Factors Involved in Male Production by Crowded Moina macrocopa Mothers.

Abstract

The writers, , have extended the earlier observations of Grosvenor and Smith and others on the association between crowding of Moina macrocopa mothers and the production of male offspring. We also noted an association between retardation in the time of production of the parthenogenetic young and the percentage of male young produced. Within limits the percentage of male young produced is roughly proportional both to the degree of crowding and to the amount of retardation in the time of their production. Excessive retardation, however, whether induced by crowding or by other treatments, is accompanied by a reduced percentage of male young. We have interpreted this retardation and this male production as due to the accumulation of the mothers' excretory products. Stuart and Banta have shown that quantity of bacteria available as food for Moina mothers appears, under certain appropriate experimental set-ups, to be the determining factor in sex control in this species. This finding might raise the question as to whether quantity of available food is the principal or sole influential factor involved in male causation in crowding or other experiments, by Moina mothers. In certain experiments involving aeration of mothers during the critical period male production was reduced or eliminated, in which case quantity of food apparently cannot be considered the determining factor in sex control. But the results of crowding might seem readily interpretable on this basis. This note records the results of experiments designed to differentiate between (1) the quantity of available food and (2) some other factor associated with crowding (presumably “the accumulation of excretory products”) as factors in influencing male production.