Food and Crowding as Sex Controlling Factors in Cladocera

Abstract

In an attempt to show that crowding and the subsequent accumulation of excretory products were not essential for the production of males by Cladocera, Stuart and Cooper 1 reared isolated Moina mothers in from 100 to 500 ml. of very dilute manure infusion medium. 2 It was found that isolated mothers reared in as large a volume as 500 ml. of suitably diluted medium not infrequently produced males. It seemed of interest then to ascertain whether or not crowded mothers reared in exceedingly small volumes of concentrated or heavily bacterized medium 3 would produce female young.

After many preliminary experiments, the following procedure was selected: Manure infusion medium 3 or manure infusion to which filtrate of mascerated Cladocera (“cell juice”) had been added was dispersed in 2 ml. amounts in 15 × 5 mm, vials. Ten young sister Cladocera (Moina macrocopa) were placed in each vial. The cell juice was prepared by collecting several thousand Cladocera with embryos or eggs in the brood chamber and grinding them up in a mortar in a small amount of pond water, then filtering the resulting extract through paper. The medium was bacterialized by the addition of one drop of a concentrated suspension of Aero-bacter aerogenes. 3 The bacterization was repeated at from 4 to 8 hour intervals until the animals laid eggs, at which time the 10 mothers were placed in 100 ml. of normal culture medium to release their young. As controls 10 mothers, sisters of those in the vials, were reared in the usual 100 ml. of unbacterized medium in the usual 6 oz. bottles. When the mothers released, the number and sex of the young were determined. Twenty-six such experiments were carried out.

Mothers in the control bottles, reared in approximately 10 ml. of medium per mother, produced an average of 12.3 young per mother, of which 27.9% were males.