Dominance Rank and Parental Investment in Swine (<i>Sus scrofa domesticus</i>)

Abstract

Abstract Using domestic swine, we tested the general prediction from life history theory that females increase their investment in offspring with increasing age and parity. Because increased investment may have a greater beneficial impact on the lifetime reproduction of sons than daughters, we also tested the prediction that older females would invest more in sons than in daughters compared to younger females. Finally, we examined whether age‐ or parity‐related patterns of change in reproductive effort were associated with differences in the social dominance ranks of females. Female swine from a large number of domestic breeds were assigned to social groups, and their dominance ranks were determined based on the outcome of agonistic encounters. The prediction that older females produce larger litters was supported, but the increase was related only to age, not to parity. Across all ages, high‐ranking females produced a greater proportion of sons than low‐ranking females. Contrary to our prediction, there was no rank‐related change in the proportion of sons born with increasing age or parity. However, the mean body masses offspring born to high‐ranking females increased with increasing maternal age and parity, but this was not the case for offspring of low‐ranking females. Studies of free‐ranging groups of swine are needed to determine whether an increase in body mass at birth would have different effects on the reproduction of sons or daughters.