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.

当子代雌雄个体具有不同的适合度成本与收益时，自然选择可能会倾向于偏离均等的子代性比（offspring sex ratio）。目前绝大多数关于性比调控（sex ratio manipulation）的理论均聚焦于母方策略与性别偏向的母方资源分配。近期已有研究表明，父方对子代性比以及产后性别偏向的母方资源分配均存在影响。本研究借助标记袋鼠的长期观测数据，探究了作为雄性繁殖成功率关键决定因素的父体体重与骨骼体型，是否以及如何通过与母体体重的交互作用，对（a）子代性别产生影响，以及（b）产后性别偏向的母方资源分配产生影响。当母体体重较轻时，产下雄性子代的概率随父体体重增加而升高；而体重较重的母体则呈现出相反的趋势。若以父体骨骼体型替代父体体重进行分析，可得到相似的结果。产后母方的性别特异性资源分配与父体体重或骨骼体型均无关联。针对子代性比调控或母方资源分配的研究，若能明确纳入父方性状的考量将更具价值，因为父方与母方的效应可以相互调控。