Adaptive adjustment of the sex ratio: More data and considerations from a fallow deer population

Abstract

In polygynous mammals, it has been suggested that mothers in good condition with high ability to invest in their offspring would benefit (in terms of number of grand offspring) by producing sons, whereas mothers in bad condition would benefit by producing daughters. To test this prediction in the fallow deer, Dama dama, 211 births of 61 hinds with known reproductive histories, ages, and body masses were analyzed according to sex. The observed birth sex ratios of hinds who raised sons, daughters, or no offspring the previous year did not deviate significantly from unity or from each other. Two-year-old primiparous mothers who were not fully grown and presumably invested less resources in their offspring produced an equal number of sons and daughters. The sex ratio did not either deviate from unity for any other age class. Further, no estimates of maternal condition, such as body mass change during the summer before conception, body mass at conception, body mass change during the winter after conception, and body mass before birth, differed between mothers who gave birth to sons and those who gave birth to daughters. These results strongly suggest that adaptive adjustment of the sex ratio according to ability to invest does not occur in fallow deer.