A biochemical reaction associated with sex in Cladocera.

Abstract

A biochemical test for sexual differences reported by Manoilov 2 and used as the Station for Experimental Evolution by Miss Sophia Satina and others with various plants and animals, has been applied to three races of Cladocera. This is probably the first time that such a biochemical difference between the sexes has been demonstrated in a crustacean. 3

The first test with Cladocera was with small samples (0.02 gram) of females and males of Moina macrocopa. The female sample gave a faint violet coloration. The male sample gave no color. These samples, though each involving 200 or 300 individuals of this minute species, were too small to give the striking reaction obtained with more material.

The other Cladocera used were obtained from the wilds near Cold Spring Harbor. One form, a distinct type closely related to Daphnia pulex, was in an actively sexual condition. Every female was producing sexual eggs, and adult males were in the population in great numbers. A sample in duplicate of the females consisting of nearly 200 individuals was taken. A second sample was of males exclusively, about 350 individuals. A third sample was of a different type of Daphnia pulex, but obtained at the same time and from the same pond. The third sample was of a stock which was exclusively in parthenogenetic reproduction, each individual bearing numerous eggs, embryos or young in the brood chamber. The samples were of like size,-weighing 0.13 grams after the water had been removed as far as possible with filter paper. The animals were then placed in like amounts of 60 per cent alcohol (2 cc.) and the reagents applied. The sexual female sample developed a pronounced violet color. The parthenogenetic females showed the same color, but with much less intensity.