Kangaroo fathers modulate maternal control of offspring sex but not post-partum maternal expenditure

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.