Changes in cadmium accumulation as a mechanism for cadmium resistance in the least killifish Heterandria formosa.

Evolution of resistance to heavy metals may involve complex changes at the physiological level. We report here on research into changes in cadmium uptake and accumulation as mechanisms underlying the increased resistance to Cd in laboratory lines of the least killifish, Heterandria formosa. We compared Cd accumulation between three control lines and three lines selected successfully for an increased Cd-resistance. Individuals of the Cd-adapted lines had a lower short-term (2h) uptake of Cd than those of the control lines. A time-series experiment showed that selection-line fish had a lower rate of Cd accumulation than fish from the control lines during the first 14h of exposure to 6mg/l of Cd. At the 14h time point, Cd accumulation in the control-line fish approached lethal levels, while Cd levels in selection-line fish from this point on increased at a slower rate than in the initial 14h. Overall, the relatively small changes in uptake and accumulation patterns caused lethal body burdens in the fish from the selection lines to be reached at more than twice the exposure duration at which this occurred in fish from the control lines. Lethal Cd levels appeared to be the same in control- and selection-line fish. Our results suggest that reduced uptake and accumulation of Cd accounted for approximately two-third of the increased resistance in the Cd-adapted lines.