EFFECTS OF MATERNAL FOOD DEPRIVATION ON REPRODUCTION OF OFFSPRING IN MUS MUSCULUS

Abstract

The Trivers and Willard (1973) model predicts that females of polygynous and promiscuous species have the ability to alter the secondary sex ratio of their offspring based on the particular ecological, social, or physiological conditions in which they are producing offspring, and that this adjustment of the sex ratio is adaptive. There have been many studies on the connection between maternal condition and sex ratio; however, there is little information concerning the effects of maternal condition upon the reproduction of the offspring. In this paper I report the results of an experiment which attempts to address this question, using Mus muscu/us as the test subjects. Two groups of Parental female mice were established. The Control group was fed ad libitum throughout gestation, while the Treated group was deprived of food every third day during the second half of gestation. The resulting Fl litters were used in the experiment, which was done in three parts. The first part examined the composition, sex ratio, and weight of the Fl pups. No significant differences were seen in these litters. The second part examined aspects of reproduction of the Fl females from the Control and Treated groups. Each group of Fl females was mated to Control males, and the resulting litters were examined for differences in sex ratio, pup weight, survivorship, and numbers of pups born. The Control Fl females gave birth to a higher proportion of male pups, and those male pups were heavier at weaning than the Treated pups. The daughters of Control Fl females were also heavier at weaning than their Treated counterparts. Additionally, the Control Fl females were heavier at parturition than the Treated Fl s, although there was no difference in weight at mating. In the third part of the experiment, male Fl pups from the Control and Treated group were matched for weight, and dominance trials were held to determine dominance/subordinance. The Control males were significantly more often the dominant male of the pair, and weight was not a factor in determining dominance. Several sex organs (preputial glands, seminal vesicles, and testes) were taken from the males used in the dominance trials, and the weight (wet and dry) of the organs was compared. Control Fl males had heavier seminal vesicles, weighed wet, and also had heavier wet preputial glands. These results, taken together with other evidence, provide support for several predictions of the Trivers and Willard model. This experiment supports the predictions that differential advantage in reproductive success is gained by adult males due to slight gains in condition; that the condition of the offspring tend to be correlated to the condition of the mother during the period of PI; and that Control Fl females have the potential for greater lifetime reproductive success than Treated Fl females. Additionally, the results of this experiment indicate that a modification of the model may be necessary to take into account the fact that food deprivation at less than the level needed for a sex ratio shift is still sufficient to cause changes in the offspring. This may mean that there is a limit to the female's ability to adjust the composition of the litter in utero.