Parents should bias sex allocation toward offspring of the sex most likely to provide higher fitness returns. Trivers and Willard proposed that for polygynous mammals, females should adjust sex-ratio at conception or bias allocation of resources toward the most profitable sex, according to their own body condition. However, the possibility that mammalian fathers may influence sex allocation has seldom been considered. Here, we show that the probability of having a son increased from 0.31 to 0.60 with sire reproductive success in wild bighorn sheep (Ovis canadensis). Furthermore, our results suggest that females fertilized by relatively unsuccessful sires allocated more energy during lactation to daughters than to sons, while the opposite occurred for females fertilized by successful sires. The pattern of sex-biased offspring production appears adaptive because paternal reproductive success reduced the fitness of daughters and increased the average annual weaning success of sons, independently of maternal allocation to the offspring. Our results illustrate that sex allocation can be driven by paternal phenotype, with profound influences on the strength of sexual selection and on conflicts of interest between parents.
Usage Notes:
Data from paternal reproductive success drives sex allocation in a wild mammal
The following variables are included on the file:
sex = lamb sex.
cohort = year of birth.
id.father = identity of father.
id.mother = identity of mother.
previous.RS = maternal reproductive success the previous year (a three-level factor: “failed” = 0, “weaned a female” = 2 , or “weaned a male” = 1).
TW1 = mother body mass in mid-September (about two months before conception) minus mean mass of this female at each reproductive event.
TW2 = mother mass minus the mean mass of the adult females that year.
neomortality = annual neonatal mortality.
paternalsuccess = log-transformed percentage of paternities assigned to each male in a given year.
ajusted.growth = residual summer mass gain of lambs.
data.xls