When sons and daughters have different fitness costs and benefits, selection may favor deviations from an even offspring sex ratio. Most theories on sex ratio manipulation focus on maternal strategies and sex-biased maternal allocation. Recent studies report paternal influences on both offspring sex ratio and post-partum sex-biased maternal allocation. We used long-term data on marked kangaroos to investigate if and how paternal mass and skeletal size, both determinants of male reproductive success, influenced (a) offspring sex in interaction with maternal mass, and (b) post-partum sex-biased maternal allocation. When mothers were light, the probability of having a son increased with paternal mass. Heavy mothers showed the opposite trend. A similar result emerged when considering paternal size instead of mass. Post-partum maternal sex-specific allocation was independent of paternal mass or size. Studies of offspring sex manipulation or maternal allocation would benefit from an explicit consideration of paternal traits, as paternal and maternal effects can modulated each other.

Data collection and processing is described in the paper.

Notes on data files and R scripts can be found in the file README.txt