relative rate of light change. An increase in the latter variable triggers an enhanced swimming response, and this response is again elicited when a second increase in the rate of relative light increase is applied. Decreases in the rate of light increase affect phototactic swimming in a similar way. The acceleration/deceleration assisted stimulus-response system is an extension of the idea of phototaxis as the underlying behavioural mechanism for vertical migration, and suggests that continuous accelerations in light change also affect vertical displacements observed in the field. A simple diel vertical migration simulation model was used to calculate the vertical displacement of Daphnia in relation to the natural light change at sunrise. The calculated vertical displacement fits nicely in the temporal range of the observed averaged downward migration of adult Daphnia in Lake Maarsseveen. The calculated migration amplitude, however, is larger than the change in mean population depth observed in nature. [KEYWORDS: Daphnia; phototaxis; swimming behaviour; diel vertical migration; model Galeata x hyalina; phototactic behavior; magna; genotype;clones