SOMATIC POLYPLOIDY EXAMINED BY FLOW-CYTOMETRY IN DAPHNIA

Flow cytometry was used to examine the patterns of somatic polyploidy and to determine the haploid genome sizes in Daphnia. The average prop ortions of polyploid nuclei among adult animals of D.pulex, D.longispi na, D.pulex x D.longispina and D.magna equalled 27, 24, 24 and 24%, re spectively. Both interclonal and developmentally regulated variation w ere observed in the level of somatic polyploidy. Adult animals express ed more extensive polyploidy than did juveniles. The estimates of the haploid genome sizes (C values) of D.pulex, D.longispina, D.pulex x D. longispina and D.magna equalled 0.32, 0.27, 0.26 and 0.37 pg, respecti vely. These are the smallest genomes reported in crustaceans. Apparent ly, somatic polyploidy compensates for the loss of genetic material an d gives rise to genetic plasticity which may contribute to the conside rable level of phenotypic plasticity observed in Daphnia.