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(M/MF188) Can the adaptation of Daphnia magna to environmental factors be inhibited by a dispersant ? Coors, Anja1, Hammers-Wirtz, Monika1, Ratte, Hans Toni1, 1 ABSTRACT- We investigated the combined effect of a dispersant, used in textile dyeing processes, and various environmental factors (food conditions, daphnid density and presence of Chaoborus larvae) on the biomass allocation of Daphnia magna. The environmental factors are known to induce shifts in the allocation of biomass within one brood in different Daphnia species. Low food conditions, crowding and presence of size-selective invertebrate predators as Chaoborus induce increased neonate size and decreased clutch size, whereas high food conditions and presence of planktivorous fish cause increased clutch size at the expense of neonate size. In previous ecotoxicological investigations the dispersant was detected to cause a shift in biomass allocation towards smaller neonate body size and larger clutch size. We suppose that the chemical interferes with the daphnid's reproductive allocation process in a similar manner like the environmental cues. Investigations on chemicals affecting biomass allocation in Daphnia may help understanding the regulation of this process and, in a more ecotoxicological point of view, help assessing the consequence of chemical exposure in the field. The results of our experiments indicate that in combination with variing environmental factors the dispersant didn't inhibit the adaptive response of Daphnia magna to the environmental factors. But regardless of the environmental factors, the smaller sized neonates caused by the directly opposed effect of the dispersant were always apparent. In summary, the dispersant exposure resulted not in a reduction of the adaptive response but in a reduction in the adaptive value of the response. Key words: Daphnia, biomass allocation, Chaoborus, dispersant |
