Some Effects of Colchicine on Heredity in Daphnia Longispina.

HE success of BLAKESLEE and AVERY (1937) and of NEBEL and T RUTTLE (1938) in inducing polyploidy in plants by means of colchicine treatments has been followed by investigations of other plant materials by a number of workers (EIGSTI 1938, WALKER 1938, DERMEN 1939, LEVAN 1938, and RASMUSSON and LEVAN 1939). While polyploid plants have been obtained by treating diploid plants with colchicine, apparently no workers with animal materials have reported the production of polyploid animal forms by the use of the drug. Naturally occurring polyploidy is rare in animals but quite common among plants. DOBZHANSKY (1937, p. 219) states that “the prevalence of the polyploid series of chromosome numbers in plants and their relative scarcity among animals constitutes the greatest known difference between the evolutionary patterns in the two kingdoms.” During the summer of 1937 the authors became interested in the problem of treating the parthenogenetic eggs of a cladoceran with colchicine. It was hoped that colchicine might produce results in the developing diploid parthenogenetic egg of a cladoceran that would be comparable with results already obtained in plants. It seemed theoretically possible to induce tetraploidy in the developing parthenogenetic egg and thereby obtain a tetraploid clone of Cladocera. Presumably a tetraploid cladoceran, if obtained, could readily be propagated by parthenogenesis. Tetraploid or polyploid bisexual animals, for example Drosophila, have been shown to yield many sterile intersexes among their offspring-a fact commonly explained by the chromosome balance theory of sex determination (BRIDGES